THANKSGIVING WEEK TO FEATURE BRUSH WITH COASTAL STORM FOR SOME...PERIODS OF DELIGHTFUL WEATHER AT TIMES
AS COOL AIR ESCAPES FROM CANADA, STUBBORN GRAY SKIES FOR MOST

REPEATED TUGS OF COLD AIR TO BRING PERIODS OF GRAY...BUT COULD GRAY + COLD = WHITE GROUND BY FRIDAY NIGHT?

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 [email protected].  This blog is for you, so I hope you enjoy it!  -Matt Noyes

General Weather Summary:

Welcome back to the blog!  After nearly 5" of rain with the Turkey Day storm, and sustained winds to between 40 and 50 mph near the coastline of Southern New England, the weekend brought drying and pleasant conditions to most of the six-state region.  The upcoming week will bring a gradual breakdown of the mild conditions as cold air settles southward in surges - one surge for Tuesday into midweek, and another likely by the upcoming weekend.

In the meantime, the jet stream winds aloft that steer our storms and act as a thermostat for the atmosphere have been dipping into a trough across the Western United States, and rising as a ridge here in the East.  The result has been to keep New England on the warm side of the atmospheric thermostat, and at the surface, an area of high pressure parked over the Appalachian Mountains is playing a role, as well - it's clockwise circulation of air around its center will send light southwest winds and slightly warmer air seeping into New England on Monday.  The combination of mild air and dimmed sunshine through milky skies shrouded with high-altitude cirrus clouds will push temperatures near 60 in Central and Southern New England.  Farther north, the southern edge of deep Canadian cold ensures such mild air will not arrive to the Canadian border.  In fact, with a strengthening and southward shifting northern high pressure cell moving across Hudson Bay into Southern Quebec over the next few days, cold air will be forced farther southward.

The passage of an upper level disturbance later Monday into Monday night across the Canadian border will team with the leading edge to this new cold air to spawn an area of snow across Central and Northern Maine, where a dusting is possible in the valleys around Bangor by Tuesday morning, an inch especially on grassy surfaces in higher terrain, and one to two inches from Millinocket points north, and up to three inches in the higher terrain of Aroostook County, ME.  Elsewhere, expect clouds to continue to thicken Monday night as the leading edge to the deeper Canadian cold will settle farther south into Central New England, marked by a shift in the winds to blow from the northeast, perhaps with a brief gust to over 20 mph.

As this wind shift - a cold front - settles southward through the day on Tuesday, the cool air welled up over Quebec will take a stronger hold of New England, and in some Southern New England locales, temperatures actually may fall during the day Tuesday after being kept rather mild by a blanket of overnight cloud cover.  By the end of Tuesday, most of New England will average around 40 degrees with a very raw feel made all that much more brisk by an active northeast wind, lots of clouds, and a few patches of drizzle and light showers by day's end.  The raw conditions are expected to continue on Wednesday, as warmer air moves in thousands of feet above our heads but makes little difference here on the ground, where dense cool air will remain firmly in place.  The clash between these two airmasses is likely to continue producing patches of drizzle and light rain showers through the day, especially in Southern and Central New England.

Meanwhile, though midweek will bring raw but relatively quiet conditions to New England, the active jet stream trough to our west will still be breeding storms across the nation's midsection.  As each of these storms wind up into the Great Lakes with wind, rain and snow, pieces of energy will break northeastward into Canada, riding north of New England over the jet stream ridge as new energy is repeatedly fed into the Rockies and Plains from the Pacific Ocean.  Meanwhile, a weaker feed of energy and moisture will develop along the Eastern Seaboard, gradually filtering increasing moisture northward from the Gulf of Mexico and Southeastern coastal waters, and increasing the threat for showers - while gradually moderating temperatures - for Thursday.

By later Thursday into Friday, the much stronger lobes of energy across the Plains States - feeding off the clash of deep Northern cold and deep Southern warmth and humidity - will organize into a new, strong, end-of week storm.  This storm will sweep from the Central Plains to the Canadian border of New England, swinging a cold front and its associated slug of rain through New England later Thursday through Thursday night.  The question - and it's an important one - is how quickly this front swings through the six-state region.  Though meteorological guidance products range from a quick progression, bringing cold air in for Friday, to a slow trudge, keeping mild air around until Friday night, the weather pattern would dictate the quicker surge of cold is more likely, and this would be important for a Friday night disturbance that would still need to swing through.  There are two reasons for the pattern favoring more cold into New England on Friday: 1) The amount of cold built up across Central and Southern Canada is quite heavy and dense, and the past two weeks has been eager to sag southward (remember 30s and rain last week, and the cool forecast for this midweek) and there is no sign that this cold will be any less dense or any less able to slide southward.  2) The jet stream winds aloft will converge just east of New England - that is, air will come together thousands of feet above our heads.  When air comes together aloft, it sinks through the atmosphere, favoring high pressure and therefore favoring a tug of cold air from Canada.

With the aforementioned active Pacific pattern continuing to bring energetic and rather moist disturbances across the country, there will be a weak to moderate disturbance caught in the jet stream winds aloft over the Ohio and Tennessee Valleys, and the jet stream will steer this disturbance south of New England later Friday into early Saturday.  The result will be HIGHLY dependent on the position of the cold air, the location of the cold front marking the leading edge to that chilly air (the front would serve as the pathway for the next storm) and, resultantly, the path of the next weak to moderate storm and therefore the track of its moisture.  If all were to come together, we'd be looking at some of the most southern reaching flakes of the season into Central and Southern New England, but as you've just read, there are quite a few factors still to watch.

Nonetheless, the pattern for the upcoming couple of weeks - the first half of December - will feature a fast flowing jet stream with numerous disturbances embedded in it, thanks largely to the weak El Nino flow and therefore the steady stream of disturbances racing across the Pacific and through the Western United States.  This will mean repeated tugs of cold air at the surface into New England, with plenty of availability to tap additional moisture from the tropical Pacific and Gulf of Mexico if any of these disturbances can grow strong enough, which they'll have a better chance of doing after the first week of December, when Pacific input strengthens even a bit more.

Enjoy your Monday!

Matt

Matt's Technical Meteorological Discussion:  Updated Monday, November 27 at 1:30 PM

30 degree spread across NewEng as of this writing from snow and 32 in Caribou, ME, to 62 and sun through Ci in OWD, SFZ, PVD, FIT.  Not bad for peak diurnal heating on what some would consider a quiet weather day!  Shortwave prompting rain and snow across Nrn ME will remain progressive, but so will the next shortwave upstream over Ontario as of this writing, which has been well-evidenced on radar and now shows good cloud top cooling on infrared imagery.  This shortwave will regenerate the swath of rain and snow across Nrn ME, and will a cooling boundary layer this should go to mostly snow with the I-95 corridor valleys starting as rain then changing to snow.  The shield of precip will drop south across Central ME and Bangor area may see a dusting by AM with temps around freezing which means black ice/icy spots a possibility, and accums of 2" possible higher terrain north of BGR area, esp from Millinocket points north.  Elsewhere, periods of clouds with shortwave passage seem rather innocuous but come prior to surge of shallow but meaningful cold that will migrate south behind Mon night's shortwave.  This cold has been brewing in Quebec and is a breakaway from gargantuan anticyclone in Central and Western Canada - therefore, this breakaway nature of the airmass means the cold is not overly deep but instead is a rather typical Eastern Canada surface dome that will be marked by a shift of winds to the northeast and brief gusts to over 20 mph with the wind shift.  Timing is 04-06Z in Portland and by 12Z most of NewEng has seen frontal passage.  Temps behind the front today are verifying in the 30s and NMM will verify best with this airmass thanks to its higher low level resolution.  Some areas in Srn NewEng will see falling temps after morning highs thanks to this cold advection.

Cold airmass remains locked in thru Tue Ngt, and areas of drizzle and light showers will be likely thanks to substantial low level instability.  Inversion present aloft, however, will strengthen Wednesday as warm advection commences above the boundary layer, but contrary to guidance forecasts I don't think the cold, dense air is going to give way to warm advection and mixing will be little if any, meaning low level deck remains locked in, isolated to scattered showers are possible thanks to warm advection aloft and temps remain cool.  Next system winds up enough to increase gradient and move air at the surface, so I do expect some warm advection in the boundary layer on Thu, though was looking at GFSX Ensemble members mostly in the middle 60s for Lawrence, MA, area Thu and I have a very hard time believing this with limited insolation and a stronger tendency for the cold to be rather begrudging in its departure.

In fact, as explained in the General Weather Summary above, I'd be surprised to find this cold air losing any meaningful battles in the next couple of weeks, and that includes Friday night, which is a critical battle in the world of meteorology, as nearly everything in the forecast will ride upon it.  I do mean quite literally "ride upon it" as the cold front will serve to be the path of the next incoming low.  I made my mind up which way to go with this for now when I reviewed the 00Z suite early today, and I have seen the warmer GFS solution even in its more recent 12Z run.  That said, I also see that the 00Z to 12Z has shown a rather substantial displacement to the southeast in the track of the low center - not yet where I'd expect it, but getting there.  So where would I expect the track?  Given the passage of a Thursday night shortwave similar to this coming night's wave, there's no reason to doubt whether the cold is capable of pushing thru NewEng.  It would appear as though the cruxt of the argument is the speed at which it sinks southward, to which we find good agreement among the Canadian Ensemble members and operational GGEM of a quick progression, GFS Ensemble mean position east and south of NewEng, and an ECMWF solution that is a bit more sluggish tho not nearly as sluggish as the GFS.  One could say that given the tendency for cold air to win the battles this time of the year, and the agreement among the Canadian Ensembles on the progression of this Canadian air - along with an NMM that also appears to be trending in a quicker cold direction, this certainly seems like the best forecast for the time-being.  Of course, in our discussions that's not quite enough, as I like to see synoptic reasoning to support guidance, and that synoptic reasoning is founded in the presence of confluent flow east of Maine, indicating the cold will come pouring in, then will hold.

Perhaps an equally challenging question is how the incoming Pacific vort will track and whether it will hold its identity as it encounters the confluent flow.  Thus far, the trend is only stronger with this Pacific energy as it lifts northeast across the OH/TN valleys, tho logic would say it should weaken as it approaches confluence.  I do think the guidance in general are still too far west with the vort max given the confluence east of NewEng and the colder surge as described above.  All of these factors raises my awareness of the potential for carrying accumulating snow farther south through New Eng than we've done so far this year, tho exactly where that is still remains up for grabs at 5 days out.  Heck, at 5 days out we know the whole thing remains up for grabs as described above, but of the solutions I prefer it would make the most sense to carry a moist Pacific-moisture loaded system either south of NewEng or over Southern NewEng Fri Ngt into early Sat, and this would mean the potential for accumulating snow even in Central NewEng.  It's also important to remember that shallow but strong cold can mean freezing precip, which wouldn't be impossible for interior locales if enuf cold air weren't present for snow.

So...plenty to work thru in the next couple of days.  In the meantime, enjoy the mild Monday (south) and the following chill Tuesday.

Matt