Area Forecast Discussion
Issued by NWS Portland, ME

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830 FXUS61 KGYX 210532 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1232 AM EST Sun Jan 21 2018 .SYNOPSIS... A weak cold front will drop south from Canada tonight and will stall over southern New England Sunday and Sunday night. The front will lift north on Monday and Monday night as a warm front. Low pressure will track northeast through the ST Lawrence Valley on Tuesday and will drive a cold front through the region in the afternoon. A trough of low pressure will linger over the region Tuesday night and Wednesday. High pressure will gradually build in from the west Wednesday through Friday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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1232 am Update: Have updated the forecast to account for low cloud cover over northern areas, stretching east to the Midcoast region. Mainly high, thin clouds over southern sections. Have added some fog to the Keene area for the next few hours. 945 pm Update: Ingested latest data for ESTF with only changes being made in the cloud grids. Satellite imagery shows band of clouds across mountains east into central Maine so made appropriate adjustments to reflect more cloud cover across those areas and further south as the area drifts south later tonight. 7 pm Update: Ingested latest obs data for ESTF. No changes needed at this time. Previous Discussion: Weak cold front will gradually sag south from Canada tonight. This boundary already re-enforcing cloud cover in northern zones and may produce a few snow showers later this evening in the usual upslope areas in the mountains. Expect any accumulations to be light and spotty. Remainder of the region will see variable high and mid level clouds. Lows overnight will generally range through the 20s from north to south.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... Cold front will gradually stall over southern New England on Sunday. Will see varying amounts of cloud cover through the day but temperatures will still top out above normal as cooler air remains north of the region. Highs will range through the 30s north and lower to mid 40s south. Clouds will thicken Sunday night as the front begins to lift north as a warm front. Aside from a few snow showers in the mountains most of the forecast area will see a dry night. Lows will range through the teens in the north and 20s south. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... Focus in the extended continues to be on Mon night/Tue system. Not much significant change in available guidance today...with a wave moving into CA today amplifying into the MS River Valley by Mon. High pressure build build out ahead of it to the N...while WAA surface and aloft drives a warm front towards New England. The devil is in the details of where that warm front hangs up at the surface...because it appears that the mid level front should make appreciable progress thru the forecast area. Given the high pressure positioning...I have stayed below guidance temps and near the previous forecast. GEFS and ECMWF EPS guidance continues to show mean surface primary low headed for the the Ern Great Lakes...with a secondary redeveloping across New England. My feeling is that this mean secondary is too far inland...and will likely end up developing closer to the coast. That being said...it will likely be farther N than is necessary to keep really cold air in place. But it will delay the warm up a bit. An examination of all ensemble guidance clustered together shows that with the 20.00z suite stronger high pressure located to our NE...or colder scenarios...were favored when there were higher heights ahead of the developing wave across the Intermountain West. This is possibly a result of maximum primary intensity occurring earlier...and strongest conveyor belts maturing and weakening before arriving across the Northeast. The 20.12z GFS and ECMWF so far have initialized too low with heights ahead of the wave...and we will have to see if those trends continue. The important window will really be tonight into early Sun to see how features are developing. The resulting forecast for our area will be a light snow or mix at onset...turning into a break in precip as the dry slot moves into the area. There could be a period of drizzle or freezing drizzle...but I did not want to complicate the forecast more than it already is. Steadier precip moves in Tue...and it will likely bring a mixed bag of some snow in the mtns...with sleet...freezing rain...and eventually rain for more Srn and central locations. Snow amounts will be light...especially outside the mtns...with freezing rain amounts looking like less than a quarter inch as well. Beyond this system...after CAA midweek...a gradual moderating trend to milder than normal will develop. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... Short Term...VFR tonight and Sunday with areas of MVFR ceilings in the mountains. Areas of MVFR ceilings develop Sunday night as onshore flow sets up. Long Term...VFR begins the period. Heading into the afternoon...some weak forcing may allow for some light precip to develop. It appears a dry slot moves in Mon night...but gradually warming and moistening air mass will lead to widespread IFR conditions developing. Downsloping winds may keep HIE MVFR or VFR into Tue. Steadier precip moves in Tue...which may begin as a PL/FZRA mix at all terminals before changing to RA...especially near the coast and across Srn NH. IFR or lower conditions linger into Tue evening before Wly flow scatters out clouds. && .MARINE... Short Term...Continuing SCA`s through tonight for the outer waters. Long Term...Sly winds will begin to increase Mon...and especially into Tue as low pressure moves thru New England. A period of gale force winds gusts is possible outside the bays as the core of the low level jet moves overhead Tue. SCA conditions will likely linger thru the end of the week...as CAA follows the system and winds and seas slowly diminish. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...Small Craft Advisory until 6 AM EST early this morning for ANZ150-152-154.
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&& $$ JC

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