Area Forecast Discussion
Issued by NWS Portland, ME

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638 FXUS61 KGYX 062115 AFDGYX Area Forecast Discussion National Weather Service Gray ME 415 PM EST Tue Dec 6 2016 .SYNOPSIS... High pressure moves off to the east tonight while an elongated trough of low pressure moves into New England from the west by morning. This will spread some light snow into parts of the area around the morning rush hour, but accumulations are expected to be very light. A slow moving upper level low pressure system will move through southern Canada Thursday and Friday, spreading some snow showers into the mountains. This will also drive a cold front through the area later on Friday bringing much colder weather for the weekend. && .NEAR TERM /TONIGHT/... Regional radar shows precipitation spreading through northeast Pennsylvania and northern New Jersey as of around 3PM. This is in association with a shortwave trough and developing surface low pressure tracking through the Mid Atlantic states. This feature is expected to move east to the south of New England tonight into Wednesday, while another spoke of energy rotates around the upper level low currently over Minnesota and moving into the Great Lakes. Northern New England will be caught in between these two diverging systems, with some of the moisture associated with the southern one being pulled northward into the upper low. As a result, we expect that as precipitation moves in from the southwest during the early morning hours, it will decrease in intensity and eventually dissipate as it moves east. For tonight, high pressure moves east while high level cirrus clouds begin moving in from the southwest. With high pressure over eastern parts of the area for the first part of the evening, expect pretty good radiational cooling conditions especially considering the snow cover. Although clouds will be increasing with time, as recent history has shown us these high level clouds do not have near as much of an insulating effect as lower clouds would. Temperature forecast tonight will be quite tricky, as temperatures will likely level off around midnight or possibly rise a bit over New Hampshire as clouds increase and light snow moves in. Temperatures will range from the upper teens in the east to the upper 20s in the southwest. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... Light snow should have begun moving into New Hampshire by Wednesday morning. Given the disconnect between the two diverging systems, expect total precipitation amounts to be fairly light. Precipitation type should be mostly snow, though temperatures will warm as precipitation ends and there could be some sprinkles of light rain as precipitation ends. Total snowfall amounts should be around an inch or less, with even lesser amounts further to the east. Should see some breaks in the clouds Wednesday night to the south of the mountains which will allow temperatures to fall back into the mid to upper 20s for most of the area. && .LONG TERM /THURSDAY THROUGH TUESDAY/... The general pattern in the extended is a wintry look. The 06.12z GEFS and ECMWF EPS agree on a few key features. Probably most importantly being ridging thru AK and the Arctic...pushing the cold air Swd into Canada. The proximity to the CONUS gives us a better chance at seeing at least modified pieces of that air mass. This is evident in the tendency for both ensemble suites to favor trofing across the Northeast. For example...the 06.12z ECMWF EPS keeps all of Nrn New England below 0C at 850 mb thru the end of the run. At the same time there is a faint signal for Southeast ridging...which should act to keep the storm track in our neighborhood. More specifically...Thu will begin the step down as a cold front crosses the forecast area. Upslope snow showers should be most prevalent...though a scattered flurry downwind of the mtns is possible. The upper trof axis lags back until early Fri...and another round of upslope snow showers and scattered flurries is likely with this feature. Cool NW flow and upslope snow showers continue thru the first half of the weekend. Sat night high pressure builds in...and could set the potential for a very cold night. With mid level temps in the negative teens to near minus 20 it has a shot at the coldest night of the season for many...including some sub-zero readings in Nrn zones. For now blended a little towards MEX guidance as the change in air mass and slightly anomalous nature will make the multi-model blend struggle to catch up. I say slightly anomalous because current forecasts are around one standard deviation below normal...cold but not really pushing records or anything. Attention will then be on late Sun into Mon. A strong trof moving thru the flow will be the next precip maker. Model guidance is aggressively dropping the polar vortex thru the Canadian Prairies and sending cold air Ewd...while this storm system is consolidating over the central CONUS. I am leaning on the cooler side of guidance for this system...especially in the Nrn zones. There is a mixing risk for areas south of the mtns and near the coast...but it is too early to get that detailed in the grids. For now kept things at a rain/snow mix for areas where warmth surface and aloft would be most likely to creep in. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Short Term...VFR conditions should prevail through most of the night, but cloud heights will be decreasing from southwest to northeast by morning. Some light snow is possible as well, mainly at Lebanon and Whitefield, but minor accumulations are also possible at Concord and Manchester. Should see MVFR ceilings areawide on Wednesday as flurries or light snow track across the area. Some improvement to VFR is expected to the south of the mountains Wednesday night. Long Term...In general cold and dry NW flow is expected for the majority of terminals thru the weekend. The best chance for more widespread precip will be with the passage of the main upper trof. SHSN will be possible at all terminals...but most likely for HIE where upslope flow will enhance coverage. The upslope flow will keep MVFR or lower conditions lingering around HIE into Sat before high pressure builds in overnight. && .MARINE... Short Term...Light winds expected over the waters as a very weak trough moves across the Gulf of Maine late on Wednesday. Wave heights should remain quite low as well. Long Term...A series of cold fronts are forecast to cross the waters late in the week. This will bring about a long duration NW flow. This should allow seas to build above 5 ft on the outer waters...and a period of 25 kt gusts for all waters late in the week into Sat. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Kimble SHORT TERM...Kimble LONG TERM...Legro

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