Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 180515 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1215 AM EST Wed Jan 18 2017 .SYNOPSIS... Low pressure will move east from the Great Lakes overnight, then redevelop off the mid Atlantic coast by early Wednesday. This system will bring widespread snow, with highest amounts in the south and some mixed precipitation along the coast. Another weak front will pass through the area early Thursday. This will be mainly dry with just clouds across the region and a few upslope snow showers along the Canadian border. High pressure will build in for the remainder of the week, with above normal temperatures expected into Monday. A storm system may affect the region Tuesday and Wednesday. && .NEAR TERM /UNTIL 9 AM THIS MORNING/...
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midnight update... Adjusted snowfall to reflect current reports. Southern NH has seen around 2-3 inches with western Merrimack around 4. Further east the snow has yet to move in and so that results in a slightly lower total than the last update. Pressure falls continue to be around 3mb just southeast of long island as the low develops. Best dynamics will be for the next few hours as the low intensifies. The low will move east a bit too rapidly for the northern portion of the CWA and I expect snow totals may be lower across that area. With no snow observations and the strongest period of precipitation yet to develop have held off on any major changes. 920 PM...Precipitation shield continues to spread north and east across the forecast area at moment ahead of the 1009 millibar low over Lake Ontario. Three hour pressure falls are centered southeast of New York City and I expect the secondary low to develop in this area over the few hours. Current forecast is in decent shape and for this ESTF update I ingested the current mesonet and made minor adjustments to sky grids to reflect satellite trend. Prev Disc... Overall, not much change to the previous forecast. 12z forecast models and latest ensemble data are in pretty good agreement with forcing for ascent and subsequent QPF and dendritic growth. The result was a high-end advisory to low-end warning snow event starting this evening, with the heaviest snowfall later this evening into the early overnight hours. Most areas will fall into the 4 to 7 inch range with locally higher amounts possible in the warning area. Snowfall rates this evening may exceed 1" per hour, particularly across southern and central NH as a band of strong waa/frontogenetical forcing moves through...with the resultant omega co-located with the dendritic growth zone. This signal weakens as it enters Maine, and therefore snowfall rates are expected to be less intense there, with final totals lower as well. In addition, the boundary layer will be close to or above freezing at the onset of the precipitation in many coastal and central/southern zones. This may allow the precipitation to begin as rain and possibly even some sleet in some areas. However, as dynamics take over, a change to snow is imminent an hour or two after onset. The will be a few hours either side of midnight before tapering off late. Overall, the period of heavy snowfall is expected to be relatively brief. The main uncertainty in snow amounts is along the seacoast of NH and the immediate coast of Maine where an onshore flow will prolong any mixing with rainfall. However, with in-situ cold air damming developing overnight, snow may be the predominant type even there. Therefore, advisories remain in effect. Some uncertainty also exists in amounts close to the MA border as some sleet may mix in which could keep snow amounts down some.
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&& .SHORT TERM /9 AM THIS MORNING THROUGH 6 PM THURSDAY/... The heaviest snowfall should be over with by 6 am Wednesday. Much of the day will feature cool, cloudy northeast flow with occasional light snow. The mid levels dry out later in the morning and afternoon. However, with the low level remaining moist, some light freezing drizzle and drizzle is possible. A short wave trough will once again approach Wednesday night and may once again bring a period of light snow or snow showers to the region, especially north. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Fairly quiet weather is expected through most of the long term period with unsettled weather early next week. The overall weather pattern will be changing very slowly during the long term period. The main features will be weak northwest flow as an upper level trough remains just east of the region...with several areas of high pressure dropping southeastward from central Canada. At the same time, an area of low pressure over the central U.S. will try to move northeastward toward the surface ridge. As a result, any moisture from the low will be slow to move into the area with the possibility of mixed precipitation early next week. More specifically, a trough will pass through the region early Thursday and could bring some snow showers to the region Thursday morning. The trough will move east during the day Thursday allowing some partly cloudy skies across southern areas Thursday afternoon. In the mountains, cloudy skies and scattered snow showers will persist into the evening. As the trough moves slowly east Friday through Sunday, a ridge of high pressure will build southeastward from central Canada. As the high moves off the coast late Monday and Tuesday, a southeast flow will start to develop across the area ahead of the approaching area of low pressure. This will allow temps to warm aloft...but models continue to show some surface cold air damming across the region. At this time, it looks like we`ll see mixed precipitation across the region Monday night into Tuesday...with precipitation gradually changing to rain during the day Tuesday across southern areas. However, there remains much uncertainty in the progression of these systems, so there is low confidence in the details of the forecast for early next week. Models are generally in agreement on overall pattern, although details vary a bit. && .AVIATION /05Z WEDNESDAY THROUGH SUNDAY/... Short Term...VFR conditions will deteriorate to MVFR then IFR in many areas this evening and overnight in snow. Precipitation intensity will lighten after 09z tonight but low clouds, light snow, and some drizzle should keep conditions predominantly IFR through Wed and possibly Wed night. Long Term...MVFR conditions expected Thursday morning improving to VFR late in the day except in the mountains where mvfr conditions may persist into Friday. Mainly VFR conditions expected through the weekend. && .MARINE... Short Term...SCA in effect as storm system moves to our south tonight through Wednesday and allows for building seas and stiffening northeasterly flow. Long Term...SCA criteria (for seas) possible Thursday. Winds and seas should be below SCA criteria Thursday night through Sunday. Increasing southeasterly flow will allow seas to build early next week. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Storm Warning until 5 PM EST this afternoon for MEZ012- 018>020. Winter Weather Advisory until 5 PM EST this afternoon for MEZ013-021-023>026. NH...Winter Storm Warning until 5 PM EST this afternoon for NHZ004- 006-008>010-015. Winter Weather Advisory until 5 PM EST this afternoon for NHZ002-003-005-007-011>014. MARINE...Small Craft Advisory from 7 AM this morning to midnight EST tonight for ANZ153. Small Craft Advisory until midnight EST tonight for ANZ150>152- 154.
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&& $$ SYNOPSIS... NEAR TERM...Curtis SHORT TERM...Ekster LONG TERM...Jensenius AVIATION...Ekster/Jensenius MARINE...Ekster/Jensenius

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