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
