Area Forecast Discussion
Issued by NWS Caribou, ME

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000 FXUS61 KCAR 121120 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 620 AM EST Tue Dec 12 2017 .SYNOPSIS... Low pressure across the eastern Great Lakes will deepen today and tonight and track across Maine tonight into Wednesday morning and will pull away to the north of the region Wednesday afternoon. High pressure will build to the south of the area Friday. && .NEAR TERM /THROUGH WEDNESDAY/...
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6:20 am update: Snow is spreading into southern Maine and to the Mid Coast as of 6 am. The snow will develop over the next few hours across much of the Central Highlands, Bangor Region, and Downeast. The snow is still expected to reach the Saint John Valley by around noon. Only minor tweaks to the forecast based on the latest observations, but the start time of the snow still looks to be on track. Previous discussion... Low pressure with multiple centers across the eastern Great Lakes south to western PA early this morning will track into NY State today and to near Portland, Maine by 00z this evening. The low is expected to deepen tonight and track into northern Maine by Wednesday morning, and then gradually pull away to the north during the day. Snow will rapidly overspread the area today, starting first in southwest Piscatquis County by 8 or 9 am, and reaching far northeast Maine and the eastern Saint John Valley by around noon. A strong onshore flow and ocean temperatures in the upper 40s will allow the snow to rapidly change to rain after an hour or two along the immediate coast with any accumulation an inch or less. In the Greater Bangor Region, expect a period of snow for several hours with the snow to change to rain by late afternoon or early evening after a few inches of snow. The warm surge works rapidly to the north during the night, and by 09-12z the snow may mix with or change to rain all the way north to Caribou as there is layer above freezing between 800-900H. Temperatures at the surface will likely be below freezing, so there could be a bit of freezing rain; however, it is unlikely to be a major issue after several inches of snow. Most of the significant precipitation lifts out of far northern Maine Wednesday morning with the deformation zone to generally set up along or just west of western Maine/Quebec border. Colder air sweeps back into the area from the southwest during the day. Current thoughts are that the snowfall totals look very good across the Downeast area, but are likely a bit high in the north and will trim them back a bit. Also, will end the last of the warnings by 21Z Wednesday and not have them extend into Wed night with this update. There will also be a fairly strong jet along the coast later this afternoon into this evening with gusts to 45 mph possible, and will issue a wind advisory for late this afternoon into this evening for coastal Hancock and coastal Washington Counties.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/... The model guidance is in good agreement through the short term period of the forecast. An upper level low will be moving across northern Maine at the start of the period, an associated surface low will be centered near the mouth of the St Lawrence. Wrap around precipitation will extend into northern Maine. Thursday morning the upper low will regress north over central Quebec, a weak ridge of higher pressure will build into Maine as another low move into the north Atlantic along the NJ coast. This low will track across the Gulf of Maine through the end of the period bringing a chance for some snowshowers to Downeast Maine Thursday. Loaded a blend of the GFS/NAM/ECMWF to smooth out the minor differences in the models. Loaded NAWAVE4 for seas in the coastal waters. Loaded windgust by factor tool. For QPF used GFS. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... The extended models are in good general agreement at the start of the period. An active weather pattern will continue through the extended period as an upper low over Northern Canada will spin off troughs and clipper system about 12 to 18 hrs apart through the period. At this time most appear to only support 1 to around 3 inches of snow. Loaded a blend to smooth out the differences in the models, however the solution leans more towards the GFS solution. Used NAWAVE4 for seas in the coastal waters. Used windgust by factor tool. && .AVIATION /11Z TUESDAY THROUGH SATURDAY/... NEAR TERM: Conditions will lower to LIFR at Downeast terminals by late morning, and by early to mid afternoon at the northern terminals. LIFR will improve to MVFR late tonight at the Downeast terminals, and during the day Wednesday at the northern terminals; although IFR and LIFR still possible at times in snow showers. SHORT TERM: MVFR conditions across northern Maine with scattered snowshowers. VFR conditions for Southeastern Maine today. High pressure builds into the area this afternoon bring clearing conditions. MVFR condition will remain across northern Maine as an upper level low over central Quebec bring wrap around snowshowers to northern Maine. These conditions will continue unto Friday morning when the upper low begins to move NE toward the Maritimes and higher pressure builds across the whole state. Condition will fall to IFR from south to north on Saturday morning as a low and associated frontal system moves into the state. IFR condition will remain through the end of the period. && .MARINE... NEAR TERM: A gale warning is in effect from 3 pm this afternoon until midnight tonight. Conditons will lower to SCA overnight, but another period of gales is likely Wednesday. SHORT TERM: A Gale Warning may be required through much of the period as a low pressure system moves through the Gulf of Maine waters. && .CLIMATE... The low yesterday at Caribou of -8F was the first sub-zero temperature of the season. The average date of the first sub-zero temperature at Caribou is December 12th. && .CAR WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Storm Warning from 11 AM this morning to 1 PM EST Wednesday for MEZ002. Winter Storm Warning until 7 PM EST Wednesday for MEZ001-003- 004-010. Winter Weather Advisory until 5 AM EST Wednesday for MEZ005- 006-011-031-032. Winter Weather Advisory until 7 PM EST this evening for MEZ015>017. Wind Advisory from 4 PM this afternoon to 11 PM EST this evening for MEZ029-030. MARINE...Gale Warning from 3 PM this afternoon to midnight EST tonight for ANZ050>052.
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