Area Forecast Discussion
Issued by NWS Portland, ME

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263 FXUS61 KGYX 101657 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1157 AM EST Sun Dec 10 2017 .SYNOPSIS... In the wake of a departing ocean low, upslope snow showers can be expected across the mountains. Otherwise, dry weather is expected through Monday for most of the area. The next low pressure system will affect Maine and New Hampshire Tuesday with another round of wintry precipitation. Cold and windy conditions are then expected midweek. Another low pressure system could affect the region at the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1155 AM...For this ESTF update minor adjustments to near term grids to reflect the current mesonet. Prev disc... 900 AM...at 13z a 983 millibar low was vicinity on Newfoundland. An arctic boundary extended from the Gaspe Peninsula through the upper Great Lakes. For today...westerly trajectory to the lee of Lake Ontario and upslope flow will produce varying amounts of clouds across the forecast area. Snow showers and light accumulations should be confined to the higher terrain. Highs will be 25 to 30 along the international border and in the 30s elsewhere...but increasing westerly winds of 10 to 20 mph will make it feel several degrees colder today. For this ESTF update...I adjusted near term grids to reflect current mesonet and GOES satellite trends. Prev Disc... 650 AM Update...Little change to the going forecast. Just a few minor adjustments to clouds and temps at this time. Other than some leftover flurries and upslope snow showers, this snow event is in the books. We have received reports of 3 to as much as 8 inches at this time. Previously... Low pressure continues to rapidly move away from ME and NH early this Sunday morning with snow ending quickly from S to N. Have cancelled all the advisories at this time. Otherwise, we expect gradual clearing today outside of the mountains. Upslope snow showers are likely to continue today - mainly in Coos County NH. Otherwise, gusty westerly winds will be the norm today in the wake of the low with high temperatures getting above the freezing mark to the east of the mountains.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Another short wave trough will approach from the west tonight. This will aid in increasing chances for snow showers in the mountains. Elsewhere, increasing clouds are likely with a few flurries possible. SFC low pressure development will likely take place over Downeast Maine during the day on Monday in response to the passing short wave trough. However, it is likely to be a late bloomer and allow much of the forecast area to be dry. However, there is a possibility that Midcoast zones may see a period of snow showers. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... High impact weather: High confidence of accumulating snowfall Tuesday Overview: A persistent pool of cold air over northern Quebec and Hudson bay region will keep a trough over the eastern portion of the CONUS through the end of the week. A series of short waves will bring a chance for snow to the region every few days with cyclonic flow and cool temperatures between the storms. Monday night - Tuesday night: Low pressure moving out of the Great Lakes will bring widespread snow to northern New England on Tuesday. Monday night will see temperatures drop to the single digits north to mid teens south as weak high pressure remains to our east. Increasing cloud cover through the night with the approaching low will likely keep temperatures from dropping quite as cold, but any portions of the area which are still clear could drop quite rapidly at sunset. Precipitation will begin around daybreak and continue throughout the day on Tuesday as the surface low begins to track up the St. Lawrence valley. With the cold air in place snow is the clear precipitation type through the morning hours. By midday a secondary low begins to take hold over Nantucket. This low will intensify somewhat as it tracks parallel to the coastline up the Gulf of Maine through afternoon. Since last night we`ve seen a trend for the coastal low to take over as the primary low, which is consistent with climatology. This coastal low will have a couple of effects; first it will help to pull the warmer moist air further north ahead of it. This means by late afternoon we could see a changeover to rain or sleet mixing in along the coast from Portland east to Penobscot bay. The existing cold air from Monday night will play a role here as a strong coastal front should be in place by the time the low could advance enough to push any warm air towards us. A narrow band of freezing rain and sleet is possible however this low will not be strong enough to push widespread warm air in aloft so any mixing will be confined to the immediate coastline. The low will move out on Tuesday night bringing precipitation to and end across all but the northern mountains. Having established the precipitation type and timing the next question becomes how much? The entire area will see around 0.5" of liquid, which corresponds to generally 4-7" of snowfall. A watch will likely be needed over much of the area. There are a few areas where amounts could differ significantly. First the downside risk, along the coast anywhere where the rain/sleet is able to mix in total snow amounts will be correspondingly lower. The upside potential is a bit tricker as there are two areas to watch. The first area would be just inland of the coastal front where the lift from the front will help to concentrate snowfall into a band with higher amounts, have tried to hint at this by increasing totals a bit in the region however this type of mesoscale feature just isn`t really predictable this far in advance. The second area to watch for upside potential would be in the trough connecting the two low centers. This region extends from approximately Brunswick to Fryeburg to Mount Washington. Wednesday - Friday: The region will hold under a cyclonic (northwesterly) flow aloft with continuing snow showers in the mountains. The low that brought Tuesdays snow will strengthen as it moves off into the maritimes providing a pressure gradient and some gusty winds on Wednesday night into Thursday. By Friday the next system is already rounding the base of the trough with more snow possible from Friday into Saturday. && .AVIATION /16Z SUNDAY THROUGH THURSDAY/... Short Term /through Monday/...VFR conditions are expected outside of the mountains today with gusty westerly winds. Areas of MVFR conditions will be possible tonight and Monday ahead of a weak low pressure system. However, most areas will see prevailing VFR conditions. Long Term...A storm will impact the region on Tuesday. Expect IFR in snow starting early Tuesday morning and continuing through the day. Snow comes to an end late Tuesday night and conditions will return to VFR by Wednesday expect in the upslope mountain areas where MVFR SHSN will persist through Thursday. && .MARINE... Short Term /through Sunday Night/...Offshore Low pressure will bring marginal SCA conditions through tonight as gusty NW/W winds develop. Long Term... A low will develop and cross the Gulf of Maine on Tuesday bringing precipitation. In its wake northwesterly flow will develop and strengthen to gale force by Wednesday night under cold advection. Gales will subside by Thursday morning but Small Craft advisories will persist through the end of the week. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...Small Craft Advisory until 6 AM EST Monday for ANZ153. Small Craft Advisory until 6 AM EST Monday for ANZ150>152-154.
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