Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 261611 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1211 PM EDT Sun Mar 26 2017 .SYNOPSIS... High pressure crosses the region today. A warm front will approach from the southwest on Sunday before a weak wave of low pressure forms and passes through the Gulf of Maine Monday. This will provide 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 Canada for the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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UPDATE... Have updated the grids based on current conditions. Cold and dry air in place during the midday hours after Canadian high pressure built into the region during the overnight hours. Full sunshine however will allow temperatures to climb into the mid to upper 30s this afternoon. Have adjusted max temps upwards by a few degrees based on current trends. Dew point values will remain very low going into our next precip event tonight as a northerly wind continues over the forecast area for a few more hours. PREV DISC... High pressure over western Maine this morning is allowing some cold and very dry air to filter down into the area. Dewpoints in eastern Maine are solidly subzero early this morning with temperatures in the teens and single digits even into western Maine and northern New Hampshire. As high pressure moves east today, expect an easterly pressure gradient to develop which will promote the damming of this cold, dry air up against the mountains of New Hampshire and western Maine. After a cold start, temperatures will rebound a bit due to a fair amount of sun early in the day. But increasing clouds and continued cold air damming should keep temperatures from rising out of the low to mid 30s for most areas. The GFS model is the most aggressive at developing a period of drizzle/freezing drizzle within the easterly upslope area of New Hampshire this afternoon, but this seems a little overdone and is not supported by most models. The GFS is also the coldest model perhaps in part due to the clouds and light precipitation it develops.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Wave of low pressure ejecting out of the middle Mississippi Valley today will move toward our area tonight. Expect an initial round of light precipitation, probably snow, to move through the area during the evening as warm advection begins aloft. More persistent precipitation will begin arriving later in the night. At this point, temperatures aloft will be warming to above freezing for at least part of the area, while low level temperatures remain near or below freezing. This will cause precipitation type to change to freezing rain over southern and western parts of the area. Expect ice accumulations from just a light glaze to as much as a quarter of an inch by morning across central, southern, and western New Hampshire. Models are now indicating the development of a secondary surface low over southern New England on Monday, tracking east into the Gulf of Maine. This development will have the effect of keeping the cold air locked in place across western Maine and eastern New Hampshire. In fact, this cold air could be deep enough for some sleet across interior western Maine which will limit total ice accumulations there a bit. As the low and parent trough move east on Monday, expect precipitation to come to an end from west to east during the afternoon or evening, possibly lingering a little longer in the western Maine mountains. A mix of Winter Weather Advisories and Freezing Rain Advisories have been issued for the area to draw attention to the expected wintry conditions. The freezing rain will be the primary hazard here considering its impact on travel. The Advisories were structured so that Winter Weather Advisories were used for areas which are expected to get an inch or more of sleet and snow in addition to the freezing rain, while areas expected to get less than an inch of snow and sleet were given a Freezing Rain Advisory to highlight the more significant hazard. There is still a lot of uncertainty with regard to precipitation type. It is late March after all, and this is not a climatologically favored time for freezing rain, especially during the day. However, it`s also not that common to see such a dry/cold air mass either. The model forecast easterly flow will serve to pile up this cold air against the North-South mountain ranges of New Hampshire, locking the cold air in place and allowing it to drain southward. The development of a secondary surface low tracking to the south of the area serves to increase confidence in the low level cold air damming, but also raises the possibility that precipitation may fall as more snow/sleet as deeper cold air is pulled in to the north of the low. This is a particularly challenging forecast and it will be worth it for users to monitor the forecast for updates and changes as the event begins. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... 500 mb flow trends from weakly to more moderately amplified during the extended range, and will be highly dependent on stream of closed lows moving to the Western and Southwestern United States before lifting NE toward the Great Lakes and Northeast. These will ultimately determine how amplified flow becomes and timing of troughing and ridging. Blocking over Europe should allow for deepening troughs to our east. The one positive is that this will allow the coldest air to shift back toward the pole, and while we may not see too much in above normal temps, they will shift more toward normal thru the period. Monday night remains tricky, mainly in the northeast where temps may remain below freezing through the night with some freezing rain expected, although mounts should be light. Could also see some snow or sleet mix in at times, given some colder air moving in aloft as the low intensifies a little over the Gulf of Maine. Elsewhere precip may see a break late Monday night as warm sector aloft moves in, but onshore flow may allow some drizzle to persist on the coastal plain. Tuesday will see another weak low shift south of the region, further offshore than than the previous low. It will drag a cold front across the region, which could produce another round of showers Tuesday afternoon/evening. Could see some spots in southern NH break out into the warm sector before this front comes thru, in which case they may see temps 50 or higher. Once the front goes thru Tuesday night, will see colder air aloft and some snow showers will be possible. The front will wipe out the occlusion and marine layer, so Wednesday will be warmer than Tuesday in many spots with highs in the 40s to low 50s. Thursday will be a little cooler than Wednesday, but coldest air aloft will have moved through already. Temps warm up a little bit more on Friday, with next system approaching Friday night and bringing a chance for precip Friday night and Saturday. May start as some wet snow in some places, but should be rain during the day Saturday. && .AVIATION /16Z SUNDAY THROUGH THURSDAY/... Short Term...Conditions start VFR today with very light winds. But expect increasing clouds from southwest to northeast as the day goes on, and by evening ceilings will begin lowering to MVFR. Light snow changing to sleet and freezing rain from southwest to northeast is expected tonight into the day Monday with IFR conditions expected. There is still a great amount of uncertainty on precipitation type, but freezing rain is possible at all terminals for at least some time, possibly lingering into the afternoon on Monday at Augusta. Eventually temperatures will warm above freezing and cause precipitation to change to rain. Long Term...IFR or lower Monday night and Tuesday with RA/FG/DZ. May see some improvement to MVFR During the day Tuesday at KMHT/KCON. Some improvement to MVFR everywhere Tuesday night with VFR Wednesday-Thursday. May see NW wind gusts to 25 kt at times on Wednesday. && .MARINE... Short Term...Light winds and low seas are expected over the Gulf of Maine as high pressure crosses the waters today. A southeast flow will develop ahead of a developing surface low on Monday, and this flow could bring some higher seas and possibly some wind gusts to 25 KT late Monday. Long Term...Seas could reach 5-6 feet in swell from coastal lows Monday night and Tuesday. Winds will reach SCA levels in NW flow behind a cold front Wednesday, perhaps lasting into Thursday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Weather Advisory from 8 PM this evening to 5 PM EDT Monday for MEZ007>009-012>014-018>022. Winter Weather Advisory from 8 PM this evening to 10 AM EDT Monday for MEZ023>028. NH...Winter Weather Advisory from 8 PM this evening to 5 PM EDT Monday for NHZ001>004-006-009-010. Freezing Rain Advisory from 8 PM this evening to 10 AM EDT Monday for NHZ005-007-008-011>015. MARINE...None. && $$ NEAR TERM...Cannon SHORT TERM...Cannon LONG TERM...Schwibs

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