Area Forecast Discussion
Issued by NWS Portland, ME

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604 FXUS61 KGYX 131535 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1035 AM EST Wed Dec 13 2017 .SYNOPSIS...
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Behind the departing low pressure a strong cold front has moved through the region. Snow showers persist in the mountains today. Temperatures today will likely fall through the day...ending up the teens by the evening. Wind gusts in excess of 35 mph will make that air feel bitterly cold. The coldest air of the season will move into the region behind this system for the remainder of the week...with a few chances for additional snow showers.
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&& .NEAR TERM /TODAY/...
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1030AM UPDATE... Have updated the forecast primarily to tweak PoP and temperatures based on latest observations. Front has cleared the area but upslope snows continue in the mountains. This may decrease in coverage this afternoon when flow becomes more well mixed. Additional accumulations are possible, so will maintain ongoing Winter Storm Warnings. 730AM UPDATE... Bulk of the precip outside of the mtns has moved E of the forecast area at this hour. Minor adjustments to temps and dew points. Otherwise no significant change to the forecast. ORIGINAL DISCUSSION... Upper low pressure is beginning to approach Northern New England this morning. At the moment lift ahead of it...along the H8 cold front...is leading to a band of precip across the Midcoast. I have increased PoP to likely...and have a mixed bag of ptypes. There may be some rain along the immediate coast where warmer air still lingers...but inland temps at or below freezing are probably leading to a little bit of everything with mid level temps still just above freezing. This will be short lived precip however...as the surface low moving into Downeast ME will drag precip with it. The upper low itself will likely provide for fairly widespread precip early in the day. The cooling column will support snow showers vs mixed precip by then though. The real cold air will move into the region behind the trof axis...which will also help mix down stronger winds aloft in CAA. There does appear to be a window of possible 40 kt gusts from about 21z to 00z. Given the recent snow and ice...tree limbs may be more susceptible to breaking and leading to power outages...so I have issued a wind advisory for Southern NH and adjacent SW ME. Elsewhere gusts of 25 to 30 kts are likely in the afternoon. The developing strong W winds will also help to focus snow showers in the higher terrain. Very low snow growth zones...lingering low level moisture...and orographic lift will likely result in numerous snow showers...and efficient snow accumulation despite low QPF. Several inches additional accumulation are possible today...and given that there is no discernible break in snow for the mtns...I have extended the winter storm warnings thru the evening for those areas. Given the well mixed boundary layer...snow showers may be able to top the mountains and move downstream...but significant accumulations are not expected there.
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&& .SHORT TERM /TONIGHT AND THURSDAY/...
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Chilly night on tap...especially considering the gusty W flow that will be continuing. Temps will fall into the teens S of the mountains...where downsloping and a well mixed boundary layer will keep readings relatively mild considering the air mass moving in. In the mountains and N readings will bottom out in the single digits. With winds staying gusty overnight...wind chills will fall to as cold as -10 in the northern zones...and to near zero S of the mountains. Cross barrier flow...cold temps...and lingering low level moisture will keep snow showers going along and upwind of the mountains as well...though coverage should be less widespread than the afternoon. On Thu a trailing S/WV trof will pass S of the forecast area. Though at this time it looks far enough S to avoid significant impacts...it will likely spread some cloud cover into southern zones...and may even bring a period of very light snow to southern NH. The main story however will be the cold temps...with afternoon highs staying in the 20s S of the mountains...and teens and even single digits in the higher terrain.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... The mean long wave trof position remains anchored across the eastern US while the high amplitude ridge across the west coast remains in place. The coldest air of the season will move into the region with this long wave trof as a series of clipper systems move through this long wave trof over the outlook period. These clipper systems will each have very limited moisture due to their source region, but enough to allow scattered snow showers and reinforcing shots of arctic air in their wake. The first of these systems will arrive Fri night and exit by late Sat. Then another similar clipper Sun night into Mon. Generally stayed very close to superblend models for the outlook period. One item to note, min/max temps may not be cold enough for Thu night through Fri night due to the fresh snow cover. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
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Short Term...SHSN will be likely in the mtns...with LEB and HIE possibly seeing local IFR or lower conditions thru the day. Scattered SHSN are less likely downwind of the mtns...but it cannot be ruled out. In addition after 18z thru about 00-01z surface wind gusts at or above 30 kts are possible at all terminals...especially across southern NH and MHT/PSM/CON. Gusty W winds will linger into Thu. Long Term...VFR conditions except MVFR/IFR in any snow showers with the next clipper system to move through the area Fri night and Sat.
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&& .MARINE...
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Short Term...A strong cold front is expected to cross the waters today. Strong W winds will develop in the CAA behind the front...with gale force gusts expected for all waters. A strong gale is possible outside of the bays. Winds will diminish in the bays this evening...but gale force gusts will linger outside the bays thru the overnight. Winds and seas will remain above SCA thresholds thru Thu. Long Term...Strong gusty west winds continue into Thu night due to the combination of strong CAA over the warm waters and the pressure gradient. High pres beings to settle south of the waters Fri allowing winds to diminish. A strong northwest flow develops with possible gale force winds once again in the wake of the next clipper system which exits off the coast Sat night.
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&& .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Wind Advisory until 9 PM EST this evening for MEZ018-023. Winter Storm Warning until 7 PM EST this evening for MEZ007>009. NH...Wind Advisory until 9 PM EST this evening for NHZ008>015. Winter Storm Warning until 7 PM EST this evening for NHZ001>003. MARINE...Gale Warning until 11 AM EST Thursday for ANZ150>154.
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&& $$ NEAR TERM NEAR...Kimble SHORT TERM...Legro LONG TERM...Marine

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