Area Forecast Discussion
Issued by NWS Caribou, ME

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000 FXUS61 KCAR 211430 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 1030 AM EDT Thu Sep 21 2023 .SYNOPSIS... High pressure will build in from the west today, cross the area tonight, then slide south of the region Friday into Saturday. Low pressure will track to our south on Sunday into Monday. High pressure slowly builds eastward into the area Tuesday into Wednesday. && .NEAR TERM /THROUGH TONIGHT/...
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Update... Surface high pressure will build east toward the region today, while upper level troffing moves across the Maritimes. With diurnal cloud development, expect mostly/partly sunny skies across northern and central areas today with mostly sunny skies Downeast. High temperatures will range from the lower to mid 60s north, to the upper 60s to around 70 Downeast. Have updated to adjust for current conditions along with expected afternoon temperatures and clouds. Previous Discussion... Tonight, a 1029mb surface high slides right overhead as the 500mb ridge axis slides into Quebec. This ends the cyclonic flow over Maine and conditions become very light. Light winds, clear skies and high pressure means a very good radiational cooling night expected. One caveat may be the extremely soaked grounds in Maine since soil moisture in the root zone is in the 95-99th percentile for this time of the year. However, felt confident in lowering the colder valleys a degree or two using the NBM 10th percentile. This will result in lows Friday AM in the low to mid 30s across the North Woods with patchy to areas of frost. The frost/freeze program is ending today in these zones and given how basically it isn`t expected to be widespread opted to not hoist any headlines. Across the rest of the crown expecting lows around 40F but some upper 30s are possible in the colder deeper valleys and its here there may be some patchy frost but confidence is lower so no headlines at this time. Elsewhere, from the Baxter Region south to the Downeast coast expecting lows 40-45F with a few upper 40s at the shoreline. Lastly, expecting patchy fog to develop in the river valleys and over the ponds/lakes tonight with colder air, moist grounds and warmer bodies of water. This may reduce visibility for the morning commute in locations on Friday AM.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... A 1030mb high will be parked over the area Friday morning and slowly drift offshore by Friday afternoon into Friday night. With little to no cloud cover and light winds, H925/H850 temps suggest afternoon temps reaching the upper 60s to around 70F. An emerging onshore flow will limit highs on the coast to the upper 50s to lower 60s. For Friday night, light winds and generally clear skies will produce another night of decent radiational cooling with a shallow inversion yielding lows in the low to mid 40s. Once again, fog will be likely in valleys over relatively warmer rivers and lakes. After the high retreats to the east, the big question for the weekend will be the northward transport of deep tropical moisture advecting from a closed low along the North Carolina coast. An omega block will be trying to set up towards the end of the period. The forecast area will end up on the east side of the block. Some guidance, most notably the GEMS, brings the deeper moisture northward into the forecast area Saturday night...albeit not as far north as previous runs. Meanwhile, GFS and ECMWF continue to swing a northern stream shortwave and cold front southward Saturday night that shunts the moisture off to the east before getting much further north than the Downeast coast. Have followed this latter scenario in the forecast in line with NBM guidance. ECMWF trended more northward with precip on Saturday night with the 21/00Z run and looks more reasonable than the last few GFS runs. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Blocking continues through the period. Again, the evolution of the tropical moisture on the east side of the omega block looms large into early next week. GEMS continues to be the most pessimistic with the cut-off low migrating from the Carolinas to Maine Sunday into Sunday night while ECMWF and GFS push a reinforcing northern steam trough southward out of Quebec Sunday into Monday. This is a considerably drier solution and following NBM, we maintained relatively low PoPs into early next week. That said, confidence is not particularly high in a dry start to next week across the forecast area and do not give much credence to the GFS solution. The likelihood of drier weather increases by mid-week as the expansive surface high associated with the block slowly expands eastward. Temperatures and cloud cover will be tricky as this occurs due to the prospect of stratocu in the a northerly or northeasterly flow in a subsidence inversion. Thus we stuck towards the NBM and near normal temps towards the end of the forecast period. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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NEAR TERM: Occasional MVFR ceilings possible across northern and central areas this morning. Otherwise, VFR today through early tonight. Variable conditions possible late tonight with any patchy fog. North/northwest winds 10 to 15 knots with gusts up to around 20 knots today. Light and variable winds tonight. SHORT TERM: Friday...Patchy valley fog is possible early for sites such as PQI, but otherwise VFR. Light south winds. Friday night...Patchy valley fog again in river valleys will possibly affect sites such as PQI and HUL after midnight. Light winds. Saturday...Patchy valley fog is possible early for sites such as PQI, but otherwise VFR. SW winds 5 to 15 kt. Saturday night and Sunday...VFR from GNR, MLT and HUL northward. Chance of MVFR cigs/vis in rain for BGR and BHB. Light north winds. Sunday night and Monday...VFR with a slgt chc of MVFR cigs. Light north to northeast winds.
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&& .MARINE...
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NEAR TERM: Winds/seas below small craft advisory levels today through tonight. SE long period swells from Hurricane Nigel which is located 550mi SSE of Cape Race, Newfoundland will be occurring across the Gulf of Maine today into tonight. Wave periods 14-15sec today becoming 12-13sec tonight. Waves are expected to generally be 2-4ft but cannot rule out a few waves to 5ft across the waters 20-25nm offshore. Waves will subside to 1-3ft tonight. SHORT TERM: No fog is expected through the period. There are no clear cut SCAs lurking into the middle of next week either. Northeast winds will increase Sunday, but gusts should stay under 20 kt as it looks now. Northerly wind gusts will likely exceed 20 kt on Tuesday, but confidence is not high in 25 kt gusts at this time.
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&& .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...None. && $$ Near Term...Norcross/Sinko Short Term...MCW Long Term...MCW Aviation...Norcross/MCW Marine...Norcross/Sinko/MCW

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