REPEATED TUGS OF COLD AIR TO BRING PERIODS OF GRAY...BUT COULD GRAY + COLD = WHITE GROUND BY FRIDAY NIGHT?
POTENTIALLY PARALYZING STORM FOR SOME CENTRAL U.S. CITIES TO HEAD INTO NEW ENGLAND ON FRIDAY

AS COOL AIR ESCAPES FROM CANADA, STUBBORN GRAY SKIES FOR MOST

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:

A surge of cold air has been sagging southward through New England on Tuesday and will bring a winter chill to some spots Tuesday afternoon, only begrudgingly letting go as the week progresses and milder, more moist air makes a run back at New England.

The passage of an upper level disturbance Monday night across the Canadian border brought minor snow accumulations to the higher terrain of Central and Northern Maine, where some slick road conditions began Tuesday morning.  But this disturbance also provided a southward tug of cold air that's been welled up across Quebec, marked by a shift in the winds to blow from the northeast.  This wind shift - a cold front - has continued settling south of New England on Tuesday, opening the gates for that cool air to seep southward from its Eastern Canadian well, knocking temperatures down through the day in some areas and bringing coastal gusts of wind in excess of 20 mph.  By the end of Tuesday, under gray skies with drizzle and mist for most Central and Eastern New England areas, and fog through parts of Vermont and Western Massachusetts on the edge of the deeper cool air, most communities will average around 40 degrees with a very raw feel. 

Those raw conditions will continue Tuesday night into Wednesday, even though warmer air will be moving back in thousands of feet above our heads.  Given the density of this heavy, cold air, that return of warmth will barely make it to ground level through the day on Wednesday, and instead will simply set up a continued clash between two airmasses, meaning continued 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.  The important question with this forecast was discussed here yesterday, and revolves around the timing of an incoming cold front, poised to drop out of Canada as the aforementioned storm charges across New England.  Though I'm willing to bring warm air into New England on Thursday as the cold dome erodes and winds increase from the south, there are two major reasons the pattern favors pulling cold air back 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 moderate strength 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 through Friday night.  The result of this disturbance 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.  At this point, the most likely scenario is to swing rain through most of New England on Friday, though Northern Vermont, Northern New Hampshire and Central/Northern Maine will be close enough to the significant cold air of Canada to warrant keeping a close eye on what may be an accumulating snow, especially Friday.  Farther south through the remainder of New England, it's possible that as the precipitation ends late Friday into Friday night, enough cold air moves in to end as some snow showers, though this is something that bears continued watching as it's far from set in stone.

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.

Have a great Tuesday!

Technical Discussion:  After a lengthy techie discussion yesterday (posted below), will use today to tend to busy behind-the-scenes day.

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