Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 251129 AFDGYX Area Forecast Discussion National Weather Service Gray ME 729 AM EDT Sat Mar 25 2017 .SYNOPSIS... A cold front shifts south of the region today and stalls there, producing some rain and snow over southern New Hampshire. High pressure builds in tonight from the north and will shift east on Sunday. A warm front will approach from the southwest on Sunday and cross the region Sunday night, providing a round of mixed wintry precipitation Sunday night into Monday. Low pressure moves north of the region on Tuesday and drags a cold front through on Wednesday. High pressure will build in from the west for the end of the week. && .NEAR TERM /TODAY/...
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730AM UPDATE... Have updated the forecast based on early morning temperatures. Although the wind shift with the cold front has moved through to southern New England, the cold air is really only being felt across the state of Maine where temperatures have actually fallen below freezing. Elsewhere temperatures have remained above freezing tonight. ORIGINAL DISCUSSION... A cold front is sliding southward early this morning, and has made its way to near the Massachusetts line already. This will bring a light northerly wind today with some drier air. Meanwhile, a mid level shortwave trough will squirt eastward over the top of a sharp ridge over the eastern Great Lakes and move through southern New England during the day today. This will provide another round of precipitation, primarily to southern New Hampshire. As precipitation arrives, once again expect temperatures to cool and precipitation to quickly become snow. Some light accumulation is possible, but temperatures are expected to be near or above freezing which should prevent significant accumulation. If all of the forecast QPF accumulates as snowfall, then it is possible that up to 2 inches could accumulate, but again we expect it to begin as rain and temperatures to be near or above the critical melting point which will limit accumulations to under an inch after the change over. Further to the north and east across the eastern part of the forecast area, temperatures will warm into the low to mid 40s this afternoon and stay dry.
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&& .SHORT TERM /TONIGHT AND SUNDAY/... High pressure shifts over the area tonight which will allow winds to go calm with good radiational cooling conditions. How low we go will depend on the amount of low level moisture. It looks like at least northern areas will have enough dry air in place to allow temperatures to drop into the single digits, while southern New Hampshire and coastal Maine may only drop into the 20s. As the high shifts east on Sunday it will set up an easterly low level flow across New England. This type of flow promotes cold air damming to the east of the mountains. With cold temperatures expected to start the morning, the damming should keep the temperature from warming all that much across eastern New Hampshire and coastal/interior Maine. By Sunday afternoon, the onshore low level flow may bring enough moisture to produce some light drizzle or freezing drizzle, mainly over eastern New Hampshire and southwest Maine. The temperature is expected to be fairly close to the critical 32 degree mark, so will need to be alert for the potential for light icing to occur. Models would like to warm temperatures above freezing Sunday afternoon, but with a cold air dammed flow that may not happen. Have lowered forecast temperatures below model guidance to account for this. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... At 500 mb, coldest core of air sits north of Labrador through the weekend, with troughing shifting eastward across far northern Maine tonight and Sunday. Several weak waves will move through zonal flow behind this system from Sunday through Wednesday, before a larger trough closes off east of the Maritimes at then end of the week. The good news is that the coldest air retreats poleward, and the bad news is we have to deal with several bouts of precip for the early to mid week. Sunday night and Monday is the trickiest part of the forecast as a warm front aloft lifts through the region in response to a weak low tracking out of the Great Lakes and up the St Lawrence Valley. The question is to what extent the cold air damming will keep cold air locked in at the surface since surface ridge tends to be located more to our east than northeast in classic damming situations. Flow may end up more onshore, especially along the coast, as surface gradient is more southerly, but initially weak. This may keep coastal areas above freezing Sunday night, but it will be close. Inland areas will probably be just below freezing, and with nearly isothermal profiles, may see a little of everything when it comes to precip. Still, precip amounts should be relatively light, and given a combination of snow and freezing rain, perhaps even some sleet, will likely make for a messy commute Monday morning. On Monday, the southerly gradient tightens and expect to see temps rise above freezing most everywhere, with rain likely through the day. By Monday night, very weak low wants to form over the Gulf of Maine and this will likely kill any damming but will also weaken the flow a bit. Could see some freezing or frozen light precip or drizzle develop over inland areas again, although coastal areas should remain above freezing. By Tuesday, any sense of damming will be gone and temperatures aloft rise to around 5C, so should surface temps rise well above freezing everywhere, although clouds and showers are likely to linger as low level flow remains weak and cold front hangs back. The first cold front shifts through late Tuesday and may produce a round of showers with a secondary cold front moving through Wednesday looking mostly dry. Temps behind the system drop to near -10 C at 850, but only for a day. Thursday looks fair but still a few degrees below normal. Next system approaches Friday, with the best chance of chance of any precip not until Friday night. && .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/... Short Term...Cold front which dropped through early this morning has improved conditions to VFR for most areas and cleared out the brief fog. Another round of light rain and snow is expected again today, primarily over southern New Hampshire. Conditions could become IFR at times in the snowfall with MVFR ceilings possible as far north as Portland. Precipitation ends tonight with a return to VFR conditions. Long Term...Flight restrictions look to be in the forecast Sunday through Tuesday night, and will probably be IFR or lower Sunday night through Monday night. Expect some improvement to MVFR Tuesday and Tuesday night. VFR expected by Wednesday. Some light FZRA expected Sunday night into Monday morning, especially away from the coast. && .MARINE... Short Term...Light winds are expected over the waters as high pressure crosses the region through Sunday. Long Term...Weak low pressure developing over the waters Monday should keep winds below SCA levels, but as the low shifts east Tue-Wed, will see NW flow pick up and may need SCA Tue night and Wed. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ LONG TERM...Cempa

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