MATTNOYES.NET - Weather Website & Blog: December 2006

A BIT OF SATURDAY SNOW, SUN TO END 2006, AND A WINTRY MIX TO RING IN THE NEW YEAR

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

High pressure building south out of Quebec and across New England will lock in cold and relatively dry air heading into the weekend. With an upper level disturbance set to move across the area on Saturday, this will mean snow showers for a good portion of New England Saturday, with the return of reinforced cool and dry air for New Year's Eve day. By New Year's Day, a messy scenario will unfold across New England.

In the meantime, Friday morning clouds came courtesy of an upper level disturbance that brought moisture aloft to the region. In fact, radar scopes were lighting up with indications of rain and snow across Southern New England on Friday, but this was simply what we in the world of meteorology call "virga," or precipitation that falls from aloft, evaporating before it hits the ground thanks to dry air near the surface. The remainder of the day has brought a strengthening grasp of high pressure and dry air building south out of Canada, and this will mean increasing sun in the previously overcast areas, for a blend of sun and clouds regionwide. A brisk northwest wind will become northeast from north to south during the afternoon as the center of the fair weather cell moves directly overhead.

With this axis of fair weather, winds will be rather light and skies partly cloudy or mostly clear to begin Friday night. This will mean quickly cooling temperatures regionwide, ahead of an approaching upper level disturbance that will bring increased cloud cover late Friday night. It's an interesting battle that sets up for Saturday, as we'll have a somewhat conflicted weather map - high pressure and dry air at the surface, favoring fair weather, while the disturbance aloft will cause air to rise several thousand feet above our heads, favoring clouds and precipitation. One of the biggest questions in my mind is whether the precipitation may evaporate in the near-surface dry air upon descent, meaning some decent snow thousands of feet above our heads but not much going on here on the ground. While that's a concern of mine, it's not what the most likely scenario is - in fact, the reason I've kept precipitation in the forecast for Saturday over the course of the past several days is because this disturbance comes through while warmer and slightly more moist air is rebounding northward behind the eastward moving area of high pressure, on a developing southwest wind. The result should be for snow to make it down to the ground, and in fact, enough precipitation will result for some accumulation. Though amounts will be limited - especially south of the Massachusetts Turnpike where not much precipitation will fall and temperatures will be above 35 degrees - we should see an inch or so through a stripe of Central New England, with greater amounts where mountainous terrain will help to enhance the snow in Central and Southern Vermont. Timing appears to be from early morning to early afternoon west, and mid-morning to mid-afternoon Central and East. Though not much snow will fall, temperatures near freezing may mean some roads become slick and snowcovered, requiring some light treatment.

SATURDAY NOTE: Higher amounts drawn on this map for the Central and Southern Green Mountains appear as though they will also verify farther North up the spine of the Greens and into the higher terrain of New Hampshire, with the 1" line extending all the way into the Mountains of Maine and perhaps even the Portland area! You can follow the snow through radar links at right.

Behind Saturday's disturbance will come a reinforcing shot of cold air for Sunday. Of course, as has been the case, this cold Canadian air is also dry air and that should mean the return of sunshine, though wind chill will once again be a factor with an active breeze. Nonetheless, this new dome of fair weather will hold at bay advancing moisture ahead of the major Rocky Mountain storm. Of course, this storm has been raking Denver (see Weather News Headlines in the top right corner of this page) with a couple of waves of heavy snow, wind and near-blizzard conditions that will continue through Friday night. This strong Rockies storm sweeping northeast across the nation's midsection will pivot north, while the energy aloft that drove its development shifts east, resulting in a new wave of low pressure developing in the Tennessee River Valley over the course of the weekend. This new storm will tap the Gulf of Mexico as it winds up Saturday, but the northeast surge of this moisture will be slowed significantly by our freshly reinforced cool and dry airmass, associated with the center of new Canadian high pressure sliding across New England.

Gradually, this dry air will lose a bit of its grip on New England as the ridge of high pressure slowly moves east of New England. Though this will allow a bit of a milder southeast flow for some of New England, what it will also do is break down our protection to allow moisture to stream in, moving from southwest to northeast. At this point, the trend in meteorological guidance continues to be to slow this system significantly, with most forecast tools now not forecasting arrival until after midnight Sunday night! Though, as mentioned yesterday, I'm still quite hesitant to trust Gulf moisture as it almost always arrives ahead of schedule, this trend does seem to bode wonderfully for the many First Night and outdoor events across New England, and I'll put aside my distrust of the pattern given overwhelming agreement among guidance on a dry New Year's Eve through midnight.

By New Year's Day, however, the approaching moisture will have successfully battled its way through the retreating dry airmass and will result in developing precipitation across New England from southwest to northeast. With cold air just beginning to let go, the potential exists for many areas to begin with a burst of wintry precipitation, though as high pressure slides southeast of New England and winds turn to blow from the south and southeast, most of Southern New England is likely to transition to raindrops. The farther north one is on New Year's Day, however, the better the chance of snow, as a small bubble of cold Canadian air will be situated over Quebec, and will help to hold the cold in place across Northern New England as moisture moves in. The result should be another accumulating snow event for the mountains - fantastic news for ski and snowmobile country - while a rain/snow line is likely to set up somewhere around Central and Southern Vermont/New Hampshire/Maine. Though it's early to pinpoint the location of this line, the pattern would favor it falling somewhere near the Lakes Region of New Hampshire, and inland several miles from the coastal plain of Maine.

By Tuesday, this storm will move north of New Enlgand and sit for awhile. This will effectively block any deep cold from moving south out of Quebec for a few days, and rather mild temperatures may be the result for the middle of the week.

Technical Discussion: Out by early afternoon.

Matt

Matt's Technical Meteorological Discussion: Updated Friday, December 29 at 12:40 PM

Rest of today is self-explanatory, tonight is fairly straight-forward. Sat brings challenges with precip placement and amount. The NAM was too far north at 00Z in my estimation, and started to come more in line in the 12Z run. GFS probably was too far south at 00Z and looks pretty good in 12Z run. Vort max will, of course, be the driving force for dynamically forced lift that will initiate precip Sat AM. The track of the center of this vort is from the NW shore of Lake Ontario to the coast of Ern MA, and it is a channelled vort, meaning the area of PVA is rather narrow. Synoptic reasoning tells us precip will occur in areas of PVA/CVA, but also that heaviest precip should occur in region of warm advection, which will occur just north of the path of the vort. Therefore, this supports heaviest band of precip in Srn VT/NH and perhaps Nrn MA, and this is the course I've followed. Of course, that reasoning alone wouldn't have been enough - also have taken baroclinic zone into account, which is pronounced at 850 mb. This baroclinic zone was present over esp Srn NewEng Fri AM with a band of clouds and virga, and the heaviest clouds/virga were found near the -5 850 C isotherm. How ironic (not) that the -5 C 850 mb isotherm has long been the historical guide for heaviest snow thanks to aggregating flakes. This occurrence of no precip at the sfc but great signatures on satellite and radar was like a free gift with regard to clues from the atmosphere! I'd expect heaviest precip to fall near this -5 C isotherm on Sat, which drops south during the day as the atmosphere saturates. There is the challenge of contending with a 1036 high centered right over NewEng and still trying to squeeze out precip, as model RH cross sections show a dry layer below 900 mb and that is concerning for evaporation, but with warm advection occurring right down to the sfc as winds swing from the SW and blow across isotherms and thickness contours at many levels in the lower and middle several thousand feet of atmosphere, I have to assume we will saturate. QPF amounts are in fairly good agreement, so nailing the axis is key here, though ratios will play a role. Lift near 600 mb will be in favorable dendritic crystal growth but boundary layer temps will be close to freezing and some areas of Srn NewEng will be above freezing, with areas south of the MA Turnpike likely to exceed or meet 35 degrees, at which point accumulations are short-lived or not at all. Therefore, will have to be north of the Pike and ideally in heart of lift and forcing to see accums, and that's what's been indicated in the map above, in the General Wx Summary. Went cooler than statistic guidance for max temps thanks to cold start and dry air allowing for evaporational cooling with precip thru most of day.

Certainly have to buy into the late trend for New Year's Eve even tho I don't trust Gulf Moisture - the new Canadian high provides some level of comfort in keeping moisture at bay. As the high shifts east of NewEng, however, winds will turn from the SE and of course we know that's a warm ocean direction that will scour out cold air quickly across Srn NewEng. If the precip comes in fast enuf, at least a mix is possible early in the game, but that would be extremely short lived and probably limited to the hilly terrain of the interior in Southern NewEng. The cold air in place Sun and Sun Ngt is dense enough, however, that it should hold on across the North Country where I'd expect an accumulating snow New Year's Day. Logic would seem to say that a very similar pattern to last week, with a slightly stronger high, slightly farther into the cold season, should suggest a rain/snow line a bit farther south than the last time around - perhaps into Central VT/NH/Central or Srn ME - though in these marginally cold areas an elevation dependence would likely exist.

Once that storm moves north, it sits along with the primary low to our west for awhile and this will effectively cut off the route for cold air to make its way southward from Quebec, which is truly the only area nearby with appreciable cold on the east side of the low level Central Canadian ridge. The result will be for a rather mild stretch, I would suggest, for the middle of next week in what will be "occluded air" - air behind the occluded front which is of Southern origin after the passing of the Gulf infused storm.

In the longer range, it's discouraging for winter lovers to see Ensemble mean forecasts of thicknesses during the middle of January to be the same as they are today. In fact, over the course of the next two weeks, the deviation of average column temp is rather small, indicating to me that NewEng will remain in marginally cold airmasses for quite some time to come. Remember what was discussed here previously - that with cold built up in Eastern Canada it will at least be available when storms do develop. So when can we get a storm in here?! Another storm will crank up the coastline Friday into Saturday at the end of next week, but once again it will be difficult to hold cold air in at least Southern areas without a strong high over SE Canada. There is at least some hope, however, in the fact that a frontal boundary will lay draped near the East Coast through the middle of the month, and as a west coast trough deepens a bit by that time period, energy will eject east and moisture will be available along this front. Therefore, New England remains in a milder than normal pattern, but at least one with potential when storms develop, for the next couple of weeks, while colder than normal air finally makes it onto the map by the end of the period, found in the Western US trough.

Happy New Year - thanks for making 2006 a great one by visiting all through the year!

Matt

Wednesday's Discussion:

1:55 PM: Clouds continue to blossom with passage of shortwave trof and weak windex event as lingering low level moisture and instability are focused with combo of sluggish sfc cold front and well defined upper level shortwave. The available upper level diffluence has been sufficient to prompt snow and rain showers where frontal forcing and orographic forcing intersect, tho lots of virga in those radar returns owing to moderate dewpoint depression in sfc obs. Expect activity to wane south as available moisture decreases tho Nrn Mountains may find new snow showers developing afternoon and eve with vort max passage as evidenced on water vapor imagery.

Not bone-chilling cold Wed ngt but Tds in the teens and 20s will support similar overnight lows as winds gradually subside and clouds gradually diminish with loss of low level instability as diurnal effects wane. Another disturbance slated for Thu afternoon aloft will focus snow showers near frontal boundary, which is fcstd to waver N and therefore best focus for snow showers and perhaps a few squalls will be Nrn NewEng and esp where upslope flow is favored. Elsewhere, mixing will result in another breezy day with temps near Wed levels.

Sat there was little support of precip in 00Z guidance but noticing 12Z guidance coming around which makes sense and fits the forecast I have going, so hopefully the trend continues. Just makes sense to crank out at least light precip (rain/snow likely mostly snow with cool low levels) given steady weak warm and moist advection and weak vort aloft. Main precip from Central US storm will still be SW of area until late Sat Ngt or perhaps even Sun. The trick here is how quickly the ridge crests over NewEng and the trend on that has been slower, but last time we saw the operational guidance trend slow while the Ensembles stayed on course and the Ensemble guidance from both GFS and Canadian say bring the rain in late Sat night/Sun as ridge axis passes, so will hold steady on that for now. As for ptype, logic would dictate that in a similar longwave pattern, if a high of equal or greater strength (this one greater than last) settles to similar position (this time a bit farther south over Southern NewEng) later into the cold season, expect cold to penetrate a bit farther. Tho guidance is a bit spread on baroclinicity, the mean seems to agree with this line of thinking and this shud mean another mountain snow with a rain/accumulating snow line a bit farther south than the last time around for Sun. Thereafter, the first half of next week will bring occluded air, not a shot of cold, and in fact air behind an occluded front often can be mild as the cyclone blocks the southward progression of cold.

The question is, would there be any cold available anyway? The GFS Ensemble mean 850 temp anomaly shows some +16-+18 C anomaly over Central Canada, and while that would typically lead one to believe there's no available cold, keep in mind that warmer average temp in a column is associated with a ridge, and a sfc/llvl ridge centered over Central Canada keeps a shallow flow of cold air from the North Pole to Eastern Canada. This is reflected in guidance progs of -20 C and colder at 850 over Eastern Canada, and in fact, this low level cold is partly what helps out the North Country with this upcoming weekend storm, because while the flow goes SE, any ageostrophic flow would bleed intense shallow cold southward. Farther out, though we're blocked from the cold by the mature cyclone spinning over the Northeast and Southern Canada, the persistent sfc ridge over Central Canada continues to load cold into Eastern Canada and this will mean a steady drain of cold air that will be readily available when the right synoptic situation comes along.

Enjoy your day.

Matt

VARYING CLOUDS BUT NO MAJOR NEW ENGLAND STORMS FOR NEXT FEW DAYS...

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

A slow moving front will sag across New England on Wednesday, and will waver across the six-state region through the end of the week, bringing varying amounts of cloud cover and ensuring no quick transitions to deep Canadian cold, nor to milder air south of the region. Overall, this leaves most of us in a "no man's land," so to speak, though occasionally strong storms can develop along frontal boundaries if a strong enough disturbance encounters the airmass clash. With no strong disturbances in sight for New England, however, we will instead see an extended period of clouds, sun, and light showers of rain and snow.

That pattern takes hold today, with morning rain and snow showers exiting Eastern areas early with the passage of an upper level disturbance, and another disturbance moving east out of New York State, depositing continued showers of snow on Western New England. Elsewhere, a northwest wind will slope down off the mountains and hills of New England - resulting in a "downsloping" wind for most of New England, which serves to dry the atmosphere. This will help to squash most snow showers that try to escape east across New England, and will help to break up cloud cover and bring some sunshine out for most locales. Last to see emerging sun will be Cape Cod, while Northern and Western mountains will see at least scattered snow showers by later Wednesday afternoon.

Most mountain snow showers will end Wednesday night as drier air moves into New England from Southern Canada, and many communities will find partly cloudy and cool conditions during the overnight. With the aforementioned front lingering over New England on Thursday, expect similarly breezy and cool conditions to prevail, and a late-day disturbance aloft should develop a wave of low pressure at ground level, serving as the focus for Northern New England and especially mountain snow showers Thursday afternoon and evening, while Southern areas are likely to remain dry. While this pattern certainly isn't as helpful as a series of snowstorms for ski areas, the bright side about all of this is that it brings a fantastic pattern for making snow, with most nighttime AND daytime temperatures cold enough in the Northern Mountains. Farther south in New England, ski areas will rely on overnight snow production to boost conditions, but cold nights should ensure that conditions continue to improve where snowmaking takes place.

By late in the week, this cool fair weather cell will merge with another, larger bubble of high pressure moving over the Mid-Atlantic coastline, and this will mean a possible slight moderation in temperatures for Friday, though a cool northwest wind flow is still likely to persist and therefore little noticeable change is likely to evolve. By next weekend, another energetic upper level disturbance will be ejecting east after churning across the Rockies and Plains, resulting in another swath of moisture pluming out of the Gulf of Mexico and thereby bringing another likelihood of rain - perhaps mountain snow if cool air can hold on long enough and especially in the mountains of the North - though not until after what is likely to be a dry day Saturday as a slow-moving ridge of high pressure begrudgingly lets go of the Northeast.

Though the overall pattern will feature above normal temperatures for most of Canada for the next couple of weeks, and there is no screaming signature of a major snowstorm for the Northeastern U.S., it's important to understand that while no deep cold can penetrate a pattern like this over the average for the time period, high pressure over Central Canada can allow surface and low-level cold air to sneak southward into Eastern Canada, making it available to New England when the right storm comes along. Therefore, while I certainly can make no case for deep arctic chill, each storm will bring great interest in the coming weeks.

Matt

Matt's Technical Meteorological Discussion: Updated Wednesday, December 27 at 1:55 PM

Clouds continue to blossom with passage of shortwave trof and weak windex event as lingering low level moisture and instability are focused with combo of sluggish sfc cold front and well defined upper level shortwave. The available upper level diffluence has been sufficient to prompt snow and rain showers where frontal forcing and orographic forcing intersect, tho lots of virga in those radar returns owing to moderate dewpoint depression in sfc obs. Expect activity to wane south as available moisture decreases tho Nrn Mountains may find new snow showers developing afternoon and eve with vort max passage as evidenced on water vapor imagery.

Not bone-chilling cold Wed ngt but Tds in the teens and 20s will support similar overnight lows as winds gradually subside and clouds gradually diminish with loss of low level instability as diurnal effects wane. Another disturbance slated for Thu afternoon aloft will focus snow showers near frontal boundary, which is fcstd to waver N and therefore best focus for snow showers and perhaps a few squalls will be Nrn NewEng and esp where upslope flow is favored. Elsewhere, mixing will result in another breezy day with temps near Wed levels.

Sat there was little support of precip in 00Z guidance but noticing 12Z guidance coming around which makes sense and fits the forecast I have going, so hopefully the trend continues. Just makes sense to crank out at least light precip (rain/snow likely mostly snow with cool low levels) given steady weak warm and moist advection and weak vort aloft. Main precip from Central US storm will still be SW of area until late Sat Ngt or perhaps even Sun. The trick here is how quickly the ridge crests over NewEng and the trend on that has been slower, but last time we saw the operational guidance trend slow while the Ensembles stayed on course and the Ensemble guidance from both GFS and Canadian say bring the rain in late Sat night/Sun as ridge axis passes, so will hold steady on that for now. As for ptype, logic would dictate that in a similar longwave pattern, if a high of equal or greater strength (this one greater than last) settles to similar position (this time a bit farther south over Southern NewEng) later into the cold season, expect cold to penetrate a bit farther. Tho guidance is a bit spread on baroclinicity, the mean seems to agree with this line of thinking and this shud mean another mountain snow with a rain/accumulating snow line a bit farther south than the last time around for Sun. Thereafter, the first half of next week will bring occluded air, not a shot of cold, and in fact air behind an occluded front often can be mild as the cyclone blocks the southward progression of cold.

The question is, would there be any cold available anyway? The GFS Ensemble mean 850 temp anomaly shows some +16-+18 C anomaly over Central Canada, and while that would typically lead one to believe there's no available cold, keep in mind that warmer average temp in a column is associated with a ridge, and a sfc/llvl ridge centered over Central Canada keeps a shallow flow of cold air from the North Pole to Eastern Canada. This is reflected in guidance progs of -20 C and colder at 850 over Eastern Canada, and in fact, this low level cold is partly what helps out the North Country with this upcoming weekend storm, because while the flow goes SE, any ageostrophic flow would bleed intense shallow cold southward. Farther out, though we're blocked from the cold by the mature cyclone spinning over the Northeast and Southern Canada, the persistent sfc ridge over Central Canada continues to load cold into Eastern Canada and this will mean a steady drain of cold air that will be readily available when the right synoptic situation comes along.

Enjoy your day.

Matt

THICK FOG FAR SOUTH, SNOW FAR NORTH, GRAY AND RATHER DULL IN BETWEEN

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

A progressive storm will march across Southern New England at the surface on Tuesday, though the upper level energy driving this storm development will swing from Upstate New York to the Northern border of New England through the day. With the deep feed of tropical moisture already east of New England, little significant precipitation will fall aside from drizzle in Southern and Central New England, though the upper level disturbance will spawn new areas of rain and snow in Northern New England later Tuesday.

Rain fell heavily at times Christmas night across Southern New England, briefly mixing with snow for some areas at the onset, while Northern New England remained just barely on the cool side of a marginally cold airmass to support snowfall. This meant a heavy, wet snow across the North, with a few inches in most higher terrain locales but a very sloppy slush for many areas. Dick Sharron, one of our weather observers in Glen, NH, reported 2" of snow, but nearly half an inch of liquid equivalent in that snow - that's sloppy stuff! With temperatures hovering near or just above freezing for most of the North Country Tuesday afternoon, the approaching upper level disturbance that will serve as the second half of this storm will bring a mix of rain and snow, heavy at times, but the continued wet and sloppy nature of the snow will mean less accumulation than one would normally anticipate - probably only a few additional inches in the higher terrain. Additionally, the marginal temperatures will mean most road treatments work well today, though heavier bursts of snow may cover up roadways from time to time with a greasy slush.

Farther south, through the remainder of New England, temperatures will be heavily dependent upon where one is in relation to a wave of low pressure rippling across Southeastern New England - to the south of the track, places like Cape Cod and the South Coast have seen very mild air resulting in very thick fog. North of the storm path, a cool northeast flow will maintain areas of drizzle, some fog, and cool temperatures. Drizzle and a few light showers are all that's expected, however, thanks to very dry air moving overhead several thousand feet in elevation. This dry air will make most of the clouds over Southern and Central New England too shallow to produce widespread significant precipitation.

By Tuesday night, colder winds will blow from the northwest, and this will result in "upslope flow", where air flows up the Western slopes of the Green and White Mountains, forcing the air upward, resulting in clouds and precipitation, which is why I'd expect snow to linger along these mountain slopes through Tuesday night, with some additional accumulation as the sun sets and temperatures cool, allowing a few inches to accumulate in higher terrain of Northern New England Tuesday evening into Tuesday night. Elsewhere, a few flurries are possible with the onset of colder air, though for the most part a drying trend will begin Tuesday night and continue into Wednesday and Thursday - two chilly and breezy days with a blend of sun and clouds ahead of the center of another cool Canadian high pressure center.

By late in the week, this cool fair weather cell will merge with another, larger bubble of high pressure moving over the Mid-Atlantic coastline, and this will mean a possible slight moderation in temperatures for Friday, though a cool northwest wind flow is still likely to persist. By next weekend, another energetic upper level disturbance will be ejecting east after churning across the Rockies and Plains, resulting in another swath of moisture pluming out of the Gulf of Mexico and thereby bringing another likelihood of rain - perhaps mountain snow if cool air can hold on long enough and especially in the mountains of the North - though not until after what is likely to be a dry day Saturday as a slow-moving ridge of high pressure begrudgingly lets go of the Northeast.

Technical Discussion: None today.

Matt

NO SNOW TO GREET US CHRISTMAS DAY...BUT CHRISTMAS NIGHT SHOWS SNOW ON THE WAY! FOR SOME.

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

Merry Christmas! The center of a fair weather cell - an area of high pressure - is moving southeast across the Northeastern United States on this Christmas Day, and that's helping to hold cool and dry air in place across New England for the time-being. Nonetheless, the air in place is only marginally cold - that is, borderline for rain or snow across the six-state region - and that will become very important as moisture streams northward from the Gulf of Mexico. By the time all is said and done, this next slug of moisture and the associated strengthening storm moving across New England will deliver a dumping of snow to the Northern Mountains, and mostly rain farther south.

The first signs of increasing moisture have already become evident as high-altitude clouds across an earlier sunny Christmas morning sky. These clouds will gradually thicken throughout the day, and showers will develop across Southern New England around dinnertime. In fact, late-arriving dinner guests may come with umbrellas! You can follow all precipitation through the radar links at right over the course of the evening. For many of us, daytime temperatures in the 40s and 50s will leave an atmosphere too warm in the lower few thousand feet to support any snowflakes, and raindrops will be the result. The air, however, is dry, and where saturated the temperature will fall so that some higher terrain will cool sufficiently for rain to change to snow. This phenomenon should take place from the Berkshires to the Worcester Hills between 10 PM and midnight before changing back to rain as warm air is swept in on a southerly wind, while areas farther north will see a longer-lived period of snow. For many areas of Central and Southern New Hampshire, Vermont and Maine, any snow that falls will be rather wet and sloppy, leaving some slush in communities like Concord, NH, and perhaps Portland, ME, for the Tuesday morning commute, where snow should have changed to rain by that point but melting of the coating to an inch that will have fallen will still be underway. Farther north still, our marginal airmass should be just barely on the cold side of that margin, meaning that most of what falls in the Northern Mountains will be snow.

In the North Country, equally important to determining snowflakes are likely to fall is the ratio of snow to water - that is, I'm expecting some of Northern New England to receive .75" of liquid equivalent precipitation Monday night through Tuesday night, but the temperature of the atmosphere aloft is what's critical in determining the type of snowflake that will fall. With temperatures just barely below freezing in the lower several thousand feet of the atmosphere, conditions will be favorable for large aggregates - that is, huge flakes that are wet in nature and will compact quickly, limiting how quickly they can accumulate. The higher one is in elevation, the less sky snowflakes will have to travel through at near-freezing temperatures, and therefore the lighter and fluffier the snow will be. This should result in a large difference in accumulation between valley and mountaintop, with higher amounts in higher elevations.

In Southern New England, Tuesday morning showers will linger through the day - but truly only as showers and drizzle and unlikely to be a steadier rain thanks to very dry air moving overhead several thousand feet in elevation. This dry air will make most of the clouds over Southern and Central New England too shallow to produce widespread significant precipitation. Farther north, more moisture will be available deeper in the atmosphere, and a new swath of upper level energy will swing through during the afternoon - two good reasons to expect periods of steadier and heavier precipitation to continue.

By Tuesday night, colder winds will blow from the northwest, and this will result in "upslope flow", where air flows up the Western slopes of the Green and White Mountains, forcing the air upward, resulting in clouds and precipitation, which is why I'd expect snow to linger along these mountain slopes through Tuesday night, with some additional accumulation. Elsewhere, a few flurries are possible with the onslaught of colder air, though for the most part a drying trend will begin Tuesday night and continue into Wednesday and Thursday - two chilly and breezy days with a blend of sun and clouds ahead of the center of another cool Canadian high pressure center.

By late in the week, this cool fair weather cell will merge with another, larger bubble of high pressure moving over the Mid-Atlantic coastline, and this will mean a moderation in temperatures for Friday. By next weekend, another energetic upper level disturbance will be ejecting east after churning across the Rockies and Plains, resulting in another swath of moisture pluming out of the Gulf of Mexico and thereby bringing another likelihood of rain - perhaps mountain snow if cool air can hold on long enough.

Technical Discussion: None today...have a wonderful Christmas!

Matt

"HO, HO, HO! NOW WHERE'S ALL MY SNOW?"

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

The cold start across New England Friday morning is indicative of a Canadian high pressure cell centered over the region. Though the air early Friday is plenty cold enough for snow, the increasingly progressive pattern of the atmosphere will mean warm air can quickly invade New England and most of what falls Friday night and Saturday will come down as raindrops. Meanwhile, Denver warms above freezing today but digging out is still first priority, and London, England, continues to see thick fog and areas of freezing fog, hampering travel there, as well.

Relatively speaking, that means New England is quite fortunate! Nonetheless, the pressure is on nature to deliver snow in time for Christmas, and it appears as though she will buckle under the pressure - at least if you're hoping for snow by Christmas morning. In the meantime, with a surface fair weather cell cresting over New England Friday, winds will be light and variable and this certainly won't help any warm air to move into New England. In fact, as moisture spills in aloft, thickening clouds will have many folks looking to one another saying, "It sure feels like it could snow!" While the sky may have a snow look and the air a snow feel, however, a cold rain will be the fate for most of New England. Our first clue to this comes from observations across New York State, where only brief bursts of snowflakes quickly went to rain, and those areas that were below freezing still saw a change to freezing rain. The reason for this is a surge of warmth aloft - a trait common in surges of Gulf of Mexico air that flows nearly unabated up the Eastern Seaboard. Radar imagery is impressive across the Southeastern U.S., representative of the deep tropical moisture streaming northward.

Friday's thickening clouds will eventually push rain showers east from New York and into New England. You'll be able to monitor these showers Friday evening as they enter New England through the radar links at right, and the surge of moisture will allow rain to continue blossoming east through the overnight Friday night. Most areas, as mentioned, will be mild enough for rain thanks largely to daytime temperatures warming well above freezing before the blanket of clouds moved in and trapped that warmth. A smaller factor will be winds blowing milder air in - small only because of the light nature of the wind through Friday. These winds will increase Friday evening and Friday night, however, and will continue to bump both the temperature and the dewpoint - the measure of the amount of moisture in the air - upward across New England. In a few deeper valleys - especially valleys between mountains from the Berkshires to the Greens to the Northern Whites, and frankly, through a large chunk of interior Maine, air will still be dry enough that as rain falls into it, some of the raindrops will evaporate. Just like we feel chilly when we step out of the shower and water evaporates off our skin, evaporation is a cooling process and the air will cool as a result of these evaporating raindrops. The result will be some pockets of sub-freezing temperatures in the areas mentioned, and these pockets will find a period of freezing rain Friday evening into Friday night, creating slick spots. As breezes increase Friday night - blowing out of the southeast but increasing in velocity on a path from southwest to northeast across New England - each of these pockets of cold air will gradually be eroded, leaving plain rain for Saturday.

Periods of rain will fall heavily at times on Saturday, especially in the morning across Central and Southern New England, then just after noon across the North. Temperatures will respond to fresh southerly breeze in Southern New England and will rise into the 40s, though Northern New England will see continued cold rain as temperatures hover in the 30s. Total rainfall amounts will come to 2" for some along a stripe from CT to Central/Wrn MA and into the White Mountains, while most of New England will record between one and two inches of rain. This is unlikely to cause any problems with flooding, though the moist atmosphere will leave plenty of fog around Saturday night. Therefore, even as rain wraps up by suppertime Saturday in most of Central and Southern New England, fog may slow your holiday travels.

With no substantial slug of cold air to stream in behind the departing storm, Sunday will be a rather mild day - especially in Southern New England where a few spots may cross 50 degrees! Farther north, closer to cool Canadian air, temperatures will be noticeably cooler than your southern counterparts, but still quite pleasant for outdoor winter sports. By late Sunday afternoon into Sunday evening, an upper level disturbance zipping east along the Canadian border will move over Northern New England, bringing a few rain and snow showers Sunday evening and night, and tugging cold air southward out of Canada for Christmas Day.

Meanwhile, over the South Central United States, a strong, energetic disturbance will be marching eastward. This disturbance will be traveling through a trough (a dip) in the jet stream winds aloft. Remember that the jet stream is the fast-moving river of air that steers our storms and acts as a thermostat for the atmosphere, and will be flowing from the trough over the South Central U.S., to a position just south of New England. This means we'll be on the cool side of the jet stream, and it also means any storms to travel near to the jet stream will be steered toward Southern New England. Expect this new southern storm to be no exception to that rule, ready to truck northeast on Christmas Day.

Still, a storm over Arkansas Christmas Eve would have a very long way to travel in order to get here by Christmas Day, and that's a highly unlikely trip for it to make by Christmas morning. Therefore, expect your Christmas to begin dry and likely with sunshine, although temperatures will be quite chilly in the early morning, ensuring that while the day may not start out looking like Christmas, early risers will at least have the feel of Jack Frost nipping at your noses. Clouds will increase during the day on Christmas, and we're likely to be left with a very similar day to what Friday has revealed - temperatures climbing into the 40s and sunshine fading behind thickening clouds. Though the feel here at the ground will be similar, thousands of feet above our heads there air will be cooler, and that will be the key to precipitation type. In fact, the key to the Christmas night forecast is how long the cold air can hold on across New England, as the incoming storm being steered by the jet stream winds aloft will follow the path where cold and warm air are at odds. It appears as though that path would be laid out across New England, meaning the storm center could pass directly overhead. If that were to be the case, developing precipitation later Christmas Day would start as rain in Southern New England (remember, temperatures will be in the 40s), then - if everything played out just right - could flip to snow for a brief time Christmas evening before changing back to rain as warm air overwhelms any cooling processes inside the storm. Admitedly, at four days out this is a rather fancy detail to try and pinpoint, so for now I'd suggest it's only a possibility of how a brief period of snow could fall on Christmas evening before washing away. Farther north, enough cold air will be in place that this could be the mountain snow we've been waiting for, though exact storm path will depend on the location of the aforementioned airmass clash, and slight jogs south or north will have an impact on the rain/snow line, which at this point looks like it would march as far north as Central or Northern New England by Tuesday morning.

During the day Tuesday, if the storm were to cross Southern New England, drier air would move overhead thousands of feet aloft, tapering precipitation in Southern New England and along the storm path for a time before wraparound snow would settle southward behind the storm into Northern...then eventuallly Central New England later Tuesday. Regardless of how this storm plays out, the pattern will remain quite active with a series of strong Pacific disturbances traversing the country for the next couple of weeks. This certainly raises the potential for a number of moist storms to affect the country, and with a persistent trough in the jet stream over the Eastern half of the U.S., the Eastern Seaboard would remain in the line of sight. That said, there are also no signs of any deep intrusion of cold air to the Northeast, which means each one of these moist events may walk the line between rain and snow until the end of the month. Thereafter, a few factors will combine to keep hopes of winter from completely fading - one will be the stronger establishment of an Eastern U.S. jet stream trough, which would allow near-normal air to spill southward for the start of the New Year, and a much stronger presence of deep cold from Alaska to Northern Canada, indicating the well of cold air will finally be refilling for the Western Hemisphere, which is something we've lacked of late.

Technical Discussion: None today. Enjoy the weekend and MERRY CHRISTMAS!

Matt

Matt's Technical Meteorological Discussion: Updated Thursday, December 21 at 2:35 PM

Short term remains rather straight-forward tho winds will stay active overnight esp in Nrn NewEng, and this upslope flow combined with cold advection will bring increase llvl instability. Already have seen resulting cloud production along Canadian border this afternoon and expect this trend to continue southward with midlvl cooling, and this will result in mountain flurries and snow showers. Farther south, few clouds will blow thru but that should be about it.

Good agreement on dry Fri with increasing high altitude moisture after NW flow relaxes. Also good agreement on bringing precip in Fri night to most areas and after a trend toward significant slowing, speed has once again increased in the guidance so SW NewEng encompassed by Fri eve and just about all of NewEng encompassed overnight. This quicker onslaught of moisture in the guidance is part of the overall unpredictability of the pattern that's been discussed here the past couple of days with fast jet stream flow, tons of vorticity maximums and plenty of moisture available. The incoming moisture comes with increasing warmth in this case, and likelihood of evaporative cooling enuf for any frozen precip in the far Nrn mountains as mentioned yesterday has decreased to almost nil. Therefore, this will be a rain event for one and all. And it will be a heavy rain event! Good Gulf connection teams with strong PVA to really crank precip and good agreement among nearly all guidance of around 2" precip in rather large band of heaviest precip that will set up along path of 850 mb low center, where warm advection and isentropic lift is maximized, and this should be across CT, Cntrl/Wrn MA, Cntrl/Srn NH. Just about all areas can handle this rainfall without a problem - closest call is SCentral coast of CT where 6 and 12 hr flash flood guidance is around 2.5-2.75". No vegetative uptake will mean lots of runoff, but relatively dry antecedent conditions and no snow will mitigate. Shot of rain synoptically should come with warm advection, so Srn NewEng sees rain taper later Sat and Sat evening events - save for some dense fog - may be OK in Srn NewEng, esp the farther SW one is.

Of course, all eyes are on the latter period which I've described the past two days in as much detail as possible, though we've been waiting for confirmation of some of the details laid out here yesterday. Most of those details - especially the ones laid out here in the technical disc where you got a bit more of my inside thinking than in the General disc - seem to be coming together in the guidance so far (please reference previous disc below if you need a refresher). That is, the Sunday shortwave brings in marginal cold, the jet stream shifts S of New Eng Mon, and the next upper low needs to find a way from the Srn Plains to the East Coast of the US. It can find that way but it'll be tough to get it there by midday Christmas...still, one possibility discussed here yesterday still is on the table, which is to eject a piece of vorticity northeast into the confluent flow and develop a rather flat front-running wave that could deliver some precip to esp Srn NewEng on Christmas Day, but at that point the air may be just on the warm side of marginal and even if that happens it may come down as raindrops. Still, I see this as a low probability scenario, with the more likely scenario to wait until the more substantial energy shoots east, by which point a bubble high of llvl cold over SE Canada has been able to muscle cold air S, and this, aided by evaporational cooling, would help to make ptype snow in many areas Mon Ngt into Tue. With such a marginal airmass, and the precip type relying upon a relatively weak bubble high north of NewEng, there is likely to be a rain/snow line which - between the marginal airmass and still relatively warm ocean - may penetrate pretty far inland and north, even perhaps up to Central/Srn NH. But this is a detail that shouldn't be worked out now...there is still a great deal that can change between now and 12/25-26, so for now we'll stay focused on the pattern and getting this storm to form, then we can worry about the rest.

Go get your shopping done!

Matt

Wednesday's Discussion:

1:15 PM: A brief discussion today to address some key points to the coming forecast.

Quiet in the short term with temps tonight warmer than last thanks to increasing SW gradient flow and at least a few clouds that will traverse NewEng assoc with frontal boundary settling S across NewEng in response to shortwave traversing Ontario and Quebec. This boundary should sit over Srn NewEng most of Thu and midlvl thermal and theta-e gradient along with slight directional wind shift will be the impetus for cloud development in Central and Srn NewEng, shifting S thru the day as midlvl front sags southward. This will be a similar tho milder scenario to what is playing out over MN today with this shortwave. Dry low levels should preclude most precip, though a few flurries can't be entirely ruled out in Srn NewEng morning to midday.

Cool and dry air holds strong on Fri with NW flow leading into confluent flow E of NewEng as warm and moist advection works NE. Trend continues to be going slow on precip advancement for weekend storm, appearing more likely as a late Fri night into Sat start time. Tho 850 temps may go to near zero in NH and ME mountains, air still will be rather dry and wet bulb temp will be subzero so as precip moves in and atmosphere saturates we should see at least a period of snow in the Nrn NH/ME mountains, though warm advection wins the battle for most. From the mountains of Maine to Nrn ME, we may hold the cold just enough for a change from snow to sleet or freezing rain rather than rain. With triple point development likely, precip should be locally heavy in Central/Srn NewEng for part of Sat.

Farther out, my thinking from yesterday hasn't changed much, so for those of you who didn't have a chance to read I'll first direct you to the discussion below this one. What I do see happening is what I've tried to explain in layman's terms in the General Weather Summary above, which is this: Current upper low moves thru Great Lakes and merges with upper low over James Bay. This pivots Wrn Canada strong shortwave under the belly of these merged lows, ejecting in quickly E along the Canadian border and into NewEng later Sun. It will encounter air that won't be all that cold given the occlusion from Sat and the lack of any cold behind the storm to sweep in, so showers along the greatest PVA of Nrn NewEng still may be a mix of rain and snow latter half of Sun, but will end as snow showers with colder air streaming in behind the shortwave. Tho I still see the possibility of a piece of Srn energy ejecting sooner than anticipated and therefore passing S of NewEng on Christmas Day, and this possibility is expressed in some of the Ensemble members, the bottom line is that it's just going to be very difficult to bring the shortwave from TX to the East Coast in 24-36 hours given the slow-moving pattern that will be just beginning to break up. I've see the 12Z GFS and it's not a bad representation of what's appearing to be the most-likely scenario, which would be a coastal storm developing along a baroclinic zone S of NewEng, resulting in a rain south/snow central and north scenario that would be delayed until Christmas night or the day after Christmas. So, if I had to lay it on the line I'd expect a cool (not cold) and dry holiday for most of the daylight hours with rain and snow Christmas night into Tuesday. The reason I'm not yet laying that on the line is simple, in a very complicated way. ;) That is, I have a tremendous amount of respect for the atmospheric setup and its inherent unpredictability with nearby cold air (but not entrenched), hastening flow (but uncertainty on the rate at which it quickens), LOTS of energy all over the map including an interaction of shallow cold from Northern shortwaves needing to be timed perfectly with Srn stream vorts, and a confirmed moist flow (perhaps the most sure part of the equation). The moisture is a very important part of the equation, as any Srn stream vort max that does break away would certainly produce precip given its origins and the available Gulf and Pacific moisture, and the 12Z GGEM (Canadian) is one example of the result if a piece of energy is pulled northeast toward the confluent flow east of the Eastern Seaboard quicker than anticipated, which brings precip into Srn NewEng by the end of the day Christmas. Finally, let's learn from the recent guidance when it comes to deciding how much stock to put into each model run, and trust the synoptics here, which continue to tell us the pattern is favorable for storm development along the coast sometime centered around Monday. The lesson I speak of is that, anecdotally, If we look at what happened with the guidance products for this coming Sat rain event, we've seen a trend slower and slower thru the week that really is only gaining agreement among guidance now that we come close to a 72 hour window. I believe in this pattern that 72 hour window is going to be critical, which means we should tread lightly as meteorologists before commiting the public to any one scenario.

The suspense lingers.

Matt

Tuesday's Discussion:

2:05 PM: Shortwave evident on water vapor imagery dropping southeast across Ontario and Quebec will continue to move over NewEng and will continue to result in areal expansion and some intensification of snow showers in upslope favored regions. Elsewhere, downsloping has kept mostly clear skies for most of the day but that trend should reverse as vort max brings colder air aloft and instability increases as a result. Flurries are likely to carry farther east and southeast with passage of vort late afternoon and evening, though areas of max downsloping not likely to see much of significance. Expecting some clearing in area of NVA behind the vort max, but also noting large area of high low level RH over Upstate NY, and as warm advection begins overnight into Wed AM with shifting winds - esp at 850 mb - this area of clouds should migrate east into NewEng and snow showers will redevelop in western mountains. These clouds will likely carry thru Wrn and Central NewEng Tue night but also will probably advance in broken form to Eastern NH/MA by daybreak. The concern here is that warm advection continuing thru the day Wed - from -10 C to -1 C at 850 mb between 12Z and 00Z - will keep isentropic lift and thereby allow for more cloud maintenance than currently progged at both lower and mid levels. Therefore, have beefed up cloud cover for Wed and will hold temps similar to Tue readings as a result.

The clear trend has been to slow the upper low over the SW US as current upper level obs and satellite imagery show the jet has already lifted north of the circulation. That said, there have been rather obvious differences in the timing of ejecting this upper low northeast into the Great Lakes, and the effect of the responding moisture on NewEng. One key player in the advancement of associated moisture or lack thereof for NewEng is the passage of a shortwave during the day Thursday that will re-establish and lock in northwest flow through the mid-levels. This, combined with a strong shortwave pushing into the Pacific Northwest, will amplify the northern stream ridge on top of the upper low. Though this won't qualify as a Rex block, it does have some similarities with regard to the slowing of the pattern and the slowing of the progression of the upper low. This shortwave also will force a new shot of Canadian cool into NewEng on Thu, and with the ridge axis slow to move east, this will mean the cool air will hold on as long as possible. While the amount of warm advection ahead of the slow moving upper low will be sufficient to warm the profile too much for snow in Southern NewEng, oftentimes we see the mountains of NH and ME as particularly good candidates for holding the cold enuf to get snow from these events. This time, however, there is concern even that these areas may see more rain than anything as the extremely slow progression of the upper low will be reflected at the surface, and this means the amplified 850 mb ridge will follow its 500 mb counterpart, cresting over NewEng late Fri and thereby setting up a pattern favorable for warm advection with a southerly low level flow throughout NewEng. Though the new Operational Canadian certainly looks much more promising for Northern cold by holding a 1033 mb high just west of Maine on Sat, the Canadian Ensemble members largely place this bubble of high pressure north of ME while the GFS members aim northeast. The positioning of that anticyclone will be pivotal for the north country, but given the ridge axis progression, I'd have to believe holding the cold is really only most likely for parts of the Maine mountains thru Nrn ME and after viewing the 00Z runs tonight, if they lend support to this idea, will ammend fcst accordingly for Nrn Mountains this weekend. A big part of why I'm waiting here is the number of uncertainties in the model forecasts right now, ranging from handling of the low level cold to speed of northern stream shortwaves and the upper low to our west. With many of these disturbances zipping in off the Pacific and found in data-sparse areas of Canada, I don't expect much consistency and view the longwave pattern as a better tool for the weekend.

As for that longwave pattern, there is still great disagreement among the guidance even to this regard, but the middle of the road thinking at this point would be to take the next upper low this weekend and carry it to the Midwest around Srn IL by Sunday with additional energy rotating around the base of the trof farther south. At least equally important is the strength and southward penetration of the northern stream shortwave moving thru Ern Canada on Sun, which will dictate how far south Canadian high pressure builds for Mon. At this point, the Ensemble members that indicate a position of the upper low that I'm favoring also favor a farther southward penetration of the Canadian anticyclone into NewEng, forcing the frontal boundary over or just south of Southern NewEng later on the 24th into the 25th. With the upper low in the position indicated, this would mean moisture-laden pieces of energy would eject and develop waves along this frontal boundary, and yes, one would be timed for Christmas Day. The most recent guidance product to come in line with this is the GFS which has come around in its 12Z run, though if the synoptics truly play out exactly as the GFS has outlined, the storm should be stronger, have a bigger precip shield, and be farther north than what the model is predicting given the baroclinicity that would be present. But more important than the operational runs, as mentioned, is the longwave pattern, which will feature a battle of the Western Atlantic ridge and the Ern Canada trof, and though there is extremely limited deep cold, there is plenty of low level cold available and that will be made more available by the Ern Canada sfc anticyclone late this weekend, so at this point I'm not willing to discount the possibility of snow for at least some of NewEng. If I see a trend toward a clear dampening of the nrn stream shortwave, I would be more than ammenable to warming the forecast, but with the guidance trending stronger in the northern stream, that would be an uncomfortable concession to make.

The longer pattern has been addressed in the General Wx Summary, but in short the lack of deep cold indicates marginal precip events, but moisture-loaded Pacific origin storms, thru the end of 2006, with a trend toward troffing and stronger negative temp anomalies after the 1st of January, and a definite replenishment of the cold air source in the high latitudes and across Alaska. In these high latitudes, heights are already as low as 4750 dm on today's 500 mb analysis show that cooling is indeed poised to continue, and the El Nino jet is actually helping to build this cold very deep in the coming weeks, because there is no mechanism thus far to exchange it southward.

Matt

QUIET BUT COOLER WEATHER ENDS THE WEEK...RAIN BEGINS THE CHRISTMAS WEEKEND BUT SNOW COULD END IT

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

A ridge of high pressure continues to protect New England on Thursday, and will keep the six-state region dry through Friday, even though strong energetic disturbances continue to tear across the country. The blizzard that swept through the Rockies and Central Plains keeps the Denver airport closed as of this writing, and though it is now weakening, is still a moisture-loaded entity that is dropping heavy rains to the east of its path. This storm will only slowly meander northeast toward the Great Lakes as it bumps up against our protective, cool, dry dome of high pressure and fair weather. This weekend, as the pattern unlocks, storms will gain speed in their travels, and the presence of moisture, cold, warmth and energy all on a weather map featuring a shifting jet stream pattern will reduce certainty in forecasting and also put us in a pattern favoring new storm growth in the Eastern United States.

In the meantime, morning clouds across the southern half of New England have been eroding and will continue to give way to increasing sunshine as drier air aloft settles southward out of Canada. A weak cold front pushing south across Northern New England has been weakening, but winds have remained active on both sides of this front, gusting over 20 mph at times. The combination of increasing sunshine and a westerly "downsloping" wind coming off the mountains and hills of New England will help to warm the airmass for most areas - once again coming well above normal for the date with regard to daily high temperatures. The cool flow of air will be strengthened Thursday night as an upper level disturbance scoots east of New England, further assisting in tugging chill southward out of Canada.

Meanwhile, the major storm well to our west has helped to carve out a "trough", or a dip in the jet stream. As that dip in the fast flowing river of air flows across the Western and Central United States, here in the east we'll find a "ridge", or a bump in the jet stream that means the air will flow from south to north across the Eastern United States. Winds from the south deep in the atmosphere will favor Gulf of Mexico moisture being transported north, and the result will be thickening clouds with mild and moist air high in the sky spilling over our cool dome of air near the surface, then eventually developing rain by Saturday. That push of southern warmth will be too significant for wintry precipitation in much of New England, and it appears as though even the mountains of the north - while extreme Northern New Hampshire and the Mountains of Maine through Northern Maine may begin as a brief period of ice pellets - will see rain as the day wears on. In Southern New England, this rain probably will taper by dinnertime on Saturday, though it will hold on longer the farther north and east one travels.

At the beginning of this discussion, remember that I mentioned certainty would decrease later in the forecast period. The reasoning behind that statement is because we have so many components for storm formation that are available on the national weather map, and a rapidly changing jet stream pattern loaded with energetic disturbances blasting into the Pacific coast in an El Nino pattern. The most overwhelming trait of the atmosphere, however, in addition to the energetic pattern described above, is the lack of deep cold air available from Eastern Canada, and without deep cold, snow lovers truly are missing something reliable to hang their hat on. That said, there will be a few key players in the holiday weekend forecast that are the pillars of uncertainty in this pattern and keep the chances for snow alive, and they are as follows:

After Saturday's rain, there will be very little cold air available to wrap in behind the storm, winding up into James Bay, Canada, and merging with a Canadian disturbance over Hudson Bay. The merger of these two systems, however, will strengthen northwest winds aloft out of Central Canada, and this will sweep a strong upper level Canadian disturbance across the Northern Tier of the US, from the Great Lakes to New England Saturday night through Sunday. The origins of this new disturbance - racing out of Western and Central Canada - will result in a wake of cold air left behind as it swings through, likely bringing rain and snow showers later Sunday, especially to Northern New England, and ushering in marginally cold air to New England for Sunday night through Christmas Day - that is, air that would cool very close to a rain/snow threshold if saturated. Southern stream energy will be found over the Southern Plains Saturday night into Sunday, and this will be the impetus for moist storm development to our south on Christmas Day.

Keep in mind, though, that the jet stream winds aloft will favor blowing any storm toward the northeast, and that should be the case with this next system, as well. The trick here is that, at this point, it would appear as though any storm to affect New England would have to wait until Christmas night or Tuesday simply by virtue of the fact that it will take time for a significant piece of this energy, if not the entire disturbance itself, to traverse the expanse of land east of the Mississippi River and reach the Eastern Seaboard, and this would leave cool but mostly dry conditions on Christmas Day with a chance of rain or snow Monday night into Tuesday. I've seen increasing agreement among our guidance that this pattern should be the one to unfold, and this is the best forecast that can be put out right now.

Nonetheless, with a strong flow of winds southeast of New England Sunday into Monday, there is still a small potential that a piece of energy, rather than the entire chunk of energy, would break away and race south of New England ahead of schedule. Given that we'd be in cool air and Sunday's cold front would be just south of New England, this would mean the potential for snow earlier on Christmas Day, though at this point it would seem that simply the distance this disturbance has to travel - from Little Rock, Arkansas, to the Eastern Seaboard beginning its journey Saturday night - is just too great to arrive sooner. So, if we are to see some sunshine and a cool but mostly dry Christmas Day, this would allow temperatures to warm into the 40s for at least Southern New England. Air aloft, as mentioned above, would be only marginally cold, so it's conceivable that some areas would begin as rain, then have to changeover to snow as more cold air became involved and the lifting motion associated with cloud production also helped to cool the air. It also seems to make sense that in a marginally cold airmass with a warm ocean, there will be a well-pronounced rain/snow line, that may penetrate as far north as Southern New Hampshire or Northern Massachusetts at some point Christmas Night or on Tuesday. Again, though it seems like I'm laying out a detailed scenario here for the 25th/26th, I'd ask you to remember that this is a scenario that still is subject to large changes given the highly erratic pattern we remain in from Saturday onward.

Looking farther out, the pattern will remain quite active with a series of strong Pacific disturbances traversing the country for the next couple of weeks. This certainly raises the potential for a number of moist storms to affect the country, and with a persistent trough in the jet stream over the Eastern half of the U.S., the Eastern Seaboard would remain in the line of sight. That said, there are also no signs of any deep intrusion of cold air to the Northeast, which means each one of these moist events may walk the line between rain and snow until the end of the month. Thereafter, a few factors will combine to keep hopes of winter from completely fading - one will be the stronger establishment of an Eastern U.S. jet stream trough, which would allow near-normal air to spill southward for the start of the New Year, and a much stronger presence of deep cold from Alaska to Northern Canada, indicating the well of cold air will finally be refilling for the Western Hemisphere, which is something we've lacked of late.

Matt

Matt's Technical Meteorological Discussion: Updated Thursday, December 21 at 2:35 PM

Short term remains rather straight-forward tho winds will stay active overnight esp in Nrn NewEng, and this upslope flow combined with cold advection will bring increase llvl instability. Already have seen resulting cloud production along Canadian border this afternoon and expect this trend to continue southward with midlvl cooling, and this will result in mountain flurries and snow showers. Farther south, few clouds will blow thru but that should be about it.

Good agreement on dry Fri with increasing high altitude moisture after NW flow relaxes. Also good agreement on bringing precip in Fri night to most areas and after a trend toward significant slowing, speed has once again increased in the guidance so SW NewEng encompassed by Fri eve and just about all of NewEng encompassed overnight. This quicker onslaught of moisture in the guidance is part of the overall unpredictability of the pattern that's been discussed here the past couple of days with fast jet stream flow, tons of vorticity maximums and plenty of moisture available. The incoming moisture comes with increasing warmth in this case, and likelihood of evaporative cooling enuf for any frozen precip in the far Nrn mountains as mentioned yesterday has decreased to almost nil. Therefore, this will be a rain event for one and all. And it will be a heavy rain event! Good Gulf connection teams with strong PVA to really crank precip and good agreement among nearly all guidance of around 2" precip in rather large band of heaviest precip that will set up along path of 850 mb low center, where warm advection and isentropic lift is maximized, and this should be across CT, Cntrl/Wrn MA, Cntrl/Srn NH. Just about all areas can handle this rainfall without a problem - closest call is SCentral coast of CT where 6 and 12 hr flash flood guidance is around 2.5-2.75". No vegetative uptake will mean lots of runoff, but relatively dry antecedent conditions and no snow will mitigate. Shot of rain synoptically should come with warm advection, so Srn NewEng sees rain taper later Sat and Sat evening events - save for some dense fog - may be OK in Srn NewEng, esp the farther SW one is.

Of course, all eyes are on the latter period which I've described the past two days in as much detail as possible, though we've been waiting for confirmation of some of the details laid out here yesterday. Most of those details - especially the ones laid out here in the technical disc where you got a bit more of my inside thinking than in the General disc - seem to be coming together in the guidance so far (please reference previous disc below if you need a refresher). That is, the Sunday shortwave brings in marginal cold, the jet stream shifts S of New Eng Mon, and the next upper low needs to find a way from the Srn Plains to the East Coast of the US. It can find that way but it'll be tough to get it there by midday Christmas...still, one possibility discussed here yesterday still is on the table, which is to eject a piece of vorticity northeast into the confluent flow and develop a rather flat front-running wave that could deliver some precip to esp Srn NewEng on Christmas Day, but at that point the air may be just on the warm side of marginal and even if that happens it may come down as raindrops. Still, I see this as a low probability scenario, with the more likely scenario to wait until the more substantial energy shoots east, by which point a bubble high of llvl cold over SE Canada has been able to muscle cold air S, and this, aided by evaporational cooling, would help to make ptype snow in many areas Mon Ngt into Tue. With such a marginal airmass, and the precip type relying upon a relatively weak bubble high north of NewEng, there is likely to be a rain/snow line which - between the marginal airmass and still relatively warm ocean - may penetrate pretty far inland and north, even perhaps up to Central/Srn NH. But this is a detail that shouldn't be worked out now...there is still a great deal that can change between now and 12/25-26, so for now we'll stay focused on the pattern and getting this storm to form, then we can worry about the rest.

Go get your shopping done!

Matt

Wednesday's Discussion:

1:15 PM: A brief discussion today to address some key points to the coming forecast.

Quiet in the short term with temps tonight warmer than last thanks to increasing SW gradient flow and at least a few clouds that will traverse NewEng assoc with frontal boundary settling S across NewEng in response to shortwave traversing Ontario and Quebec. This boundary should sit over Srn NewEng most of Thu and midlvl thermal and theta-e gradient along with slight directional wind shift will be the impetus for cloud development in Central and Srn NewEng, shifting S thru the day as midlvl front sags southward. This will be a similar tho milder scenario to what is playing out over MN today with this shortwave. Dry low levels should preclude most precip, though a few flurries can't be entirely ruled out in Srn NewEng morning to midday.

Cool and dry air holds strong on Fri with NW flow leading into confluent flow E of NewEng as warm and moist advection works NE. Trend continues to be going slow on precip advancement for weekend storm, appearing more likely as a late Fri night into Sat start time. Tho 850 temps may go to near zero in NH and ME mountains, air still will be rather dry and wet bulb temp will be subzero so as precip moves in and atmosphere saturates we should see at least a period of snow in the Nrn NH/ME mountains, though warm advection wins the battle for most. From the mountains of Maine to Nrn ME, we may hold the cold just enough for a change from snow to sleet or freezing rain rather than rain. With triple point development likely, precip should be locally heavy in Central/Srn NewEng for part of Sat.

Farther out, my thinking from yesterday hasn't changed much, so for those of you who didn't have a chance to read I'll first direct you to the discussion below this one. What I do see happening is what I've tried to explain in layman's terms in the General Weather Summary above, which is this: Current upper low moves thru Great Lakes and merges with upper low over James Bay. This pivots Wrn Canada strong shortwave under the belly of these merged lows, ejecting in quickly E along the Canadian border and into NewEng later Sun. It will encounter air that won't be all that cold given the occlusion from Sat and the lack of any cold behind the storm to sweep in, so showers along the greatest PVA of Nrn NewEng still may be a mix of rain and snow latter half of Sun, but will end as snow showers with colder air streaming in behind the shortwave. Tho I still see the possibility of a piece of Srn energy ejecting sooner than anticipated and therefore passing S of NewEng on Christmas Day, and this possibility is expressed in some of the Ensemble members, the bottom line is that it's just going to be very difficult to bring the shortwave from TX to the East Coast in 24-36 hours given the slow-moving pattern that will be just beginning to break up. I've see the 12Z GFS and it's not a bad representation of what's appearing to be the most-likely scenario, which would be a coastal storm developing along a baroclinic zone S of NewEng, resulting in a rain south/snow central and north scenario that would be delayed until Christmas night or the day after Christmas. So, if I had to lay it on the line I'd expect a cool (not cold) and dry holiday for most of the daylight hours with rain and snow Christmas night into Tuesday. The reason I'm not yet laying that on the line is simple, in a very complicated way. ;) That is, I have a tremendous amount of respect for the atmospheric setup and its inherent unpredictability with nearby cold air (but not entrenched), hastening flow (but uncertainty on the rate at which it quickens), LOTS of energy all over the map including an interaction of shallow cold from Northern shortwaves needing to be timed perfectly with Srn stream vorts, and a confirmed moist flow (perhaps the most sure part of the equation). The moisture is a very important part of the equation, as any Srn stream vort max that does break away would certainly produce precip given its origins and the available Gulf and Pacific moisture, and the 12Z GGEM (Canadian) is one example of the result if a piece of energy is pulled northeast toward the confluent flow east of the Eastern Seaboard quicker than anticipated, which brings precip into Srn NewEng by the end of the day Christmas. Finally, let's learn from the recent guidance when it comes to deciding how much stock to put into each model run, and trust the synoptics here, which continue to tell us the pattern is favorable for storm development along the coast sometime centered around Monday. The lesson I speak of is that, anecdotally, If we look at what happened with the guidance products for this coming Sat rain event, we've seen a trend slower and slower thru the week that really is only gaining agreement among guidance now that we come close to a 72 hour window. I believe in this pattern that 72 hour window is going to be critical, which means we should tread lightly as meteorologists before commiting the public to any one scenario.

The suspense lingers.

Matt

Tuesday's Discussion:

2:05 PM: Shortwave evident on water vapor imagery dropping southeast across Ontario and Quebec will continue to move over NewEng and will continue to result in areal expansion and some intensification of snow showers in upslope favored regions. Elsewhere, downsloping has kept mostly clear skies for most of the day but that trend should reverse as vort max brings colder air aloft and instability increases as a result. Flurries are likely to carry farther east and southeast with passage of vort late afternoon and evening, though areas of max downsloping not likely to see much of significance. Expecting some clearing in area of NVA behind the vort max, but also noting large area of high low level RH over Upstate NY, and as warm advection begins overnight into Wed AM with shifting winds - esp at 850 mb - this area of clouds should migrate east into NewEng and snow showers will redevelop in western mountains. These clouds will likely carry thru Wrn and Central NewEng Tue night but also will probably advance in broken form to Eastern NH/MA by daybreak. The concern here is that warm advection continuing thru the day Wed - from -10 C to -1 C at 850 mb between 12Z and 00Z - will keep isentropic lift and thereby allow for more cloud maintenance than currently progged at both lower and mid levels. Therefore, have beefed up cloud cover for Wed and will hold temps similar to Tue readings as a result.

The clear trend has been to slow the upper low over the SW US as current upper level obs and satellite imagery show the jet has already lifted north of the circulation. That said, there have been rather obvious differences in the timing of ejecting this upper low northeast into the Great Lakes, and the effect of the responding moisture on NewEng. One key player in the advancement of associated moisture or lack thereof for NewEng is the passage of a shortwave during the day Thursday that will re-establish and lock in northwest flow through the mid-levels. This, combined with a strong shortwave pushing into the Pacific Northwest, will amplify the northern stream ridge on top of the upper low. Though this won't qualify as a Rex block, it does have some similarities with regard to the slowing of the pattern and the slowing of the progression of the upper low. This shortwave also will force a new shot of Canadian cool into NewEng on Thu, and with the ridge axis slow to move east, this will mean the cool air will hold on as long as possible. While the amount of warm advection ahead of the slow moving upper low will be sufficient to warm the profile too much for snow in Southern NewEng, oftentimes we see the mountains of NH and ME as particularly good candidates for holding the cold enuf to get snow from these events. This time, however, there is concern even that these areas may see more rain than anything as the extremely slow progression of the upper low will be reflected at the surface, and this means the amplified 850 mb ridge will follow its 500 mb counterpart, cresting over NewEng late Fri and thereby setting up a pattern favorable for warm advection with a southerly low level flow throughout NewEng. Though the new Operational Canadian certainly looks much more promising for Northern cold by holding a 1033 mb high just west of Maine on Sat, the Canadian Ensemble members largely place this bubble of high pressure north of ME while the GFS members aim northeast. The positioning of that anticyclone will be pivotal for the north country, but given the ridge axis progression, I'd have to believe holding the cold is really only most likely for parts of the Maine mountains thru Nrn ME and after viewing the 00Z runs tonight, if they lend support to this idea, will ammend fcst accordingly for Nrn Mountains this weekend. A big part of why I'm waiting here is the number of uncertainties in the model forecasts right now, ranging from handling of the low level cold to speed of northern stream shortwaves and the upper low to our west. With many of these disturbances zipping in off the Pacific and found in data-sparse areas of Canada, I don't expect much consistency and view the longwave pattern as a better tool for the weekend.

As for that longwave pattern, there is still great disagreement among the guidance even to this regard, but the middle of the road thinking at this point would be to take the next upper low this weekend and carry it to the Midwest around Srn IL by Sunday with additional energy rotating around the base of the trof farther south. At least equally important is the strength and southward penetration of the northern stream shortwave moving thru Ern Canada on Sun, which will dictate how far south Canadian high pressure builds for Mon. At this point, the Ensemble members that indicate a position of the upper low that I'm favoring also favor a farther southward penetration of the Canadian anticyclone into NewEng, forcing the frontal boundary over or just south of Southern NewEng later on the 24th into the 25th. With the upper low in the position indicated, this would mean moisture-laden pieces of energy would eject and develop waves along this frontal boundary, and yes, one would be timed for Christmas Day. The most recent guidance product to come in line with this is the GFS which has come around in its 12Z run, though if the synoptics truly play out exactly as the GFS has outlined, the storm should be stronger, have a bigger precip shield, and be farther north than what the model is predicting given the baroclinicity that would be present. But more important than the operational runs, as mentioned, is the longwave pattern, which will feature a battle of the Western Atlantic ridge and the Ern Canada trof, and though there is extremely limited deep cold, there is plenty of low level cold available and that will be made more available by the Ern Canada sfc anticyclone late this weekend, so at this point I'm not willing to discount the possibility of snow for at least some of NewEng. If I see a trend toward a clear dampening of the nrn stream shortwave, I would be more than ammenable to warming the forecast, but with the guidance trending stronger in the northern stream, that would be an uncomfortable concession to make.

The longer pattern has been addressed in the General Wx Summary, but in short the lack of deep cold indicates marginal precip events, but moisture-loaded Pacific origin storms, thru the end of 2006, with a trend toward troffing and stronger negative temp anomalies after the 1st of January, and a definite replenishment of the cold air source in the high latitudes and across Alaska. In these high latitudes, heights are already as low as 4750 dm on today's 500 mb analysis show that cooling is indeed poised to continue, and the El Nino jet is actually helping to build this cold very deep in the coming weeks, because there is no mechanism thus far to exchange it southward.

Matt

QUIET WEATHER TO ROUND OUT THE WEEK...MOSTLY RAIN LIKELY WITH SATURDAY STORM...HOLIDAY PATTERN REMAINS VOLATILE

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

Though the weather will remain quiet through the end of the workweek here in New England, strong energetic disturbances are traversing the nation. While New England began our Wednesday quiet but frosty, a strong, moisture-loaded storm in the nation's midsection is delivering a powerful winter blow to the Central Plains, and dropping heavy rains to the east of its path. This storm will only slowly meander northeast toward the Great Lakes as high pressure - fair weather - protects New England for a few days. This weekend, the pattern unlocks and storms gain speed in their travels, but the presence of moisture, cold, warmth and energy all on a weather map featuring a shifting jet stream pattern will reduce certainty in forecasting to a window of approximately 72-96 hours.

Interestingly enough, the next two and a half days of that time period will be realtively quiet here in New England. The cold start Wednesday morning put a thick frost on some car windshields before sunshine had a chance to melt it away, and the cool start has left a tall ladder to climb with regard to warming things up across New England. Nonetheless, sunshine will combine with a breeze that begins light from the northwest, but ends as an increasing southwest wind, to bring high temperatures close to or slightly above Tuesday's cool but pleasant and above normal values. Beginning Tuesday night, we'll all notice the impact of a strengthening southwest flow and the milder air moving in, as overnight low temperatures will be noticeably milder than Tuesday night's low, dipping below freezing in most spots but not likely to drop below the 20s in even our cooler communities. The combination of an active breeze and partly cloudy skies should also mean frost will be less thick than it was Wednesday morning.

Though the major storm on our national map will certainly be the one pulling from the Central Plains today through the Upper Great Lakes the remainder of this week, there will also be an active flow of disturbances across Central and Southern Canada. In fact, while our own nation's big storm stays west, it's these Canadian disturbances scooting quickly from west to east that will provide shots of cool air to New England every couple of days. The key here is that those who want to see snow need to see this cool air come in immediately prior to moisture, which thus far has not happened and seems unlikely to happen for our next shot of moisture on Saturday. In the meantime, a pronounced rebound of milder air on Thursday will bring temperatures to near 50 in a few warmer communities of Southern New England, but will precede one of the aforementioned shots of Canadian cool, meaning winds will shift and cooler air will once again settle over the six-state region later Thursday and especially Friday to end the workweek. Sky cover will be variable through the period, increased with the passage of an upper level disturbance and its associated cold front Thursday, then perhaps increasing aloft as milder air is thrown into the Northeast several thousand feet above our heads, in advance of the approaching and weakening storm that will have exhausted itself over the Midwest.

Though the storm will be weakening it will have already served to redirect the jet stream winds aloft - the fast river of air high in the sky that steers our storms and acts as a thermostat for the atmosphere, separating cold air to the north from warmer air to the south. In fact, as that storm churns across the nation's midsection, it's been pulling up record warmth ahead of it and record cold behind it, and that cold air has been helping to carve out a "trough", or a dip in the jet stream. As that dip in the fast flowing river of air flows across the Western and Central United States, here in the east we'll find a "ridge", or a bump in the jet stream that means the air will flow from south to north across the Eastern United States. Winds from the south deep in the atmosphere will favor Gulf of Mexico moisture being transported north, and the result will be thickening clouds with mild and moist air high in the sky spilling over our cool dome of air near the surface, then eventually developing rain by Saturday.

The type of precipitation with this storm - as with most of the other events of the next several days - will hinge upon how much cold air is present, and just how long that cold can hold on. At this point, it appears to me as though the push of southern warmth will be too significant for wintry precipitation in much of New England - especially Central and Southern areas - while the mountains of the north, and especially the mountains of Northern New Hampshire and Maine, may hold onto enough cold air to receive some snow at the start of the storm early Saturday, though even that will probably change to rain as the day wears on, though the mountains of Maine to Northern Maine will stand the best chance of holding onto cold enough air to keep snowflakes or sleet pellets falling. Periods of rain are likely to fall over most of New England on Saturday.

At the beginning of this discussion, remember that I mentioned accuracy decreases beyond 3 to 4 days in a pattern such as this. The reasoning behind that statement is because we have so many components for storm formation that are available on the national weather map, and a rapidly changing jet stream pattern loaded with energetic disturbances blasting into the Pacific coast in an El Nino pattern. I made mention of this reality numerous times in my broadcasts on Wednesday, as I feel it's important to explain why a map of Christmas Day can't be trusted from this far out, and in line with that thinking I did continue to illustrate the pattern for the holiday, but certainly not any specifics on storm formation - that information can be guessed at in this pattern, but not honestly and truthfully forecasted. I convey that point in this discussion, too, because it's important to understand that there are many possibilities still on the table for the holiday. The most overwhelming trait of the atmosphere, however, in addition to the energetic pattern described above, is the lack of deep cold air available from Eastern Canada, and without deep cold, snow lovers truly are missing something reliable to hang their hat on. That said, there will be a few key players in the holiday weekend forecast that are the pillars of uncertainty in this pattern, and they are as follows:

After Saturday's rain, there will be very little cold air available to wrap in behind the storm, winding up into James Bay, Canada, and merging with a Canadian disturbance over Hudson Bay. The merger of these two systems, however, will strengthen northwest winds aloft out of Central Canada, and this will sweep a strong upper level Canadian disturbance across the Northern Tier of the US, from the Great Lakes to New England Saturday night through Sunday. The origins of this new disturbance - racing out of Western and Central Canada - will result in a wake of cold air left behind the system as it swings through, likely bringing rain and snow showers later Sunday, especially to Northern New England, and ushering in marginally cold air to New England for Sunday night and Christmas Day - that is, air that would cool very close to a rain/snow threshold if saturated. The question here will be if that air will indeed be saturated by incoming moisture, and that depends on storm evolution or lack thereof. Southern stream energy will be found over the Southern Plains Saturday night into Sunday, and this will be the impetus for moist storm development. At this point, it would appear as though any storm to affect New England would have to wait until Christmas night or Tuesday simply by virtue of the fact that it will take time for a significant piece of this energy, if not the entire disturbance itself, to traverse the expanse of land east of the Mississippi River and reach the Eastern Seaboard, and this would leave cool but mostly dry conditions on Christmas Day with a chance of rain or snow Monday night into Tuesday.

So why not just lay that on the line? With a strong flow of winds southeast of New England Sunday into Monday, there is the potential that a piece of energy, rather than the entire chunk of energy, would break away and race south of New England ahead of schedule. Given that we'd be in cool air and Sunday's cold front would be just south of New England, this would mean the potential for snow. So, given the potential for a number of scenarios here, it's best not to come up with a deterministic forecast that will end up changing multiple times, and instead to continue to acknowledge and monitor a pattern with potential, while hedging our bets toward what appears to be a favored later development.

Looking farther out, the pattern will remain quite active with a series of strong Pacific disturbances traversing the country for the next couple of weeks. This certainly raises the potential for a number of moist storms to affect the country, and with a persistent trough in the jet stream over the Eastern half of the U.S., the Eastern Seaboard would remain in the line of sight. That said, there are also no signs of any deep intrusion of cold air to the Northeast, which means each one of these moist events may walk the line between rain and snow until the end of the month. Thereafter, a few factors will combine to keep hopes of winter from completely fading - one will be the stronger establishment of an Eastern U.S. jet stream trough, which would allow near-normal air to spill southward for the start of the New Year, and a much stronger presence of deep cold from Alaska to Northern Canada, indicating the well of cold air will finally be refilling for the Western Hemisphere, which is something we've lacked of late.

Matt

Matt's Technical Meteorological Discussion: Updated Wednesday, December 20 at 1:15 PM

A brief discussion today to address some key points to the coming forecast.

Quiet in the short term with temps tonight warmer than last thanks to increasing SW gradient flow and at least a few clouds that will traverse NewEng assoc with frontal boundary settling S across NewEng in response to shortwave traversing Ontario and Quebec. This boundary should sit over Srn NewEng most of Thu and midlvl thermal and theta-e gradient along with slight directional wind shift will be the impetus for cloud development in Central and Srn NewEng, shifting S thru the day as midlvl front sags southward. This will be a similar tho milder scenario to what is playing out over MN today with this shortwave. Dry low levels should preclude most precip, though a few flurries can't be entirely ruled out in Srn NewEng morning to midday.

Cool and dry air holds strong on Fri with NW flow leading into confluent flow E of NewEng as warm and moist advection works NE. Trend continues to be going slow on precip advancement for weekend storm, appearing more likely as a late Fri night into Sat start time. Tho 850 temps may go to near zero in NH and ME mountains, air still will be rather dry and wet bulb temp will be subzero so as precip moves in and atmosphere saturates we should see at least a period of snow in the Nrn NH/ME mountains, though warm advection wins the battle for most. From the mountains of Maine to Nrn ME, we may hold the cold just enough for a change from snow to sleet or freezing rain rather than rain. With triple point development likely, precip should be locally heavy in Central/Srn NewEng for part of Sat.

Farther out, my thinking from yesterday hasn't changed much, so for those of you who didn't have a chance to read I'll first direct you to the discussion below this one. What I do see happening is what I've tried to explain in layman's terms in the General Weather Summary above, which is this: Current upper low moves thru Great Lakes and merges with upper low over James Bay. This pivots Wrn Canada strong shortwave under the belly of these merged lows, ejecting in quickly E along the Canadian border and into NewEng later Sun. It will encounter air that won't be all that cold given the occlusion from Sat and the lack of any cold behind the storm to sweep in, so showers along the greatest PVA of Nrn NewEng still may be a mix of rain and snow latter half of Sun, but will end as snow showers with colder air streaming in behind the shortwave. Tho I still see the possibility of a piece of Srn energy ejecting sooner than anticipated and therefore passing S of NewEng on Christmas Day, and this possibility is expressed in some of the Ensemble members, the bottom line is that it's just going to be very difficult to bring the shortwave from TX to the East Coast in 24-36 hours given the slow-moving pattern that will be just beginning to break up. I've see the 12Z GFS and it's not a bad representation of what's appearing to be the most-likely scenario, which would be a coastal storm developing along a baroclinic zone S of NewEng, resulting in a rain south/snow central and north scenario that would be delayed until Christmas night or the day after Christmas. So, if I had to lay it on the line I'd expect a cool (not cold) and dry holiday for most of the daylight hours with rain and snow Christmas night into Tuesday. The reason I'm not yet laying that on the line is simple, in a very complicated way. ;) That is, I have a tremendous amount of respect for the atmospheric setup and its inherent unpredictability with nearby cold air (but not entrenched), hastening flow (but uncertainty on the rate at which it quickens), LOTS of energy all over the map including an interaction of shallow cold from Northern shortwaves needing to be timed perfectly with Srn stream vorts, and a confirmed moist flow (perhaps the most sure part of the equation). The moisture is a very important part of the equation, as any Srn stream vort max that does break away would certainly produce precip given its origins and the available Gulf and Pacific moisture, and the 12Z GGEM (Canadian) is one example of the result if a piece of energy is pulled northeast toward the confluent flow east of the Eastern Seaboard quicker than anticipated, which brings precip into Srn NewEng by the end of the day Christmas. Finally, let's learn from the recent guidance when it comes to deciding how much stock to put into each model run, and trust the synoptics here, which continue to tell us the pattern is favorable for storm development along the coast sometime centered around Monday. The lesson I speak of is that, anecdotally, If we look at what happened with the guidance products for this coming Sat rain event, we've seen a trend slower and slower thru the week that really is only gaining agreement among guidance now that we come close to a 72 hour window. I believe in this pattern that 72 hour window is going to be critical, which means we should tread lightly as meteorologists before commiting the public to any one scenario.

The suspense lingers.

Matt

Tuesday's Discussion:

2:05 PM: Shortwave evident on water vapor imagery dropping southeast across Ontario and Quebec will continue to move over NewEng and will continue to result in areal expansion and some intensification of snow showers in upslope favored regions. Elsewhere, downsloping has kept mostly clear skies for most of the day but that trend should reverse as vort max brings colder air aloft and instability increases as a result. Flurries are likely to carry farther east and southeast with passage of vort late afternoon and evening, though areas of max downsloping not likely to see much of significance. Expecting some clearing in area of NVA behind the vort max, but also noting large area of high low level RH over Upstate NY, and as warm advection begins overnight into Wed AM with shifting winds - esp at 850 mb - this area of clouds should migrate east into NewEng and snow showers will redevelop in western mountains. These clouds will likely carry thru Wrn and Central NewEng Tue night but also will probably advance in broken form to Eastern NH/MA by daybreak. The concern here is that warm advection continuing thru the day Wed - from -10 C to -1 C at 850 mb between 12Z and 00Z - will keep isentropic lift and thereby allow for more cloud maintenance than currently progged at both lower and mid levels. Therefore, have beefed up cloud cover for Wed and will hold temps similar to Tue readings as a result.

The clear trend has been to slow the upper low over the SW US as current upper level obs and satellite imagery show the jet has already lifted north of the circulation. That said, there have been rather obvious differences in the timing of ejecting this upper low northeast into the Great Lakes, and the effect of the responding moisture on NewEng. One key player in the advancement of associated moisture or lack thereof for NewEng is the passage of a shortwave during the day Thursday that will re-establish and lock in northwest flow through the mid-levels. This, combined with a strong shortwave pushing into the Pacific Northwest, will amplify the northern stream ridge on top of the upper low. Though this won't qualify as a Rex block, it does have some similarities with regard to the slowing of the pattern and the slowing of the progression of the upper low. This shortwave also will force a new shot of Canadian cool into NewEng on Thu, and with the ridge axis slow to move east, this will mean the cool air will hold on as long as possible. While the amount of warm advection ahead of the slow moving upper low will be sufficient to warm the profile too much for snow in Southern NewEng, oftentimes we see the mountains of NH and ME as particularly good candidates for holding the cold enuf to get snow from these events. This time, however, there is concern even that these areas may see more rain than anything as the extremely slow progression of the upper low will be reflected at the surface, and this means the amplified 850 mb ridge will follow its 500 mb counterpart, cresting over NewEng late Fri and thereby setting up a pattern favorable for warm advection with a southerly low level flow throughout NewEng. Though the new Operational Canadian certainly looks much more promising for Northern cold by holding a 1033 mb high just west of Maine on Sat, the Canadian Ensemble members largely place this bubble of high pressure north of ME while the GFS members aim northeast. The positioning of that anticyclone will be pivotal for the north country, but given the ridge axis progression, I'd have to believe holding the cold is really only most likely for parts of the Maine mountains thru Nrn ME and after viewing the 00Z runs tonight, if they lend support to this idea, will ammend fcst accordingly for Nrn Mountains this weekend. A big part of why I'm waiting here is the number of uncertainties in the model forecasts right now, ranging from handling of the low level cold to speed of northern stream shortwaves and the upper low to our west. With many of these disturbances zipping in off the Pacific and found in data-sparse areas of Canada, I don't expect much consistency and view the longwave pattern as a better tool for the weekend.

As for that longwave pattern, there is still great disagreement among the guidance even to this regard, but the middle of the road thinking at this point would be to take the next upper low this weekend and carry it to the Midwest around Srn IL by Sunday with additional energy rotating around the base of the trof farther south. At least equally important is the strength and southward penetration of the northern stream shortwave moving thru Ern Canada on Sun, which will dictate how far south Canadian high pressure builds for Mon. At this point, the Ensemble members that indicate a position of the upper low that I'm favoring also favor a farther southward penetration of the Canadian anticyclone into NewEng, forcing the frontal boundary over or just south of Southern NewEng later on the 24th into the 25th. With the upper low in the position indicated, this would mean moisture-laden pieces of energy would eject and develop waves along this frontal boundary, and yes, one would be timed for Christmas Day. The most recent guidance product to come in line with this is the GFS which has come around in its 12Z run, though if the synoptics truly play out exactly as the GFS has outlined, the storm should be stronger, have a bigger precip shield, and be farther north than what the model is predicting given the baroclinicity that would be present. But more important than the operational runs, as mentioned, is the longwave pattern, which will feature a battle of the Western Atlantic ridge and the Ern Canada trof, and though there is extremely limited deep cold, there is plenty of low level cold available and that will be made more available by the Ern Canada sfc anticyclone late this weekend, so at this point I'm not willing to discount the possibility of snow for at least some of NewEng. If I see a trend toward a clear dampening of the nrn stream shortwave, I would be more than ammenable to warming the forecast, but with the guidance trending stronger in the northern stream, that would be an uncomfortable concession to make.

The longer pattern has been addressed in the General Wx Summary, but in short the lack of deep cold indicates marginal precip events, but moisture-loaded Pacific origin storms, thru the end of 2006, with a trend toward troffing and stronger negative temp anomalies after the 1st of January, and a definite replenishment of the cold air source in the high latitudes and across Alaska. In these high latitudes, heights are already as low as 4750 dm on today's 500 mb analysis show that cooling is indeed poised to continue, and the El Nino jet is actually helping to build this cold very deep in the coming weeks, because there is no mechanism thus far to exchange it southward.

Matt

CHILLY WINDS LEAD NEW ENGLAND INTO MIDWEEK...MARGINAL TEMPERATURES DOMINATE THE WEATHER PATTERN FOR EACH STORM THROUGH 2006...COLD AIR WELL TO REFILL IN CANADA WITH TIME

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

Cooler air has taken hold of New England, and active breezes will continue to add a bite to the air throughout the day Tuesday. Meanwhile, a series of strong Pacific disturbances are churning across the United States as the Northeast sits under the jet stream winds aloft. Remember that these jet stream winds are the corridor of fast-moving air thousands of feet in altitude that steers our storm systems and acts as a thermostat for the atmosphere, separating cold air to the north from warmer air to the south. With this atmospheric thermostat running so close to New England, important swings in temperature will occur over the course of the next several days. The importance of these temperature swings comes because the timing of moisture with each shot of cold or warm air will determine precipitation type for each disturbance that moves through, extending out beyond the Christmas holiday.

There's no question a shot of chilly Canadian air has moved into New England for our Tuesday, though this comes with a drying atmosphere, as well, as clouds can be seen departing and diminishing south of New England on satellite imagery. Clouds do linger across Northern New England - at least in the mountains - where snow showers will continue thanks to a process called "upslope flow," where wind pushes against the mountain faces, is forced upward, cools quickly as it rises, and results in condensation and cloud formation. With a northwest wind gusting at times to over 20 mph Tuesday, this also means that areas south and east of the mountains are seeing "downsloping winds," which come down the mountain sides and favor drying rather than clouds. Therefore, plenty of sun will mix with scattered clouds in many areas away from the mountains. Even still, very cold air several thousand feet above our heads is likely to prompt at least some cloud development for one and all by the end of Tuesday afternoon, and even away from the mountains a few of these clouds may grow heavy enough to drop an isolated flurry.

As winds slacken a bit, temperatures will fall handily overnight Tuesday night with colder spots into the teens and most of the rest of us in the 20s. Though skies will begin partly cloudy - and likely will clear for a time, remaining clear in some eastern areas - a patch of low-altitude clouds will gradually migrate east out of New York State and into especially Western and Central New England later Tuesday night, bringing a few snow showers with them, especially in the western hills and mountains. With the center of an expansive high pressure cell shifting east from the Midwest to the Ohio Valley, and then the Mid-Atlantic coast, over the next 36 hours, the clockwise flow of air around this fair weather center will bring a west and southwest wind into New England on Wednesday. This wind will slowly but surely filter milder air into New England, and the clash between incoming mild air and lingering chill may allow for some of the aforementioned clouds to linger longer than they otherwise would across New England on Wednesday, filtering or blotting out the sun from time to time.

The jet stream winds - so crucial to the forecast - will continue shifting over the course of the week. To our west, a deep storm churning across the Central Plains at midweek, bringing heavy snow to the foothills of the Rockies and heavy icing to parts of Western Kansas, will tap moisture and warmth from the Gulf of Mexico as cold air surges southward on the west side of the counter-clockwise circulation. The result will be a steady progression of warm and moist air aloft later Thursday, bringing increasing high-altitude clouds to filter sunshine, but not a deep enough surge of moisture to produce any precipitation during the day Thursday as the primary storm center will still be located well to our west. Gradually, this slow-moving storm will feel the influence of the strong westerly jet stream winds, and after meandering across the Rockies, will begin to lift northeast. The main slug of energy associated with this storm will move across the Great Lakes and into Southern Canada for the end of the week, but ahead of this storm the jet stream winds will orient out of the Gulf of Mexico, delivering enough moisture for a shot of precipitation later Friday into Saturday.

Late Friday/Saturday precipitation - like the other events of the next several days - will hinge upon how much cold air is present, and just how long that cold can hold on. At this point, it appears to me as though the push of southern warmth will be too significant for wintry precipitation in much of New England - especially Central and Southern areas - while the mountains of the north, and especially the mountains of Northern New Hampshire and Maine, may hold onto enough cold air to receive some snow to start the weekend. By the time this disturbance moves into Canada and weakens, two important reactions will already be underway. The first is for a slug of cool air to migrate southeast out of Canada in the lower several thousand feet of the atmosphere and into New England for the upcoming weekend. The second will be for yet another strong upper level storm and its associated surface low pressure center to move across the Southwestern United States, the Rockies, and the Plains. This next storm will be one to watch, as it will move east into a trough - a dip in the jet stream winds aloft - over the Central United States that will favor continued development of this storm as it shifts east, pickup up Gulf Moisture. Because the jet stream trough is a dip in the winds, winds flow from the north, behind the trough, and from the south ahead of it. This is important, because it means any storms and moisture over the Southeastern United States later this weekend would be ushered northeast, pushed by these winds blowing from the south and therefore directed up the coastline. Once again it will be a battle of incoming warmth and moisture, and antecedent cold - should the cold hold on long enough, snow would be the result Christmas Day. Working in favor of snow will be a bubble of Canadian high pressure settling over Southeastern Canada over the weekend that will hold into ealry next week. When we examine all of these factors, it becomes evident that the ingredients are at least there for a Christmas snow that would certainly seem a miracle given the weather pattern of late. That said, I would caution one and all to take this as something that allows us to keep the fingers crossed and realize that there is still hope of a White Christmas - but I also would urge everyone to use extreme caution in trusting any offer of a blow-by-blow detailed account of whether it will be no storm, rain storm, snow storm, or otherwise. The honest answer here has to be that the atmosphere will be chaotic and will favor storm development with cold air nearby, but the level of interaction between Gulf Moisture and cold air will become clearer only with time.

Looking farther out, the pattern will remain quite active with a series of strong Pacific disturbances traversing the country for the next couple of weeks. This certainly raises the potential for a number of moist storms to affect the country, and with a persistent trough in the jet stream over the Eastern half of the U.S., the Eastern Seaboard would remain in the line of sight. That said, there are also no signs of any deep intrusion of cold air to the Northeast, which means each one of these moist events may walk the line between rain and snow until the end of the month. Thereafter, a few factors will combine to keep hopes of winter from completely fading - one will be the stronger establishment of an Eastern U.S. jet stream trough, which would allow near-normal air to spill southward for the start of the New Year, and a much stronger presence of deep cold from Alaska to Northern Canada, indicating the well of cold air will finally be refilling for the Western Hemisphere, which is something we've lacked of late.

Matt

Matt's Technical Meteorological Discussion: Updated Tuesday, December 19 at 2:05 PM

Shortwave evident on water vapor imagery dropping southeast across Ontario and Quebec will continue to move over NewEng and will continue to result in areal expansion and some intensification of snow showers in upslope favored regions. Elsewhere, downsloping has kept mostly clear skies for most of the day but that trend should reverse as vort max brings colder air aloft and instability increases as a result. Flurries are likely to carry farther east and southeast with passage of vort late afternoon and evening, though areas of max downsloping not likely to see much of significance. Expecting some clearing in area of NVA behind the vort max, but also noting large area of high low level RH over Upstate NY, and as warm advection begins overnight into Wed AM with shifting winds - esp at 850 mb - this area of clouds should migrate east into NewEng and snow showers will redevelop in western mountains. These clouds will likely carry thru Wrn and Central NewEng Tue night but also will probably advance in broken form to Eastern NH/MA by daybreak. The concern here is that warm advection continuing thru the day Wed - from -10 C to -1 C at 850 mb between 12Z and 00Z - will keep isentropic lift and thereby allow for more cloud maintenance than currently progged at both lower and mid levels. Therefore, have beefed up cloud cover for Wed and will hold temps similar to Tue readings as a result.

The clear trend has been to slow the upper low over the SW US as current upper level obs and satellite imagery show the jet has already lifted north of the circulation. That said, there have been rather obvious differences in the timing of ejecting this upper low northeast into the Great Lakes, and the effect of the responding moisture on NewEng. One key player in the advancement of associated moisture or lack thereof for NewEng is the passage of a shortwave during the day Thursday that will re-establish and lock in northwest flow through the mid-levels. This, combined with a strong shortwave pushing into the Pacific Northwest, will amplify the northern stream ridge on top of the upper low. Though this won't qualify as a Rex block, it does have some similarities with regard to the slowing of the pattern and the slowing of the progression of the upper low. This shortwave also will force a new shot of Canadian cool into NewEng on Thu, and with the ridge axis slow to move east, this will mean the cool air will hold on as long as possible. While the amount of warm advection ahead of the slow moving upper low will be sufficient to warm the profile too much for snow in Southern NewEng, oftentimes we see the mountains of NH and ME as particularly good candidates for holding the cold enuf to get snow from these events. This time, however, there is concern even that these areas may see more rain than anything as the extremely slow progression of the upper low will be reflected at the surface, and this means the amplified 850 mb ridge will follow its 500 mb counterpart, cresting over NewEng late Fri and thereby setting up a pattern favorable for warm advection with a southerly low level flow throughout NewEng. Though the new Operational Canadian certainly looks much more promising for Northern cold by holding a 1033 mb high just west of Maine on Sat, the Canadian Ensemble members largely place this bubble of high pressure north of ME while the GFS members aim northeast. The positioning of that anticyclone will be pivotal for the north country, but given the ridge axis progression, I'd have to believe holding the cold is really only most likely for parts of the Maine mountains thru Nrn ME and after viewing the 00Z runs tonight, if they lend support to this idea, will ammend fcst accordingly for Nrn Mountains this weekend. A big part of why I'm waiting here is the number of uncertainties in the model forecasts right now, ranging from handling of the low level cold to speed of northern stream shortwaves and the upper low to our west. With many of these disturbances zipping in off the Pacific and found in data-sparse areas of Canada, I don't expect much consistency and view the longwave pattern as a better tool for the weekend.

As for that longwave pattern, there is still great disagreement among the guidance even to this regard, but the middle of the road thinking at this point would be to take the next upper low this weekend and carry it to the Midwest around Srn IL by Sunday with additional energy rotating around the base of the trof farther south. At least equally important is the strength and southward penetration of the northern stream shortwave moving thru Ern Canada on Sun, which will dictate how far south Canadian high pressure builds for Mon. At this point, the Ensemble members that indicate a position of the upper low that I'm favoring also favor a farther southward penetration of the Canadian anticyclone into NewEng, forcing the frontal boundary over or just south of Southern NewEng later on the 24th into the 25th. With the upper low in the position indicated, this would mean moisture-laden pieces of energy would eject and develop waves along this frontal boundary, and yes, one would be timed for Christmas Day. The most recent guidance product to come in line with this is the GFS which has come around in its 12Z run, though if the synoptics truly play out exactly as the GFS has outlined, the storm should be stronger, have a bigger precip shield, and be farther north than what the model is predicting given the baroclinicity that would be present. But more important than the operational runs, as mentioned, is the longwave pattern, which will feature a battle of the Western Atlantic ridge and the Ern Canada trof, and though there is extremely limited deep cold, there is plenty of low level cold available and that will be made more available by the Ern Canada sfc anticyclone late this weekend, so at this point I'm not willing to discount the possibility of snow for at least some of NewEng. If I see a trend toward a clear dampening of the nrn stream shortwave, I would be more than ammenable to warming the forecast, but with the guidance trending stronger in the northern stream, that would be an uncomfortable concession to make.

The longer pattern has been addressed in the General Wx Summary, but in short the lack of deep cold indicates marginal precip events, but moisture-loaded Pacific origin storms, thru the end of 2006, with a trend toward troffing and stronger negative temp anomalies after the 1st of January, and a definite replenishment of the cold air source in the high latitudes and across Alaska. In these high latitudes, heights are already as low as 4750 dm on today's 500 mb analysis show that cooling is indeed poised to continue, and the El Nino jet is actually helping to build this cold very deep in the coming weeks, because there is no mechanism thus far to exchange it southward.

Matt

MONDAY SHOWERS TO BRING TUESDAY CHILL...HOLIDAY PATTERN CONTINUES TO HOLD POTENTIAL

Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes

General Weather Summary:

A series of strong Pacific disturbances will churn across the United States in the next several days. Meanwhile, shallow cold air continues to build across Southern Canada while the Northeastern United States sits under the fast jet stream winds aloft. Remember that these jet stream winds are the corridor of fast-moving air that steers our storm systems and acts as a thermostat for the atmosphere, separating cold air to the north from warmer air to the south. With this atmospheric thermostat running so close to New England, significant swings in temperature are likely over the course of the next several days. The timing of moisture with each shot of cold or warm air will determine precipitation type for each disturbance that moves through, extending out beyond the Christmas holiday.

Clearly, Monday's disturbance comes with enough mild air for raindrops in most areas. This upper level disturbance was zipping east through the day, and will move out of most of New England by mid-afternoon Monday, leaving most of Central and Southern New England under plenty of clouds, while Northern New England sees a continued blend of clouds and sun. The weather setup features a cold front sagging south through New England - draped over Central Massachusetts Monday morning - with cooler air gradually nosing southward behind the front, and mild air still in place in advance of it. A weak wave of low pressure along the front - the surface reflection of the aforementioned upper level disturbance - has helped to focus showers, and the passage of this wave and its associated upper level feature will help to yank heartier cold air southward from Canada. The result will be a freshening wind Monday evening.

Winds will remain quite active Monday night as a new, cool Canadian airmass spills south, dropping temperatures into the 20s for most locales and near 30 in Southeastern New England. Combined with 10-15 mph winds and a few higher gusts, these falling temperatures will help to produce wind chill values in the teens for many areas, making for a chilly night for those at work outside during the overnight. The shot of cool air will still be present on Tuesday, as temperatures struggle to rise out of the 30s in even the warmer locales, while thousands of feet above our heads an energetic disturbance will dive southeast across the region, prompting scattered snow showers through the day regionwide.

The jet stream winds - so crucial to the forecast - will coil and recoil over the course of the week, favoring a continued shot of cool air on Wednesday, and with a lack of any strong disturbances, likely plenty of sunshine mixed only with high altitude clouds. To our west, a deep storm will churn across the Central Plains and the counterclockwise flow around this storm both at the surface and aloft will usher moisture out of the Gulf of Mexico, and pull warmth northward, while cold air will surge south behind the storm center. The result will be an onslaught of warm and moist air aloft later Thursday, bringing increasing and thickening clouds to filter sunshine, but likely not a deep enough surge of moisture to produce any precipitation during the day Thursday as the primary storm center will still be located well to our west. Nonetheless, this storm will have left quite a mark across the Rocky Mountains, producing heavy snow in the foothills of the Rockies and even in Western Kansas. Gradually, this slow-moving storm will feel the influence of the strong westerly jet stream winds, and after meandering across the Rockies, will begin to lift northeast. The main slug of energy associated with this storm will move across the Great Lakes and into Southern Canada for the end of the week, but ahead of this storm the jet stream winds will orient out of the Gulf of Mexico, delivering first the clouds on Thursday, then a shot of precipitation on Friday.

Friday's precipitation - like the other events of the next several days - will hinge upon how much cold air is present, and just how long that cold can hold on. At this point, it appears to me as though the push of southern warmth will be too significant for wintry precipitation in much of New England - especially Central and Southern areas - while the mountains of the north, and especially the mountains of Northern New Hampshire and Maine, may hold onto enough cold air to receive some snow on Friday. By the time this disturbance moves into Canada and weakens, two important reactions will already be underway. The first is for a slug of cold air to migrate southeast out of Canada in the lower several thousand feet of the atmosphere and into New England for the upcoming weekend. The second will be for yet another strong upper level storm and its associated surface low pressure center to move across the Southwestern United States, the Rockies, and the Plains. This next storm will be one to watch, as it will move east into a trough - a dip in the jet stream winds aloft - over the Central United States that will favor continued development of this storm as it shifts east, pickup up Gulf Moisture. Because the jet stream trough is a dip in the winds, winds flow from the north, behind the trough, and from the south ahead of it. This is important, because it means any storms and moisture over the Southeastern United States later this weekend would be ushered northeast, pushed by these winds blowing from the south and therefore directed up the coastline. Once again it will be a battle of incoming warmth and moisture, and antecedent cold - should the cold hold on long enough, snow would be the result Christmas Day. Working in favor of snow will be a bubble of Canadian high pressure settling over Southeastern Canada over the weekend that will hold into ealry next week. When we examine all of these factors, it becomes evident that the ingredients are at least there for a Christmas snow that would certainly seem a miracle given the weather pattern of late. That said, I would caution one and all to take this as something that allows us to keep the fingers crossed, etc., etc., and I would urge everyone to use extreme caution when offered a blow-by-blow detailed account of whether it will be no storm, rain storm, snow storm, or otherwise. The honest answer here has to be that the atmosphere will be chaotic and will favor storm development with cold air nearby, but the level of interaction between Gulf Moisture and cold air will become clearer only with time. So...keep those fingers crossed and I'll see you back here and on NECN tomorrow.

Technical Discussion: Public appearance today, techie out tomorrow.

Matt

MATTNOYES.NET - Weather Website & Blog

Your Simple Source to Complex Weather - Daily Forecast, Discussion and Links For New England and Beyond!

December 2006

Friday, December 29, 2006

A BIT OF SATURDAY SNOW, SUN TO END 2006, AND A WINTRY MIX TO RING IN THE NEW YEAR

Thursday, December 28, 2006

REINFORCING CHILL TONIGHT...WEAK DISTURBANCE FOR SOME SNOW AND RAIN ON SATURDAY...ANOTHER BLIZZARD TO SLAM DENVER WILL BE WATCHED HERE BY NEW YEAR'S DAY

Wednesday, December 27, 2006

VARYING CLOUDS BUT NO MAJOR NEW ENGLAND STORMS FOR NEXT FEW DAYS...

Tuesday, December 26, 2006

THICK FOG FAR SOUTH, SNOW FAR NORTH, GRAY AND RATHER DULL IN BETWEEN

Monday, December 25, 2006

NO SNOW TO GREET US CHRISTMAS DAY...BUT CHRISTMAS NIGHT SHOWS SNOW ON THE WAY! FOR SOME.

Friday, December 22, 2006

"HO, HO, HO! NOW WHERE'S ALL MY SNOW?"

Thursday, December 21, 2006

QUIET BUT COOLER WEATHER ENDS THE WEEK...RAIN BEGINS THE CHRISTMAS WEEKEND BUT SNOW COULD END IT

Wednesday, December 20, 2006

QUIET WEATHER TO ROUND OUT THE WEEK...MOSTLY RAIN LIKELY WITH SATURDAY STORM...HOLIDAY PATTERN REMAINS VOLATILE

Tuesday, December 19, 2006

CHILLY WINDS LEAD NEW ENGLAND INTO MIDWEEK...MARGINAL TEMPERATURES DOMINATE THE WEATHER PATTERN FOR EACH STORM THROUGH 2006...COLD AIR WELL TO REFILL IN CANADA WITH TIME

Monday, December 18, 2006

MONDAY SHOWERS TO BRING TUESDAY CHILL...HOLIDAY PATTERN CONTINUES TO HOLD POTENTIAL

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