textproduct: Gray - Portland

SYNOPSIS

The first widespread winter storm is expected to bring a plowable snow to much of the region today into tonight. The weather will briefly turn quieter on Wednesday before an Arctic cold front brings snow squalls and breezy conditions Thursday afternoon and evening before temperatures turn sharply colder to end the week. Additional snow shower activity is possible again this weekend as a series of disturbances cross the region.

NEAR TERM /TODAY THROUGH TONIGHT/

Key Messages:

Winter Storm Warnings and Advisories remain in effect this morning into tonight. Cold temperatures this morning will prime roads for accumulating snow this morning. Snow breaks out between 8 and 10 AM and will become heavy at times this afternoon through the evening commute creating hazardous travel.

A corridor of heavy wet snow is likely just inland from coast into southern New Hampshire that will cling to branches bringing a limited power outage threat.

Forecast Details:

No significant changes in the overall forecast thinking as a progressive area of low pressure tracks southeast of Cape Cod this evening spreading snow into the region today. The low exits east tonight with snow tapering off NW to SE during the pre dawn hours Wednesday morning. Favorable dynamics with the right entrance region of an upper jet streak sliding over northern Maine will aid in the development of a moderate to heavy snow band/s northwest of the low center. The latest WPC Snowband Probability Tracker (SPT) has become more bullish over the past couple of runs with the potential for SW to NE bands developing over south-central NH this afternoon and slowly translating ENE across Maine through this evening. The latest hi res guidance suggest that snowfall rates of 1+ inch per hour will be possible within these bands. The WPC SPT does suggest that areas from the southern Whites to the coast could have this band/s move overhead bringing the potential for hazardous travel with visibility reduced to one quarter a mile.

The latest NBM has come in wetter and warmer near the coast, as at this time range it places higher weight on CAMs. This brings the rain snow line several miles inland and may push west of I-95 at times across SW Maine and SE NH. Have utilized the 925 0C isotherm as proxy to lower temperatures as heavy precipitation rates can increase evaporative cooling and overcome marginal surface temperatures for accumulation. After lowering temperatures within areas of heavier rates, the latest snowfall forecast has come down across southeast NH and coastal Maine. While snowfall amounts come short of Warning criteria, have left the Warnings here unchanged because the timing of a couple hours of heavy snow during the evening commute will still bring dangerous travel conditions. The slight increase in QPF did bump up snow totals across the interior while overall the forecast calls for 6 to 10 inches within the Warning and 3 to 6 inches north of the mountains. There will likely be a sharp gradient in snow amounts within a few miles of the coast.

As the low pulls east tonight winds shift northerly allowing any rain near the coast to change back to snow. Snow will taper off after midnight from NW to SE with snow likely ending before the Wednesday morning commute. Coastal areas could see a few inches of snow after the change over tonight. Northerly winds will increase this evening and will remain gusty overnight with peak gusts 25 to 30 mph.

SHORT TERM /WEDNESDAY/

High pressure noses in from the SW Wednesday allowing gusty winds to diminish. Mostly sunny skies will turn partly to mostly cloudy late in the day as a front approaches from SE Canada. Highs on Wednesday will range from the 20s north to upper 30s south.

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/

Overview: An Arctic front will cross on Thursday afternoon, bringing the potential for snow squalls. Bitterly cold windchills are then expected Thursday night behind this front. There remains uncertainty about another potential winter storm this weekend but it bears watching. Temperatures will mainly remain below normal through the long term period of the forecast.

Impacts: Snow squalls are possible on Thursday afternoon and evening as an Arctic front crosses the region. These will have the potential to produce rapidly deteriorating travel conditions. In addition, NW wind gusts up to around 35 mph are possible. Sub- zero windchills are expected Thursday night.

Forecast Details: A positively tiled H5 trof axis over Hudson Bay will continue to move east towards New England on Wednesday night ahead of an Arctic front that will cross on Thursday afternoon. Wednesday night will feature mainly cloudy skies with snow showers developing across the mountains and towards the Canadian Border after midnight. Low temperatures will be into the teens to lower 20s. The aforementioned Arctic front will cross Thursday afternoon/evening as the H5 trof crosses the area while becoming negatively tilted. T8s will drop to below -20C, which combined with some instability from sfc heating will allow for potential snow squalls during the afternoon and early evening. Any squalls will have the potential to result in rapidly deteriorating road conditions. In addition, the increasing low-lvl jet will allow for NW wind gusts up to around 30- 35 mph along and behind the front. High temperatures will be relatively mild into the lower 30s across the north to around 40 degrees along the coast and in southern NH.

Bitterly cold windchills are then expected Thursday night with widespread below zero values. Actual forecasts lows range from around -5 across the north with single digits elsewhere. It is possible that some northern zones could approach cold weather advisory criteria. Blustery conditions will persist on Friday with windchills remaining into the single digits and teens under partly cloudy skies. Friday night will remain cold with lows into the single digits and lower teens. Forecast uncertainty then increases this weekend as some guidance shows another potential coastal low near New England while other guidance keeps this suppressed to our south. It bears watching as we get closer to see how things trend but temperatures would likely be colder enough for snow in most locations should the precipitation reach the area. Another Arctic front is likely to cross Sunday night with another push of well below normal temperatures for early next week.

AVIATION /05Z TUESDAY THROUGH SATURDAY/

Short Term...VFR will prevail into day break. Snow breaks out after 12Z with IFR to LIFR likely from late morning through 06Z tonight. Conditions improve to VFR Wednesday. NE to N winds will gust around 20 to 25 kts this evening through tonight.

Long Term...Mainly VFR conditions are expected through the period. Scattered heavy snow showers or squalls are possible on Thursday afternoon and early evening as an Arctic front crosses, and these could bring brief periods of IFR-LIFR restrictions. In addition, NW wind gusts behind the front could approach 30 kts Thursday afternoon and evening. More persistent MVFR CIGS are likely at KHIE behind this front through Thursday night due to developing upslope flow.

MARINE

Short Term...Low pressure tracks near Cape Cod this evening and towards Nova Scotia tonight. Temperatures will be warm enough for mainly rain over the waters. NE to N winds increase this evening with Gales likely tonight into Wednesday morning along the outer waters.

Long Term...Northwesterly gales are possible Thursday afternoon through Thursday night behind an Arctic front with seas outside of the bays building to 4-6 ft. Light freezing spray is possible as very cold air moves across the waters. Winds and seas then look to remain below SCA levels through Sunday.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Winter Weather Advisory from 8 AM this morning to 4 AM EST Wednesday for MEZ007>009. Winter Storm Warning from 8 AM this morning to 4 AM EST Wednesday for MEZ012>014-018>028-033. NH...Winter Weather Advisory from 8 AM this morning to 4 AM EST Wednesday for NHZ001>003. Winter Storm Warning from 8 AM this morning to 4 AM EST Wednesday for NHZ004>015. MARINE...Gale Warning from 10 PM this evening to 10 AM EST Wednesday for ANZ150-152-154. Small Craft Advisory from 10 PM this evening to 10 AM EST Wednesday for ANZ151-153.