Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 201539 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1039 AM EST Mon Nov 20 2017 .SYNOPSIS... High pressure building into the region today and tonight will deliver cold temperatures across the region. Expect a brief warm up on Tuesday before another cold front moves through the area on Wednesday bringing a return to colder conditions that should last through Friday. A brief warmup expected Saturday with scattered showers ahead of another approaching cold front that arrives Saturday night. High pressure delivers colder and drier air for Sunday. && .NEAR TERM /TODAY/...
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1030AM UPDATE... Light snow observed across the area this morning is in association with a multi-pronged trough moving through the region with only minor enhancements from upslope flow. The first prong of this trough has moved east, while the second should be arriving in a couple of hours. Thus although most of the light snow has ended now, expect another chance of snow with the next trough axis before the day is over. Like the last round, this one will not be limited to upslope areas only, though total snowfall will be quite light as there is not a lot of moisture to work with. Have adjusted wind gust forecasts today as well since a few areas have had some gusts above 40 MPH. Think that these gusts will be lower as the day goes on, but it will be another windy and cold day. Only minor tweaks to temperature forecast was made. 730AM UPDATE... Morning light is allowing the use of some webcams across NH and a better gauge of where accumulating snow is taking place. I have upped PoP to high chance and likely in most of the high terrain now. This includes some light accumulations into the foothills...especially in Oxford and Franklin Counties. ORIGINAL DISCUSSION... Secondary s/wv trof will cross the area early today. This will renew CAA and allow winds to be quite gusty again during the afternoon. I am not expecting it to be as windy as yesterday...with generally 25 to 30 kt gusts. With favorable dendritic snow growth temps in the low levels and abundant low level moisture...upslope snow showers will continue thru most of the day. Flow also becomes more Wly with time...and that may bring more lake enhanced moisture into Wrn zones. I have expanded slight chance and chance PoP...as well as brought PoP into SWrn NH where lake enhanced bands of snow are drifting a little more Nly than earlier in the night. Froude numbers remain greater than 1 in the CAA regime...so snow showers should consistently be able to top the Green Mtns and drift into Wrn NH...as well as top the White Mtns and sneak into the foothills. Some light accumulations are possible in Wrn NH Nwd thru the White Mtns.
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&& .SHORT TERM /TONIGHT AND TUESDAY/...
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Weak s/wv ridging aloft and surface high to the S trying to nose into the area will allow winds to diminish around sunset. There is a window for some radiational cooling tonight as warm front lifts thru the area aloft and before return flow really picks up in the boundary layer. I have generally stayed with the cooler guidance sources...and also show a small non-diurnal trend late tonight as return flow increases towards dawn. Behind the warm front we also see a much drier low level air mass...which should allow any remaining clouds and snow showers in the mtns to scatter out/dry up. Return flow aloft will also bring in some warmer temps...and allow even shallow mixing to send the Srn and coastal zones on a run to the 50s.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... A warm southwest flow Tue night into early Wed ahead of an approaching cold front. The cold front will move rapidly through the region Wed with scattered showers expected. In the mountains some of the showers will likely change to snow showers as the CAA occurs during the day. Not much QPF is expected with the passage of the front as per models suggest. Models all indicate the heavier band of rain will stay well offshore ahead of the front. Behind the front, a large arctic ridge of surface high pressure will build into the region Wed night through Friday with dry conditions and much colder temps. All models in general agreement about carving out a general broad long wave trof position across the eastern US. This will mean generally colder temps and mainly dry conditions and storm free. The only exception being Sat as a brief warm southwest flow develops scattered showers ahead of the next shot of cold air as the upper trof gets reinforced bringing another shot of cold arctic air across the region by Sunday. && .AVIATION /16Z MONDAY THROUGH FRIDAY/... Short Term...VFR conditions expected to prevail thru Tue. Local MVFR is possible near HIE as upslope SHSN continue for much of the day. Surface wind gusts at or above 25 kts expected this afternoon at all terminals. Winds gradually late in the day and overnight...and shift more SWly. Upslope clouds and SHSN come to an end early Tue as much drier air moves into the area. Long Term...MVFR conditions expected Wednesday as a strong cold front moves through the region. VFR conditions will return by late Wednesday and continue into early Saturday. && .MARINE... Short Term...Currently in a bit of a lull in wind speeds across the waters. That will be short lived however...as a secondary s/wv trof crosses the area today and renews stronger NW wind gusts. Wind gusts will reach marginal gales outside the bays around mid morning...so I have just extended the current gale warning thru this evening. SCA will continue in the bays for the same time. Tue winds becomes more SWly and may allow winds to drop below SCA thresholds...though seas will likely remain near or above 5 ft. Long Term...Southwest flow may approach SCA criteria Tue night ahead of an approaching cold front. The front moves across the waters Wednesday. By Wednesday night a north to northwest flow may briefly reach SCA conditions over the outer waters. High pressure settles over the waters Thursday and Friday with light winds. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ151- 153. Gale Warning until 10 PM EST this evening for ANZ150-152-154. && $$ NEAR TERM UPDATE...Kimble SHORT TERM...Legro LONG TERM...Marine

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