Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
853 FXUS61 KGYX 181834 AFDGYX Area Forecast Discussion National Weather Service Gray ME 234 PM EDT Fri Sep 18 2026 .WHAT HAS CHANGED... No major changes were needed for this forecast package. && .KEY MESSAGES... 1. High pressure moves in for tonight and Saturday with fair weather. Areas of of frost possible across mountain valleys in the north tonight. 2. Low pressure will bring a period of rain Sunday into Sunday night. 3. High pressure brings mostly fair weather Monday through Wednesday with temperatures running below normal. && .DISCUSSION... KEY MESSAGE 1 DESCRIPTION... While high pressure will start to settle into the region tonight, the center will be only be near the Ontario/Quebec border by early Saturday morning. Thus the pressure gradient may not relax quite a bit as it appeared in previous days. Therefore, northwest winds may remain on the breezier side through the night which may help to keep temperatures from plummeting. Some high clouds may also be floating around. Still, it appears that we will see some lows in the mid to upper 30s across the northern mountains which could lead to some areas of frost. Lows will mainly be in the low to mid 40s elsewhere. The most favorable area for frost appears to be over the far northern valleys where we will likely see winds taper off sooner. Have held off on any Frost Advisory for now given the uncertainty regarding winds and cloud cover. The core of the high will move into New England on Saturday which will mean fair weather with high temperatures mainly in the 60s, plenty of sunshine, and light/variable winds. Lows on Saturday night should be similar to tonight but maybe just a touch warmer with clouds forecast to be on the increase through the night. KEY MESSAGE 2 DESCRIPTION... Convection that has yet to blossom over the central Plains is modeled to produce a mid level short wave that will track west to east across the Northeast late Sunday. As is often the case with convectively induced short waves, there is a spread amongst model guidance in the trajectory and strength of the wave which has implications for PoPs and QPF amounts. There will be additional support for lift Sunday into Sunday night as the right entrance region of an upper jet slides over northern New England. Models generally agree that this wave will produce a surface low tracking near the area to bring some beneficial rainfall centered on Sunday afternoon. The latest NBM brings at least chances PoPs across the entire area with precip chances 60-80 percent across NH into SW Maine by Sunday afternoon. Total QPF will range from 0.75 inches across SW NH to around a tenth of an inch across central Somerset County. Although some ensemble members and the RRFS leave the forecast area mostly dry, I am not inclined to deviate from the NBM based on the suite of guidance. PoPs will decrease from NW to SE as the surface low exits and high pressure builds in from the NW. KEY MESSAGE 3 DESCRIPTION... Deterministic and ensemble guidance are in good agreement that broad high pressure will drift from southern Canada across northern New England Monday through Wednesday. This will promote fair weather with temperatures running below normal. There is a signal for a coastal low to develop near the Mid Atlantic during this time range that could throw some clouds into the area and hamper radiational cooling. If skies remain clear at night than temperatures will likely drop low enough for frost formation across interior valleys. Models suggest the coastal low will slowly drift northward the second half of next week with precip chances arriving around Thursday. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... VFR conditions are expected for the rest of today with NW wind gusts of 20 to 25 kt at times. VFR tonight but there could be some valley fog over the CT River Valley if winds can diminish quickly enough. Will not include mention at LEB yet due to this uncertainty. VFR with lighter winds on Saturday with high pressure overhead. Outlook... Sunday-Sunday night: Low cigs and rain likely bring MVFR with periods of IFR along and south a line from LEB to PWM. Monday-Wednesday: Mainly VFR, outside of overnight valley fog. && .MARINE... Behind a cold front today, wind gusts around 20 kt are likely, with a few to around 25 kt. Breezy conditions may linger through tonight with tranquil weather settling on Saturday as high pressure moves overhead. Winds and seas likely remain below SCA thresholds Sunday into Monday while a wave of low pressure passes south of the waters. This low will bring periods of rain and potential for fog. A NE gradient will develop late Monday through mid week as high pressure builds in from the north and a coastal low develops near the Mid Atlantic. NE winds could gust around 25 kts at times with seas building 5-6 feet by late Wednesday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ DISCUSSION...Hargrove/Schroeter