Area Forecast Discussion
Issued by NWS Portland, ME

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926 FXUS61 KGYX 202151 AFDGYX Area Forecast Discussion National Weather Service Gray ME 551 PM EDT Fri Oct 20 2017 .SYNOPSIS... High pressure will crest over the region tonight and will shift offshore on Saturday. High pressure will hold off the coast through Sunday. A slow moving cold front will approach from the west on Monday and will stall to the west of the region Monday night and Tuesday as low pressure tracks north through Central New York. Low pressure will continue north into Canada Tuesday night and will drive a trailing cold front through the area on Wednesday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 550 PM...Just made a few minor tweaks, mainly to wind/temps,m based on current obs. Winds are staying up a bit, and so are temps, so just kept temps a little warmer through early evening, before they start dropping off. Previously...High pressure building in from the west will crest over the region by Saturday morning. Aside from a few clouds associated with weak over-running setting up in the north...should a a clear and calm night with lows ranging from the mid 30s north to the mid 40s south. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Fair weather will continue on saturday as high pressure gradually slides offshore. Return flow will bring warmer air back into the region along with a few clouds. Once again high temps will average out well above normal with highs in the north ranging through the 60s. Developing onshore flow will also cap temps in the 60s in midcoast and interior central Maine. Southern New Hampshire and southwest Maine will reach the lower to mid 70s. Looking for variable clouds Saturday night with lows from the mid 30s north to the mid 40s south. && .LONG TERM /SUNDAY THROUGH FRIDAY/... No significant changes to model guidance thru early next week with the 20.12z suite. An anomalous upper ridge will dominate the pattern to begin the period. This trof will get flattened by a s/wv trof traversing the Hudson Bay area...but higher heights and high pressure will tend to hold over the local area thru at least Mon. In all likelihood...deep meridional flow will keep the best rain chances to our W even into Tue. Thru Tue...H9 temps are still forecast to linger around the mid 70s continue in the forecast. Overnight temps should for the most part remain mild in return flow...but Sun night surface ridging should allow for some radiational cooling and I have adjusted MOS temps slightly to account for typical cool spots. The main story of the extended however is the deep trof digging into the central CONUS. Ensemble guidance is forecasting a +3 standard deviation Sly flow to develop. This will not only help to transport the aforementioned warmth Nwd...but also deep moisture. PWAT anomalies approaching 2 to 3 standard deviations above normal by Wed means that it may soon be time to add heavy rainfall wording to the forecast. Based on flow generally parallel to the front...this will be a slow moving event. And one that may also arrive in two waves...with the lead s/wv trof and another with the upper low itself. First with the lead wave...ensemble guidance does indicate a strong H8 LLJ will develop ahead of the front...and deterministic models favor this extended down below 1000 feet. Given how warm it is in the boundary layer...the inversion will be marginal at best based on forecast soundings. Winds could get pretty gusty...especially along the coast early Wed. Beyond midweek...deep trof will close off into an upper low center and that should help to slow everything down. It will also prolong the warmth...and trof axis does not quite make it thru the Northeast. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... Short Term...VFR tonight through Saturday night. Long Term...Widespread VFR conditions into early next week under high pressure. Over the weekend...high center will be closest and so LIFR valley fog is more likely at LEB and HIE. Tue into Wed...deep moisture and WAA over the waters may bring stratus into coastal terminals. While it is too early to say with confidence...some areas of IFR CIGs are possible. && .MARINE... Short Term...No flags. Long Term...High pressure in control of the region will keep winds and seas below SCA thresholds thru early next week. Developing return flow Mon into Tue will gradually build seas outside the bays towards 5 ft Tue. Low level winds increase later Tue and especially overnight into Wed. There may be a small window for gale force gusts outside the bays...and seas will build to near 10 ft. Persistent Sly flow thru the remainder of the week will keep seas above 5 ft even as winds begin to diminish. && .FIRE WEATHER... Relative humidity values will again drop to around 30 percent in southern New Hampshire for a brief period Saturday afternoon but expect winds to be light and variable so Fire risk will be marginal. Expect humidity values to gradually increase on Sunday and Monday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...Cempa/Sinsabaugh SHORT TERM...Kimble/Sinsabaugh LONG TERM...Legro AVIATION... MARINE... FIRE WEATHER... is the U.S. government's official web portal to all federal, state and local government web resources and services.