textproduct: Gray - Portland

SYNOPSIS

Scattered heavy snow showers and squalls along a cold front this afternoon will give way to gusty winds this evening and tonight. Temperatures will fall from the 30s into the single digits and even below zero in places by Friday morning. Wind chills even at the coast will be below zero. High pressure will arrive later Friday and more seasonable temperatures return Saturday.

NEAR TERM /THROUGH TONIGHT/

A cold front will continue to push through the region this afternoon with winds shifting to out of the northwest after it passes. Behind the front, most guidance suggests 3-hour surface pressure rises of 5 to 7 mb, along with strong cold air advection and steep low-level lapse rates. Forecast soundings suggest the potential for convective snow showers and some wind gusts up to 45 mph along and behind the front, especially across southern New Hampshire and portions of coastal Maine. A few heavy snow showers and/or squalls will be possible under the stronger reflectivity cores, so stay weather ready if traveling.

Attention then turns to the frigid temperatures expected tonight into Friday morning. High pressure will continue to push into the region overnight which should promote clearing skies. With the center of the high to our south, we could see some lingering clouds across the north but we should see enough clearing for some solid radiational cooling for most of the area, especially with a fresh snowpack in place. Lows will fall into the single digits below zero north, to the around 5 above zero south. A few readings in the double digits below are not our of the question in some of the northern valleys. Winds will be gradually diminishing overnight, but should remain fairly breezy. This will lead to widespread wind chills dipping into the double digits below zero, especially across the north where we could see values as low as 25 below. Some of the higher peaks could even see values of 30 below or lower and coastal regions should see wind chills below zero. We did expand the Cold Weather Advisory to include northern Grafton and southern Coos counties.

SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/

The center of the surface high moves off into the Atlantic by late Friday as the upper flow flattens and turns nearly zonal. Low amplitude ridging will then move across the forecast area on Friday night.

Frigid temperatures will be ongoing Friday morning as discussed in the near term. It will stay cold during the day but the winds will at least be much lighter. Highs will only range from the low to mid teens north, to the low to mid 20s south and along the coast.

Friday night shouldn't be as cold with some modest warm air advection forecast late. Lows will range from the single digits above zero north, to the lower teens south and along the coast.

LONG TERM /SATURDAY THROUGH THURSDAY/

Overview: The region will remain north of the primary storm track into this weekend as a strong jet positions over the Mid Atlantic. This keeps significant precipitation at bay for a couple days, but also keeps the area below normal for temperatures. A more stormy pattern emerges in the middle of next week.

Details: Exiting high pressure aids in some return flow Saturday. This brings some temperature moderation as well as moisture towards the coast. Guidance has been bringing some QPF to the coast through the day. This likely is aided by low level moisture arriving from the west via the tail of a passing front. This disturbance will also promote some mountain snow showers into Sunday morning.

Saturday night lows will feel mild compared to late week and early next, with values in the teens to around 20. These could end up a couple degrees cooler in spots that go calm, but a gentle breeze and some lingering clouds should prevent a full night of radiational cooling.

Northwest breeze continues Sunday as high pressure dives into the Midwest. This should weaken or end mtn snow showers as it advects drier air towards NH. Guidance has been depicting a weak disturbance ejecting out of the Great Lakes into New England for the evening and overnight hours. This comes in a few modes and strengths across the model suite, the GFS is the most amplified, while others depict a simple weak clipper. For now, a light dusting seems most likely from this system as it ushers back in colder temperatures. Overnight lows fall back into the single digits and teens.

Aforementioned Midwest high swings into the Northeast for the beginning of next week. This will return cold, below normal temperatures to the area Monday night. Lows again fall into the single digits above and below zero. Thankfully, with the high nearing overhead, it won't be accompanied by strong, gusty winds like present.

Exit of the high will bring an active pattern back to the region. Will be following an additional clipper system late Tuesday into Wed morning, and a potentially more potent system attempting to phase late Wed into Thursday. This would again have good jet dynamics to provide widespread lift ahead of a tilting trough aloft. A negative tilt may be achieved by the time the low pres moves into the Northeast, but questions remain if it remains progressive to the north or digs further east.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Short Term...An arctic cold front will move quickly through the region today, bringing a chance for heavy snow showers/squalls and brief local IFR or lower conditions. Behind the front, surface wind gusts up to 40 kts are possible this evening. Northwest of the mountains some lingering MVFR ceilings are possible in upslope flow/snow showers tonight.

Long Term...Some lowered ceilings to MVFR possible Saturday, with some light SN for coastal terminals. This lifts northeast in the evening, with SN continuing towards mountain terminals like HIE. Trend towards VFR Sunday and Monday.

MARINE

Short Term...A strong cold front is expected to push across the waters later this afternoon with strong wind gusts anticipated behind it. Gale warnings have been issued for all waters into tonight. While waters are still relatively warm, the coming air mass will be quite cold and some pockets of freezing spray are not out of the question.

Long Term...Conditions look to remain below SCA Saturday through Sunday. NW winds increase Sunday night into Monday as winds near 30 kt and wave heights build 4 to 5 ft. These briefly subside Tuesday before another system Wed into Thurs brings another period of greater winds and elevated seas.

CLIMATE

This air mass on Friday morning will be anomalously cold and low temperatures will approach records. This will especially be true at PWM where the forecast is 2 degrees and the current record is 7 in both 1989 and 1945. The forecast at AUG is 2 degrees and the current record is 4 set in both 1989 and 1991.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Cold Weather Advisory from 9 PM this evening to 8 AM EST Friday for MEZ007>009. NH...Cold Weather Advisory from 9 PM this evening to 8 AM EST Friday for NHZ001>003. MARINE...Gale Warning until 5 AM EST Friday for ANZ150-152-154. Gale Warning until 3 AM EST Friday for ANZ151-153.