Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
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548 FXUS61 KGYX 251057 AFDGYX Area Forecast Discussion National Weather Service Gray ME 657 AM EDT Wed Sep 25 2024 .SYNOPSIS... High pressure retreats northward as moisture works its way into the region today and tonight. Low pressure keeps north as a triple point of fronts moves through the area Thursday. This brings much needed rainfall to the area, albeit heavy at times. Dry weather returns in time for the weekend as high pressure moves overhead. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 7am Update...Expanded rain chances in western NH this morning. Showers have been drifting through NY and VT overnight, and look to clip NH for a couple hours. Precip is expected to be light, but will create some damp spots through noon. Otherwise, a few passing sprinkles continue in southern NH and ME. Previous Discussion... Cloudy and cooler today ahead of wetting rainfall tonight through Thursday. Onshore flow will continue today, bringing with it moist low level air. This will be responsible for a lower deck of cloud for much of the coast and interior today, with some breaks in the mountains and towards the Quebec border. Can`t rule out a sprinkle here and there as upper moisture also passes through the region from the SW. Should dry layer thin enough in places through the morning hours, could see brief seeder/feeder showers. With the clouds in place, went a little lower than guidance today for highs. Highs in the mid to lower 60s are forecast for much of the area. This may only be exceeded by southern NH locations which have instead been insulated by the overnight cloud, missing a window of radiational cooling in the Tues evening hours. Along the coast, there remains waves of 5 to 6 ft at long periods that can bring moderate to high surf and rip currents. Will continue to assess the needs for any coastal products, but current thinking is more overcast today will lead to less crowded beaches. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Mild tonight as cloud cover from the daytime sticks around. The area will also see increasing WAA through much of Thursday as return flow strengthens ahead of incoming low pres from the north. Tonight, shower chances increase west to east as low pres advances. There is uncertainty on exact start time of steadier rain, but it should be falling come Thursday morning for much of the interior and northern NH. The day shift already pointed out some good parameters to watch for this much needed batch of rain including a favorable PWAT range and warm cloud depth of around 12 kft. With some elevated instability present, I added mention of thunder in the afternoon across southern NH and ME. This comes into play around when upper level 140kt jet flattens with good net lift across the CWA. Some longer time frame CAMs are picking up on the likelihood of heavy rain, Thursday afternoon. HRRR and NAMnest are trying to even resolve a fine line of convection developing in the region. Strong winds with this line are currently not forecast, but can`t rule out some additional gusts amid a quick wind shift as this passes. The biggest impact may be very heavy rainfall as it passes, reducing visibility and contributing to the risk of hydroplaning around the afternoon commute. The threat of flash flooding remains low due to the very dry antecedent conditions, as well as progressive nature of this system tonight through Thursday. That said, some enhanced rainfall rates could lead to nuisance ponding of water around low spots as well as if any storm drains have collected the first fallen leaves of the season. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Overview: The period will start wet as a 500mb trough dives into the region and moves overhead Friday. It exits by Friday night followed by height rises through the weekend. The ridge axis looks to be centered on us Monday, before another trough approaches Tuesday along with another chance for showers. Impacts: * No significant weather impacts expected. Details: Showers exit the area shortly after sunset and skies begin to clear overnight, but gradual enough that low temperatures likely only bottom out in the 50s. There will be just enough moisture wrapping around the low on Friday to squeeze out a couple light showers, mainly in and around the mountains, as the upper low slowly exits through the day. Otherwise, high pressure begins nosing in from the north so mostly clear skies will allow temperatures to warm into the upper 60s and low 70s from the foothills south, and in the mountains and points north, northerly flow and a tad more cloud cover will keep temperatures in the low 60s. Low temperatures Friday night will be a bit cooler than Thursday night, but lingering clouds will keep them very similar. High pressure takes full control for the weekend with Saturday and Sunday featuring mostly clear skies, calm winds, high temperatures in the 60s, and low temperatures in the upper 40s. High pressure looks to hang on for Monday before the pattern becomes a little more uncertain due to the fact that Tropical Cyclone Helene will be moving inland in the southern U.S. This will have an effect on the timing of the next trough, as differences in global models currently show, so will stick with the NBM low chance PoPs on Tuesday for now. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Short Term...MVFR today for most terminals, with periods of IFR. A trend towards VFR is possible for RKD/AUG this afternoon, but the trend returns to MVFR/IFR restrictions after midnight into Thursday. SHRA works into the region overnight, becoming RA for Thursday. Some TS possible in the afternoon for mostly southern terminals. RA may be heavy at times, causing additional vis restriction. Long Term...Thursday will likely feature a mix of MVFR and VFR ceilings as rain, locally heavy,moves through the area. Friday morning may feature some fog but afterward VFR should be the prevailing condition right through the weekend. Winds will be light with gusts generally 10-15kts. && .MARINE... Short Term...Wave heights 4 to 6 ft continue through Thursday, mainly for the waters south of Penobscot Bay. Have extended the SCA through to Thursday evening. This may need extension northward for tomorrow. Wave heights and periods continue to align for possible high surf at times. Either way, those recreating along the beaches should be aware of moderate rip current risk, potentially extending through late week. Long Term...Max wave heights of 5ft remain through at least Friday morning before finally dropping below 5ft later in the day and remaining below SCA criteria through the weekend. Winds will be gusting 15-20 kts on Thursday and Friday before high pressure begins to move over the waters and calm them a bit for the weekend. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until 8 PM EDT Thursday for ANZ152>154. && $$ NEAR TERM...Cornwell SHORT TERM...Cornwell LONG TERM...Baron