Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 211632 AAB AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1232 PM EDT Wed Mar 21 2018 .SYNOPSIS... Low pressure will pass offshore south of New England today and will slowly move northeast into the maritimes by the end of the day on Thursday. A trough of low pressure will linger over the area on Saturday. High pressure will build in from the north Sunday and Monday and will hold over the area on Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Update...Nly drain of dry air continues to eat away at the leading edge of precip across Srn New England. Lead S/WV trof is already shearing out to our ESE...and I expect that precip is going to lose some of its Nwd momentum this afternoon. I have backed off PoP delay timing until after 00z for most areas. The trailing S/WV trof...currently crossing the a little more dynamic and will be the focus of cyclogenesis this evening. While overall the forecast soundings are a little dry and forcing for ascent a little ragged...there are signs around 06z that the best overlap of lift and RH will combine for a several hour window of decent snow growth and snowfall. The forecast mid level low tracks are actually in good position for snowfall in the forecast area...but the combination of confluence and feeding of dry air is going to limit the Nwd extent of steady/accumulating snowfall. Combined with the ECMWF EPS suggesting meager probabilities of 3 or more inches across most of the forecast area...I am hesitant to bite on some of the high QPF/amped hi-res guidance. A model blend hedging more towards the ECMWF camp looks reasonable...and has adjusted snowfall amounts down about an inch. No changes to headlines are planned. Previous discussion...Dew point depressions continue to be significant indicating very dry air draining south from northern Maine and New Hampshire. This dry air will determine how far north the precipitation will reach tonight, limiting any potential snowfall to southern areas. Prev Disc... There remains significant disagreement with guidance within the 00Z model suite. The battle between a complex system passing to our south and plenty of dry air over interior Maine and New Hampshire will continue through early Thursday. GYX 00Z sounding continues to show this very dry air in place. There are significant dew point depressions across the region as well. A double barrel surface low will elongate with time, making for a northeast to southwest orientation to the precipitation field later today. The precipitation will attempt to back into the region towards sunset as it fights the dry air to the north. A conveyor belt of cold dry air will develop with a north to northeast wind. This will allow for maximum temperatures today to be slightly below most available guidance as clouds increase, thicken and lower during the day.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Euro and the Canadian remain relatively light on the precipitation, while the NAM and GFS solutions suggested warning criteria for portions of the coastline. Played it down the middle and will be issuing winter weather advisories for southernmost sections. The headlines will match up well with adjacent offices. Having said that, this remains a low confidence forecast. Expect 2 to 4 inches snowfall, mainly along the coast tonight. Have brought the precipitation into the region early this evening for timing purposes. Mesoscale models suggest the precipitation may enter southern areas later this afternoon. However, will lean heavily on the sublimation potential with the dry air in place. Very light additional accumulations of snow (mainly eastern areas) are expected Thursday morning as the double barrel surface low finally organizes into one system and heads towards the Canadian Maritimes. No significant clearing expected with the upper level trough remaining in place overhead. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Cyclonic flow will persist over the region Thursday night into the weekend as secondary upper trough digs into the northeast. Looking for partial clearing Thursday night as low pressure pulls off to the northeast. Lows will generally range through the 20s. Any morning sun will give way to clouds Friday as upper trough moves in from the west and low level moisture rotates in from the east. Highs will average out near normal ranging through the 30s to near 40. More of the same for Friday night and Saturday as upper low slowly shifts east. Looking for mostly cloudy skies through the period with a few snow showers possible on Saturday. Lows Friday night will range through the 20s and highs Saturday will range from the mid 30s to lower 40s. After variable clouds Saturday night looking for clearing skies on Sunday as high pressure builds by to the north. Temperatures will range through the 30s from north to south. High pressure will continue to build over the area Sunday night into Monday. Looking for clear skies and light winds with temperatures near normal. High pressure will remain parked over the area monday night and Tuesday with temperatures moderating slightly. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/... Short Term...Conditions gradually lowering to MVFR this afternoon, followed by IFR and LIFR, mainly over southern areas. Higher ceilings over central and northern areas. Gradual lifting of the ceiling and visibilities Thursday afternoon. Long Term... VFR with areas of MVFR ceilings Thursday night through Saturday. VFR on Sunday. && .MARINE... Short Term...Have issued gale warnings for Casco Bay as well. Therefore, all of the waters will be in a gale at some point during the storm. Long Term... SCA`s to minimal Gales possible Thursday night. Sca`s likely Friday through Sunday. && .TIDES/COASTAL FLOODING... A tidal anomaly at close to a half foot and an additional two foot storm surge are expected tonight near the time of high tide. This will combine with building nearshore waves of 10 to 15 feet to produce generally minor beach erosion and splash- over flooding near the time of high tide tonight. Pockets of moderate impacts are possible, due in part to the damage of sand dunes and infrastructure from the storms earlier this month. Astronomical tides peak out as well tonight. There will also be coastal flooding with up to a foot of water on the side streets near Portland Harbor and near Marginal Way. Flooding can also be expected along Granite Point Road in Biddeford and the Backbay area of Hampton. Some streets in Portsmouth may have minor flooding. Areas that have splash-over will have also some flooding due to the pooling of water landward of the dunes. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Weather Advisory from 7 PM this evening to 11 AM EDT Thursday for MEZ023>028. Coastal Flood Advisory from 1 AM to 5 AM EDT Thursday for MEZ023-024. NH...Winter Weather Advisory from 7 PM this evening to 9 AM EDT Thursday for NHZ012>015. Coastal Flood Advisory from 1 AM to 5 AM EDT Thursday for NHZ014. MARINE...Gale Warning from 6 AM to 5 PM EDT Thursday for ANZ153. Gale Warning until 5 PM EDT Thursday for ANZ150-152-154. Gale Warning from 6 PM this evening to 5 PM EDT Thursday for ANZ151. && $$ NEAR TERM...Legro is the U.S. government's official web portal to all federal, state and local government web resources and services.