Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 131923 AFDGYX Area Forecast Discussion National Weather Service Gray ME 323 PM EDT Sun Oct 13 2019 .SYNOPSIS... Low clouds and patchy fog will increase again tonight, lasting into Monday, mainly on the coastal plain and inland Mid Coast. A vigorous low pressure system is likely to move across the forecast area starting Wednesday, and may allow for a period of heavy rain and windy conditions Wednesday night into Thursday. High pressure will slowly build over the region from the west Friday and into the weekend. && .NEAR TERM /THROUGH TONIGHT/... Mid-level ridging provides a nice day locally with temperatures climbing a couple degrees above average and some Mid Coast cloud cover. Meanwhile further west, a strongly forced closed low churns over the Great Lakes region and central Ontario. Tonight, heights aloft begin to fall as a shortwave axis rotates around the closed low toward New England. Hires guidance including the HREF continues to suggest onshore low-level flow/weak positive moisture advection developing overnight with high pressure moving offshore. This will likely lead to a blanket of low stratus and fog by Monday morning along coastal NH and ME, further into the coastal plain in ME with greater southerly component to flow. Temperatures are a bit tricky tonight; decoupling is likely early on, leading to quick cooling after sundown, but then cooling slows or is halted altogether with moist onshore flow. Therefore, coolest readings in the 30s and perhaps fog will likely be in sheltered valley locations of the north and into portions of the Connecticut River Valley. Warmest readings are likely in coastal ME/NH. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... Southwest flow increases, as will available moisture, in response to an approaching shortwave trough Monday. This ought to lift ceilings in the morning, however widespread status to stratocu cover is expected persist through much of the day. Moisture convergence may be strong enough to produce a brief, light shower on the Mid Coast in the early afternoon. Modestly higher dew points work in through the day, as does warmer 850mb temps at 5-7C, however cloud cover will be the determining factor for high temperatures tomorrow. Should breaks in the clouds allow for mixing and solar insulation, temperatures could easily increase into the low-70`s across the south. Don`t have a ton of confidence in cloud breaks tomorrow however so stuck fairly close to a raw model consensus with higher values closer to MOS guidance across southern NH where cloud breaks are more likely. While deep moisture remains offshore and to the southeast, enough forcing along a crossing cold front Monday evening into the overnight could still produce a few light showers especially across the north and in the mountains of ME/NH. Models and WPC eke out only a tenth or two of rain with the crossing front. && .LONG TERM /TUESDAY THROUGH SUNDAY/... High pressure will briefly build over the region Tuesday. This will allow for mainly sunny and dry conditions. Temperatures will be seasonable for mid October, mainly in the 50s. All eyes then shift towards low pressure moving east from the Great Lakes Tuesday night into Wednesday. 12Z model suite and ensemble solutions continue to a secondary area of low pressure over the Mid Atlantic states late in the day Wednesday. This system will track off the New Jersey coastline Wednesday evening, before racing into southern New England Wednesday night. During this period, rapid cyclogensis occurs with the low plummeting to around 975 mb by the time the center reaches approximately Portland, Maine by early Thursday morning. Heavy rain will fall along and to the left of the H7 and surface low. One to two inches of rainfall expected, however locally higher amounts are possible over the east facing mountains. The Canadian model QPF is at the high end of the spectrum, likely because its track is slightly further east then other model solutions, therefore any dry slotting is delayed. Cloud cover will keep temperatures in the 50s for daytime highs on Wednesday. Cold air advection under gusty westerly winds will keep temperatures in the mid 40s to mid 50s for high temperatures from north to south on Thursday. Breezy conditions will continue into Friday as the low slowly exits through the Canadian Maritimes. Thereafter, high pressure will build into the region over the weekend. This will allow for dry conditions and moderating temperatures. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... Short Term... VFR prevails with light winds for the remainder of today. Tonight, most guidance has consistently pointed toward low stratus development as a likelihood especially over the Mid Coast with weak, moist onshore flow as high pressure shifts into the Gulf of Maine. While some radiation fog is expected to develop tonight over the Connecticut River Valley, patchy dense fog and MVFR or worse (IFR near dawn) ceilings are more likely to develop at coastal and Mid Coast terminals. MVFR, and some brief instances of IFR, ceilings may linger through the day with scattering likely in the afternoon. Then, a cold front crosses tomorrow night with improving conditions to follow as high pressure nudges in from the west Long Term...Increasing clouds expected on Wednesday with rain arriving from west to east Wednesday evening. Will likely see a period of IFR conditions and moderate rainfall along with some wind shear. This ends from west to east early Thursday morning as low pressure moves east. Behind the low expect gusty west to northwest winds of 25 to 30KT especially Thursday morning. Otherwise, we should see conditions improving to MVFR and VFR Thursday and Thursday night, with the lower conditions lasting longest in the mountains. && .MARINE... Short Term...Waves and swells continue to come down tonight with remaining SCAs on track to expire this evening. Light northwest winds turn variable to southerly tonight, becoming southeasterly onshore at 5-15 kts by Monday evening as a wave aloft and associated cold front approaches. The front crosses Monday night with a switch to westerly winds to follow. Long Term...High pressure crests over the Gulf of Maine on Tuesday. The next low pressure system tracks up the East Coast on Wednesday and strengthens rapidly when it reaches the Gulf of Maine Wednesday night. Expect southeasterly winds to back to the northeast Wednesday night. Gale force westerly winds possible on Thursday behind the departing low. && .HYDROLOGY... Low pressure will undergo rapid intensification as it moves quickly to the northeast Wednesday night. One to two inches of rain will be likely as the surface and H7 moves from southern New England to southern Maine. Some of the east facing locations across the higher terrain of the headwaters may have locally higher amounts. This precipitation in such a short amount of time may allow for rapid rises on a few of our rivers. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory for hazardous seas until 6 PM EDT this evening for ANZ150-152-154. && $$ Casey/Cannon

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