Area Forecast Discussion
Issued by NWS Portland, ME

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681 FXUS61 KGYX 102331 AFDGYX Area Forecast Discussion National Weather Service Gray ME 631 PM EST Sat Dec 10 2016 .SYNOPSIS... High pressure moves into the area tonight providing a mostly clear sky, light winds, and very cold temperatures. High pressure will move east on Sunday with continued cold temperatures over New England. Low pressure moving through the Great Lakes Sunday night into Monday will spread snowfall into northern New England as it shifts toward the Gulf of Maine. There may be some areas along the coast which mix with rain before precipitation ends Monday afternoon. High pressure builds in behind the system for Tuesday. A series of cold fronts Wednesday and Thursday will bring progressively colder temperatures into the area. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Update... Have updated the grids based on current observations. Snow showers continue to diminish in the mountains, however clouds are hanging tough in the north. This is keeping temperatures in the mid teens across the high terrain. Further south, with clear skies and light winds temperatures are beginning to take a nosedive. May need to adjust readings downwards over southern areas by a couple degrees. Otherwise, just minor modifications were completed with cloud cover and dew points for this package update. Prev Disc... High pressure will nose its way into the area tonight, providing calm winds and pretty good radiational cooling conditions for most of the area. Still some uncertainty on whether clouds will dissipate in the mountains or not. Clouds have hung on tough there all day with temperatures holding steady. Upstream areas have seen an abundance of cumulus clouds developing this afternoon, and this low level moisture may remain locked in the upslope areas through the evening. But with high pressure moving in, expect advection to cease and clouds could dissipate. If they do, temperatures could fall to near zero in the northern valleys, but if the clouds hang on then temperatures may stay in the teens. Elsewhere, it should be a fairly good radiational cooling night with most areas falling into the single digits. On Sunday high pressure shifts east and temperatures should warm a few degrees. Still looking at highs below freezing, but a few degrees warmer than they were today. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... A low will develop across the Great Lakes and move across northern New England bringing widespread snow from Sunday evening into Monday. Overrunning precipitation ahead of the warm front will move into southern New Hampshire late Sunday night and spread across the entire region by daybreak. The cold high pressure from the weekend will keep cold air lingering at the surface setting up cold air damming. Even global scale models show hints of the high pressure ridge and easterly surface flow along the interior of Maine signaling the cold air dome. This cold air will be key to the precipitation type. As the low center moves across the area the warm sector aloft pushes northwards. The warmest option... the NAM allows temperatures to reach +3C along the Maine coast.. while the colder options keep temps below 0C through the entire column. Have leaned towards the colder solution with just a minor warm air intrusion and temps aloft reaching around +1C. The warmer solution is quite aggressive but at the same time the colder solutions have been trending warmer over the past few runs. A comfortable mid ground keeps just a bit of mixing along the coast with a brief region of sleet as the warm air aloft moves in during the day on Monday. Through the interior the cold air aloft as well as the surface cold dome keeps ptype all snow. As the low pressure moves through the area Monday afternoon the precipitation will come to an abrupt end as the dry slot moves in. A brief period of drizzle across the south and freezing drizzle in the interior and mountains is expected before the entire atmosphere dries out. The cold air dome will also result in a surface coastal front... expected to remain along I-95 in southern Maine and NH and extending northeastward through RKD. Solid 20kt winds on the ocean side of the front will help to maximize lift over the cold dome and increase precipitation just inland. Have increased QPF amounts a bit just inland of this line to account for this. && .LONG TERM /TUESDAY THROUGH SATURDAY/... The coldest air so far this season is expected over northern New England as temperatures at 850mb bottom out near -30 C over NH and ME in the mid week timeframe. Deterministic and ensemble means are in good agreement concerning the cutoff low moving into Ontario on Monday night into Tuesday morning....shifting into Quebec province by Thursday morning. This particular upper low swings over the northern Great Lakes and northern New England and towards Greenland by the end of the week. As mentioned the main story with this system will be the extreme cold which sets in as early as Wednesday night and trends colder each day through Friday as reinforcing cold and dry air funnels in from the north in a couple different waves. In more detail, temperatures over the mountains will drop to single digits Wednesday night, decreasing with each successive night through Friday night until some locations reach as low as -15 degrees F. In the daytime hours northern sections will struggle to make it above single digits for highs. Farther south...inland and coastal sections will drop only reach the teens and 20s during the day. We will most likely need to issue a wind chill advisory behind a departing baroclinic zone associated with ejecting Atlantic low pressure Thursday night into Friday morning. Would not be surprised if other periods met wind chill advisory criteria as well. During this time mean cyclonic flow as well as upslope forcing will bring periods of snow showers...especially for the higher terrain. With extremely cold and dry air in place most snow will be of the fluffy variety. The only places we may see rain would be offshore early on, on the south side of the coastal front. Ridging aloft arrives for next weekend. Another quick moving frontal system affects the northeast during this time. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... Short Term...VFR conditions expected through tonight. Conditions will rapidly deteriorate to IFR snow from west to east on Sunday night and remain IFR through Tuesday. Wind shear will impact all terminals on Monday as a LLJ of around 50kts moves through with the low center. Long Term...Periods of IFR/MVFR in snow showers are likely for HIE and perhaps LEB Wednesday. Widespread snow showers are expected Thursday bringing ceilings and visibilities down to LIFR/IFR. Surface winds Thursday into Friday morning will gust into the 25-30 kt range. && .MARINE... Short Term...Offshore winds gusting to around 25 KT will continue into the evening before dissipating. Should see a window from Sunday into Sunday night of fairly quiet conditions on the waters before the approaching low tracks near the Gulf of Maine on Monday. This should bring winds back up to near Small Craft Criteria levels for the waters. Long Term...Small craft advisory for winds may be needed Wednesday into Thursday as low pressure passes SE of the waters. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Watch from late Sunday night through Monday evening for MEZ012>014-018>028. NH...Winter Storm Watch from late Sunday night through Monday evening for NHZ004-006-008>010-014. Winter Storm Watch from Sunday evening through Monday evening for NHZ007-011>013-015. MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ150- 152-154. && $$ JC

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