Area Forecast Discussion
Issued by NWS Portland, ME

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875 FXUS61 KGYX 010156 AAD AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 856 PM EST Wed Nov 30 2016 .SYNOPSIS... Low pressure will track from the Great Lakes into Quebec tonight as a secondary low develops over the mid Atlantic region. This secondary low will track along the New england coast late tonight and Thursday drawing colder air into the mountains and adjacent foothills, changing a snow and rain mix there over to wet snow. Precipitation will taper off on Thursday as the low exits into the maritimes. Somewhat cooler and drier air will arrive late Thursday and Friday with temperatures cooling as we move into the weekend. && .NEAR TERM /THROUGH THURSDAY/... 853 PM Update: Based on spotter reports that corroborate GYX 88D correlation coefficient values across southern Oxford/Franklin counties...have nudged initial rain/snow line a bit further south. This lines up with about a +1C max wetbulb aloft from the RAP. Only minor adjustments in snowfall amounts were necessary. The profile in these spots is expected to warm over the next 2-3 hours...but a quick inch /2?/ of snow is not out of the question. No other changes at this time. 742 PM Update: Forecast continues to generally be in very good shape and have only made minor adjustments based on latest observations including a glance at the 00Z GYX RAOB...which shows a bit too much warm air for SN at GYX...but is well in line with near term RAP forecasts. Correlation coefficient from the GYX 88D reveals a melting layer around 4500 ft AGL...with local lowerings of this in the heavier precipitation elements. Thus...feel that ptype expectation is in good shape with no significant changes necessary. Could see some sleet mix in with the rain as far south as southern Oxford/Franklin counties...but rain will dominate even in these spots through the evening. 547 PM Update: Going forecast in good shape. Input latest observations and adjusted PoPs to slow northward progression of steadier precipitation just a tad based on latest regional radar composite. No significant changes to ptype thinking at this juncture. Will reassess after 00Z RAOB comes in over the next 1-2 hours. Previous discussion below... At 19z...a 1028 millibar high was centered over eastern Canada and was nosing southward into eastern New England. A complex area of low pressure was over the Great Lakes with a wavy frontal boundary extending through the DELMARVA region. NWS doppler radar mosaic showed an extensive area of precipitation along and to the south of the frontal system. Colder and drier air was draining south and west from northern Maine with the canadian high and will set the stage for wintry precipitation across portions of the mountains and foothills as precipitation spreads northward and the atmospheric column cools to at or below 0c. In additional...the developing coastal low will also help to draw even cooler air southward into this area late tonight and Thursday morning as it races northeast along or just offshore. There will be large variations in snow and sleet amounts as we deal with mixing as well as elevation issues. Outside of the mountains and foothills...mainly a cold rain event is expected tonight. && .SHORT TERM /THURSDAY NIGHT/... Precipitation will taper from southwest to northeast on Thursday following the passage of the coastal low and occluded front. Precipitation will linger the longest along the International border as well as eastern zones before ending during the afternoon. Some drier air will work into southern New Hampshire and southwest coastal Maine behind the departing low...with partial sunshine and westerly flow allowing temperatures to warm into the lower 50s. Highs elsewhere mainly in the 40s...with 30s across the northern mountains. Breezy and cold Thursday night with mainly clear skies for southern New Hampshire and much of the coastal plain in downslope flow. Elsewhere...cyclonic flow and upslope with a few mainly mountain snow showers. Lows will be in the 30s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... By daytime Friday cold air has already begun shifting into the Great Lakes region and New England. Additional snow showers are likely over the mountains with rain showers less likely as a surface trough moving offshore. Reinforcing cold air arrives Friday night with 850mb temperatures dropping to near -10 degrees C. Additional snow accumulations are likely Saturday on northward facing slopes as WNW winds increase aloft and at the surface. Winds will be strong and gusty from the NW on Saturday. This will help clouds clear out over the coastal plain gradually. Sunday through Tuesday cold high pressure from Canada builds in. Temperatures early in the work week will be around the mid 20s/lower 30s north to upper 30s/near 40 for highs. Overnight it looks like there will be at least a few chilly nights: Saturday, Sunday, and Monday with readings in the tens and teens across the mountains and 20s elsewhere. There will be a gradual warm up for mid week for southern NH and on the coast with warm air advection trying to nudge in ahead of the next wave arriving from the central CONUS. However...during this time cold air damming sharpens as it did earlier this week and isentropic lift increases over the cold dome at the surface. This may bring mixed precipitation and dense fog/freezing fog conditions to areas away from the coast. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... Short Term /Through Thursday night/... Summary: Low pressure will develop along an arriving front tonight and move east of the region on Thursday with another round of rain and poor flying conditions expected...with improvement by late morning Thursday and continuing through Thursday night as low pressure pulls away to the east. Restrictions: MVFR/IFR conditions will deteriorate to LIFR/IFR in rain overnight. Improvement back to VFR is expected behind departing low pressure on Thursday afternoon with VFR generally expected through Thursday night outside of some possible MVFR cigs and light snow showers at HIE. Winds: Northeasterly winds 10kts /14g22kts at the coast/ for the overnight will shift west/northwesterly during the morning Thursday and continue through the afternoon...strengthening to 10g18kts. Thursday night these winds will diminish below 10kts. LLWS: Southeasterly winds in the 1-2kft layer increase to 35-45kts for the overnight with shear ending near or just after daybreak Thursday. Long Term...RKD, AUG, and PWM will see a chance of -SHRA through mainly Friday. HIE may continue to experience -SHSN through Saturday. NW winds will be gusty especially Saturday afternoon into Sunday morning. VFR returns to all TAF sites Sunday with additional rain and snow showers moving in from the SW late Sunday into Monday. && .MARINE... Short Term /Through Thursday night/...Winds and seas build quickly ahead of the coastal low overnight and it`s likely we`ll see a period of Gales over our eastern waters including Penobscot Bay late tonight and Thursday morning immediately ahead of the coastal low. behind it...westerly flow should reach small craft. Long Term...Winds will most likely reach SCA criteria on the outer waters and bays Saturday afternoon into early Sunday. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Weather Advisory until 1 PM EST Thursday for MEZ008-013- 014. Winter Storm Warning until 3 PM EST Thursday for MEZ009. NH...None. MARINE...Small Craft Advisory until 11 AM EST Thursday for ANZ153-154. Gale Warning until 11 AM EST Thursday for ANZ150>152. && $$ SYNOPSIS... NEAR TERM...Arnott SHORT TERM... LONG TERM... AVIATION...Arnott/Hanes MARINE... is the U.S. government's official web portal to all federal, state and local government web resources and services.