Area Forecast Discussion
Issued by NWS Portland, ME

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870 FXUS61 KGYX 222258 AFDGYX Area Forecast Discussion National Weather Service Gray ME 558 PM EST Sun Jan 22 2017 .SYNOPSIS... A cold front will stall to our south through tonight as high pressure builds by to our north over eastern Canada. A storm system tracking up the coast will bring wintry precipitation to the area late Monday and Tuesday. A cold upper trough will remain over the area through the latter part of the week with a return to colder temperatures. Scattered snow showers in the mountains and foothills can be expected through the latter part of the week. && .NEAR TERM /TONIGHT/...
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6PM UPDATE... Easterly upslope flow on the south side of Canadian high pressure is leading to upslope snow showers on the east side of the mountains. In addition, some showers persist over southern New Hampshire near the stalled front. Have updated the forecast to highlight these areas for the next few hours. Expect the upslope easterly flow in the north to cease producing snow showers in the next few hours as drier air is advected into the area from northern Maine and eastern Quebec. ORIGINAL DISCUSSION... At 19z...the backdoor cold front was situated to our south and west and will remain stalled there through tomorrow. A 1029 millibar high was centered just east of Hudson Bay. GOES imagery showed extensive low clouds across the region. NWS Doppler radar mosaic was showing spotty return over western and southern sections of the forecast area on the cool side of the stalled boundary. For tonight...clearing noted over Quebec province vicinity of the Gaspe Peninsula will try to work south on a cooler and drier north to Northeast flow. Expect we`ll see some gradual clearing overnight over our northern and eastern Maine zones. Elsewhere...we should remain mostly cloudy with onshore flow and the stalled boundary to our south and west contributing to some spotty light precipitation at times. This should be drizzle and eventually flurries as the column cools overnight with some isolated freezing drizzle not completely out of the question. Lows will range from around 20 in the mountains to mid and upper 20s elsewhere.
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&& .SHORT TERM /MONDAY/...
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On Monday...colder and drier air from the eastern Canadian high will continue to nose southward into the forecast area with clouds possibly breaking up for a time as far south as Casco Bay into northeastern New Hampshire. The onshore flow should keep low clouds in place further south and west with some spotty light rain or snow depending on boundary layer temperatures. Cloud cover will advance back north and east during the afternoon as moisture surges back north ahead of approaching coastal system. The leading edge of the steadier precipitation shield should be approaching southern New Hampshire towards early evening. Highs tomorrow will be in the lower and mid 30s...except for upper 20s in the mountains.
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&& .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... ***Significant winter storm to affect the area Mon night/Tue*** A strong trof crossing the Southeast will roll up the East Coast tonight through Tue. Ahead of the lifting trof...an anomalous Ely flow will develop...in excess of -5 standard deviations. This will feed sub-tropical moisture into the region Mon night and Tue. At the same time ridging will increase ahead of the system 00z Tue...most likely due to latent heat release in convection...and allow surface high pressure to build into the Maritimes. This action combined with Ely flow in the lower levels...will set up cold air damming along the Ern slopes of the mtns. Again I have taken the under on model 2 m temps...and feel that much of the event occurring with temps around 32 degrees. Now that does depend on how far S cold air can work behind the cold front today. At 12z...the CAR raob was -11C...colder than any model. Colder dewpoints are also feeding SWwd thru Nrn ME...and having that initial dry air at the surface will enhance any cold air damming. National radar mosaic shows very N/S oriented convection across the Southeast at this time. This is a favorable set up to transport that sub-tropical moisture Nwd...rather than shunting it Ewd. So at this time I am not worried too much about QPF. I feel a good chunk of the area will see at least 1 inch...with near the coastal front up to 2 plus inches. The strong Ely flow and cold dome will likely lead to strong upslope signature to QPF distribution. I enhanced QPF on the SE facing slopes and near the forecast coastal front. This will point towards the Whites and Monadnocks seeing some enhanced precip...and upslope cooling which should help in the wintry ptype. The strong Ely flow will also make for gusty winds. Initially the deeper mixed layer will make it gusty across a lot of the forecast area...but gradually the inversion developing aloft will keep the wind from being too big a deal inland. Very near the coast some gusts to 50 mph are possible...but there was not enough confidence for any high wind watch at this time. Forecast soundings have been showing less mixing and more inversion with time...and the wind signal has slowly backed off with time. Finally the biggest question mark remains warm air aloft. The 22.12z ECMWF remains very cold...and nearly all snow for the forecast area. The 22.12z GFS also stayed on the colder side of guidance...with significant amounts of snow and sleet. The NAM on the other hand...and to a lesser extent CMC...were warm and would lead to more sleet and freezing rain. Given that models typically hold the warm air aloft too long...I blended the 22.12z GFS and ECWMF with the NAM to speed up the warmer air moving in. This gives me more of a snow to sleet for much of the area. Before the mid levels saturate fully...precip could start as sleet most areas...before changing to snow or rain depending on surface temps. With the warm layer on all model guidance between H8 and closer to H7...I have leaned the forecast away from significant amounts of freezing rain and kept it to around a tenth of an inch total. Snow amounts were generated with less than a 10 to 1 ratio...and do carry a large amount of bust potential. More sleet and those ratios could be closer to 3 to 1 or less...and more cold air aloft and we will easily be 10 to 1. With so much uncertainty still...I opted for winter storm watches for a large portion of the forecast area for the potential of 6 inches of snow...along with possibly significant amounts of sleet and some freezing rain. I do envision the areas not in the watch possibly needing an advisory down the road as well. Again the most likely areas to see higher snow totals will be deeper inland where the surface and mid level cold hangs on the longest...and areas where upslope enhanced precip and cooling can help keep ptype snow. Monadnocks...Whites and into the Wrn ME foothills. Warmer air aloft sneaking up thru the CT River Valley and around into areas N of the notches may cut down on snow totals there too. Beyond the storm system the multi-model consensus was used. Generally broad cyclonic flow and NW upslope snow showers will be the dominant precip maker. Temps should average near to above normal. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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Short Term /Through Monday/...Areas of MVFR with local IFR vcnity of KPSM/KCON/KMHT terminal sites. Spotty drizzle and -SHSN psb mainly south of a KLEB to KSFM line along with isolated light freezing drizzle. Long Term...Onshore flow Mon evening will keep BKN to OVC CIGs in all likelihood...with areas of MVFR and local IFR conditions. Precip moves in quickly from the S and a prolonged period of IFR or lower conditions will result in SN/PL/FZRA/RA. Right now warm layer aloft looks rather high...and so PL should dominate mixed ptype...with FZRA being brief in nature. SN is most likely over the far interior...with CON...AUG...and HIE holding onto it the longest. PL will move in from the S and W...with HIE and LEB changing over faster than CON and AUG. MHT and coastal terminals will likely see PL/SN early than change over to RA eventually. PSM/PWM/RKD may also see NE surface wind gusts to 30 or 35 kt at times. Low level moisture lingers much of Tue...and at least MVFR conditions will linger behind the main area of precip.
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&& .MARINE... Short Term /through Monday/...Northeast flow will strengthen through tomorrow with small craft conditions deteriorating to gales by late Monday. Long Term...No change with marine headlines. Storm warnings for the outer waters and gales in the bays. Strongest winds will be during the overnight Mon...gradually diminishing as low pressure passes E of the waters. We will need transitional gales and SCAs on the backside of the system into Wed. && .TIDES/COASTAL FLOODING... Despite being in the low portion of our astronomical tide cycle, large building waves may produce some erosion and splash-over near the times of high tide Monday night and Tuesday. Preliminary storm surge values appear to be around 1.5 to 2 feet with a persistent, strong easterly wind developing. A coastal flood advisory may be needed from the impact of the wave action. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Watch from Monday evening through Tuesday afternoon for MEZ018. Winter Storm Watch from late Monday night through Tuesday evening for MEZ007>009-012>014-019>021. NH...Winter Storm Watch from Monday evening through Tuesday afternoon for NHZ005>011-015. Winter Storm Watch from late Monday night through Tuesday evening for NHZ004. MARINE...Gale Warning from 3 PM Monday to 11 AM EST Tuesday for ANZ151- 153. Storm Warning from 6 PM Monday to 11 AM EST Tuesday for ANZ150- 152-154. && $$ NEAR TERM UPDATE...Kimble SHORT TERM...Schwibs LONG TERM...Legro

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