Area Forecast Discussion
Issued by NWS Portland, ME

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973 FXUS61 KGYX 251126 AFDGYX Area Forecast Discussion National Weather Service Gray ME 626 AM EST Sun Feb 25 2018 .SYNOPSIS... Low pressure tracking through the western Great Lakes will send a frontal boundary eastward toward New England today. This will spread snow, sleet, and freezing rain into parts of New Hampshire and Maine, with a change to rain near the coast. High pressure builds east out of the Ohio Valley behind this system, making it into New England on Tuesday. The next weather maker will be a complex low pressure system arriving Thursday night into Friday which could bring more wintry weather. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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615 am Update: The leading edge of snow has spread into southwest NH as of 6am. The snow will spread rapidly northeast across the rest of NH and southwest Maine by mid morning. Forecast timing still looks good with no changes based on radar extrapolation. Temps along the coast hovering near 32 degrees and the onshore flow continues veering to a more easterly direction which now appears certain to limit snowfall along the immediate coastal areas. All southern and coastal areas will start as snow due to evaporational cooling due to some dry layers in the mid levels but then the developing low level onshore will bring boundary layer temps above critical levels thus changing to snow to rain. Previous Discussion: A fast moving short wave that moves rapidly across the St. Lawrence Valley today will have an associated WAA pattern that will produce widespread snow and mixed precipitation across the region. Ahead of this warm advection pattern there is very little deep cold air in place along with southern areas have little to no snow cover left. This lends to only very shallow cold air damming over coastal and southern areas where it will be wiped out rather quickly allowing the snow to change to rain. Further inland and deeper into the cold air mass enough cold air will hang on to allow for primarily snow to occur. Over coastal areas, boundary layer temps will be marginal and with a developing onshore flow temps will move above freezing by late morning changing the snow to rain. Over interior portions a general area of 2-6 inches is expected with a changeover to some sleet and even some pockets of freezing rain. Winter Weather Advisories have been dropped along the NH seacoast and coastal York counties due to the warmer temps and only light accumulations of snow before the changeover to rain. Have issued additional Winter Weather Advisories for 3-6 inches of snow across northern NH and all the western mountains of ME today. Generally used RFCQPF values which was 1/2-3/4 of an inch and used snowfall accums ratios of 9-10:1.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... The system quickly exits to the east this evening brining and end to the precipitation, followed by clearing later tonight as a dry west flow takes control and continues through Monday. Used model blend temps for tonight and Monday which end up above normal. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Cold air advection will continue Monday night as high pressure builds east from the northern Ohio Valley region. With the absence of Arctic air, temperatures will only drop into the 20s for most areas across Maine and New Hampshire. This ridge of high pressure will slowly move east Tuesday, before slipping off the Mid Atlantic coastline by Wednesday. Temperatures will moderate with time with 40s on Tuesday being replaced by by to lower 50s on Wednesday. It will be mainly dry despite the nearby presence of a cold front over northern areas and the passage of a weak short wave Wednesday night. By Thursday, low pressure will intensify over the Ohio River Valley. Models then diverge as to the intensity and location of the developing storm by Friday. The Canadian model is the furthest south, with the GFS bringing a more robust and impactful system to the region as low pressure retrogrades over Long Island New York. Will lean towards the Euro with a track inbetween other model runs within the 00Z suite. This track would bring a glancing shot of rain and snow to the region with building waves and storm tides over southern areas. Will continue to monitor model trends for this developing active pattern as we will be at the peak for astronomical tides as we enter March. && .AVIATION /11Z SUNDAY THROUGH THURSDAY/... Short Term... IFR/LIFR conditions today into this evening then improving to VFR later tonight and through Monday. Long Term...VFR conditions may lower to MVFR with a weak system passing over northern areas on Thursday. && .MARINE... Short Term... SCA remains in effect for the outer waters as an increasing flow ahead of the system helps to increase wind and waves today with winds diminishing tonight, although seas will remain high into Monday morning. Long Term...Gale force winds are possible late in the week. This will be highly dependent on how far north the developing system tracks on Friday. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Weather Advisory until 8 PM EST this evening for MEZ007>009-012>014-019>021. Winter Weather Advisory until 4 PM EST this afternoon for MEZ018. NH...Winter Weather Advisory until 8 PM EST this evening for NHZ001>004-006. Winter Weather Advisory until 4 PM EST this afternoon for NHZ005-007>013-015. MARINE...Small Craft Advisory until 7 AM EST Monday for ANZ150-152-154.
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