textproduct: Gray - Portland

SYNOPSIS

Low pressure approaches from the west today spreading accumulating snow across the interior through tonight while coastal areas see mainly rain. A cold front crosses Thursday morning with a prolonged period of gusty winds in its wake through Friday. High pressure briefly builds in Friday night into Saturday before the next trough approaches from the Great Lakes.

NEAR TERM /THROUGH WEDNESDAY/

Passage of the first front right now is fighting some dry air at least initially. That has resulted in mostly very light snow/snow showers with visibility generally greater than 2SM. As expected though the radar returns are getting more robust over the Midcoast and that is expected to continue for the next several hours. It is from these areas and points east where an inch or two remains possible.

However the more widespread precip will arrive with the next front later today. I anticipate the bulk of the precip arrives around or after noon. Trends on temps have been cooler...but not quite cool enough over southern NH and near the coast to save those areas from flipping to rain for a time. With the air mass remaining rather cold I could see most areas starting as snow...but that is unlikely to hold at least mid level warmth at bay. Hi-res guidance is now showing 2 m temps to remain cold across the forecast area...for instance PWM struggling to make 32 degrees today. However that may just bring a wintry mix instead. 925 mb temps will still climb above freezing for a good chunk of the area south of the mtns...and so a transition period of light freezing rain is a possibility. An expansion of winter weather advisories may be necessary if trends continue. Otherwise there has been little change to the forecast from previous shifts. For parts of the Kennebec River Valley where colder air is expected to hang on longer I have expanded the winter weather advisory for one such period of freezing rain.

SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/

Whatever precip is left will come to an end...especially after midnight. After that we transition to northwest winds and upslope snow showers. Generally left PoP as is from the NBM with active short term weather of concern...but I could see the need for those values to bump up in subsequent forecast updates. Flow will also be largely unblocked and snow showers should easily crest the mtns and spill towards the coast. NBM PoP generally has pretty good coverage on that front.

One spot it does not seem to be handling well is the cold advection mixing. Forecast soundings across the forecast area have mixing heights high enough to tap 40+ kt winds. That should easily bring 30 to 35 kt gusts to the surface over the latter half of Thu when the CAA is the strongest. I have blended in some 90th percentile NBM winds and hi-res guidance to compensate for this.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

A mid level low will deepen as it tracks across northern Maine Thursday night and Friday. Deep layer westerly flow will strengthen on the backside of this system resulting in blustery conditions Thursday night through Friday as a colder airmass advects into the region. Winds subside Friday night into Saturday as high pressure briefly builds in from the southwest. The next northern stream trough approaches Saturday into Sunday bringing chances for light snow.

A WNW low level jet will strengthen over northern New England Thursday night into Friday as low pressure becomes vertically stacked over the Canadian Maritimes. Winds at 850 mb will approach 60 kts while BUFKIT profiles suggest that the top of the mixed layer will come short of tapping into these winds. Nevertheless, mean layer momentum transfer of 35 kts will bring potential for wind gusts up to 40 mph Thursday night through Friday with much stronger winds in the mountains. These winds combined with a colder airmass will result in wind chills below zero across much of the area Friday morning. Skies turn mostly sunny south of the mountains by Friday afternoon with highs ranging from the teens north to upper 20s south.

High pressure briefly builds in Friday night into Saturday morning allowing winds to subside. A short wave will shear out as it approaches Saturday afternoon while vort max diving southeast across the Dakotas deepens a long wave trough centered over the Great Lakes. A few ensemble members and the occasional deterministic run have shown this vort max spawning an organized low pressure system crossing New England Sunday. Were these solutions to verify then we would see potential for widespread accumulating snow. However, these solutions are in a minority with NBM PoPs running 20 to 30 percent late Saturday night through Sunday.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

Short Term...Generally VFR this morning withe TEMPO MVFR or IFR conditions in snow as it moves in pockets thru the forecast area. This will mostly move out of the area by 08z at the latest. Then the next batch of precip moves in around midday. This will bring IFR or lower conditions to the northern half of the forecast area at least...where snow is the predominant ptype. This may end up pushing closer to the coast if colder trends continue. While winds aloft will be quite strong both this morning and again later today...they will be largely unidirectional. So LLWS is not anticipated but low level turbulence is likely. Then winds turn westerly and VFR returns. Surface gusts to 30 kt are possible at all terminals except HIE by afternoon.

Long Term...Mainly VFR Thursday night through Sunday. WNW winds will gust to 30 kts Thursday night through Friday. There are low chances for light snow Saturday night into Sunday that will bring the potential for the next period of restrictions.

MARINE

Short Term...Gusty winds continue this morning and will be followed by stronger winds later today. Gale warning and SCAs continue over the coastal waters. After the cold front drives thru the region Thu strong westerly winds are anticipated. Another round of gales is likely...and they may be strong gales.

Long Term...West winds will bring potential for Gales Thursday night through Friday. Winds and seas drop below SCA thresholds Friday night into Saturday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 7 AM Wednesday to 1 AM EST Thursday for MEZ007>009-012>014. NH...Winter Weather Advisory from 7 AM Wednesday to 1 AM EST Thursday for NHZ001>004. MARINE...Gale Warning from 1 PM Wednesday to 1 AM EST Thursday for ANZ150-152-154. Small Craft Advisory from 1 PM Wednesday to 1 AM EST Thursday for ANZ151-153.