textproduct: Gray - Portland

WHAT HAS CHANGED

No notable changes to the forecast this evening.

The Cold Weather Advisory for tonight has been expanded to include southern Oxford county, Cumberland county, coastal York county, and coastal Rockingham county.

No significant trends in the coastal low with a close approach to Southern New England with periphery minor coastal impacts still in the cards.

KEY MESSAGES

1. Remaining very cold through Saturday night with winds chills in the double digits below zero possible each night. Winds chills will likely remain below zero in many areas during the day Friday.

2. A strong coastal low may bring impacts to the coast on Sunday, but most guidance favors a track far enough offshore to keep the impacts minimal.

3. Marine weather impacts are expected Sunday into Monday as the close approaching coastal low brings Gale/Storm force winds.

4. High Astronomical Tides Sunday through Monday and the close approaching coastal low provide a threat for minor coastal flooding late this weekend into Monday.

DISCUSSION

KEY MESSAGE 1 DESCRIPTION... Another frontal boundary/trough moves through this afternoon and evening, bringing with it a chance of snow showers in the mountains and possibly a few flakes downstream as Froude numbers depict unblocked flow. Otherwise it will just further reinforce the already cold airmass as W/WNW become somewhat breezy and CAA increases through tonight and Friday.

Overnight temperatures are expected to fall below zero for the majority of western ME and NH again tonight, and we should stay mixed enough to maintain a breeze to push wind chills in the double digits below zero in most places. However, even if winds are able to drop in some places, it will be very cold regardless as mostly clear skies should promote radiational cooling, although some clouds or even a few snow showers may move in from the north overnight as a 500mb shortwave dives south. Cold Weather Advisories are in effect across the mountains and foothills for wind chills in the -20 to -25F range tonight and closer to -15 to -20F for the southern half of NH and into southwest ME. For those outside the advisory area, wind chills could still approach the -10 to -15F range.

CAA continues on Friday with temperatures expected to be limited to the teens south of the mountains and in the single digits to the north. To make it feel even colder, good mixing will result in wind gusts of 20-25 mph, which will likely keep wind chills below zero during the day south of the mountains, or at best a few degrees above. In the mountains, wind chills may stay in the double digits below.

The pressure gradient relaxes and brings lighter winds for Friday night, but that trade off is good radiational cooling with mostly clear skies. With this in mind, I have trended the already cold NBM (which had lows below zero) more toward the MAV for overnight lows.

Dry conditions are expected Saturday, and even though temperatures may only reach 20 degrees south of the mountains, it won't feel as cold with lighter winds. Saturday night will again be very cold with subzero temperatures away from the coast. For southern NH and the coast, temps may stay above zero due to some clouds moving in from the coastal storm to the south and/or more of a breeze.

KEY MESSAGE 2 DESCRIPTION... A very strong low pressure system looks to move northeastward over the Atlantic on Sunday. Ensemble guidance has shown a stronger signal for the center of the low to move east of the benchmark (40N, 70W). The more easterly track should keep most heavy accumulating snow offshore. However, at least 2-5 inches of snow still appears possible along the coast and could skew visibility significantly as snow should get blown around with breezy conditions.

KEY MESSAGE 3 DESCRIPTION... Perhaps the most impactful weather associated with the upcoming storm is not necessarily the snowfall but the high winds over the Gulf of Maine. There look to be at least gale force winds over the area with potentially some storm force gusts as well. The threat should mainly stay offshore. For more details, please see the Marine section.

KEY MESSAGE 4 DESCRIPTION... Will have to monitor for coastal flooding as we are entering a period of high astronomical tides. The strong N/NNE winds will create high seas and storm surge, which may allow for some areas to reach minor flood stage at high tide on Sunday. The potential is still there on Monday, but with winds becoming more northwesterly, the threat appears lower.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Through 18Z Friday...Primarily VFR other than periods of MVFR ceilings and a chance of snow showers at HIE.

Outlook:

Friday afternoon - Saturday night: Continued chance of MVFR at HIE, but otherwise VFR prevails.

SUNDAY / MONDAY...Coastal low moves into the area, allowing for substantial CIG and visibility restrictions along the coast. Less impactful restrictions more likely at inland sites.

TUESDAY...VFR Expected.

MARINE

W-WNW winds gusting to around 30 kt tonight and 25 kt Friday will maintain SCA conditions over the outer waters and Penobscot Bay through Friday along with freezing spray. Winds and seas then come down below SCA levels Friday night and Saturday as the pressure gradient relaxes. Northeast winds increase late Saturday night as deepening low pressure approaches from the south.

A storm moves across the Gulf of Maine Sunday through Monday. Seas start off at 2-6ft Sunday morning and quickly escalate to 7-15ft over the open waters, with 4-7ft expected in the Bays by Monday morning. In addition, winds start off Sunday morning as Gale force, strengthening to Storm force by the end of the day. Storm force winds continue Sunday night and recede back to gale force by Monday morning. Gales are expected Monday, but should weaken to SCA levels by the end of the day as the aforementioned low exits the region. Winds may calm even further on Tuesday. Seas lower on Monday as well, coming down to 3-5ft by Tuesday morning.

GYX WATCHES/WARNINGS/ADVISORIES

ME...Cold Weather Advisory from midnight tonight to 10 AM EST Friday for MEZ007>009-012-018-019-023-024-033. NH...Cold Weather Advisory from midnight tonight to 10 AM EST Friday for NHZ001>015. MARINE...Small Craft Advisory until 7 PM EST Friday for ANZ150-152-154. Freezing Spray Advisory until 7 PM EST Friday for ANZ150>152- 154. Small Craft Advisory until 1 PM EST Friday for ANZ151. Freezing Spray Advisory until 1 PM EST Friday for ANZ153.