Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 120024 AFDGYX Area Forecast Discussion National Weather Service Gray ME 724 PM EST Mon Dec 11 2017 .SYNOPSIS... After a cold night tonight, low pressure will move toward New England from the west on Tuesday. This will spread snow across the area to start the day, changing to rain along the coastal plain. Low pressure moves off to the northeast Tuesday night and an Arctic cold front pushes east across the region early on Wednesday. This will put northern New England in the deep freeze as the temperature will likely stay below freezing into the weekend. The next significant low pressure system is expected to track off the New England coast Sunday night into Monday, bringing another chance of snow. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Update... Quick update to tweak temperatures, dew points and the near term wind forecast. A cold front has crossed the region, allowing for temperatures to drop rather quickly in the mountains. Have lowered readings in the mountains by several degrees based on current observations and trends. Thereafter, clouds increase and thicken, slowing any radiational cooling. Prev Disc... For tonight, temperatures will drop into the single digits to lower teens north with upper teens and lower 20s south. Increasing cloud cover moves in rapidly tonight. High pressure gradually shifts away as low pressure approaches from the west. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Main Concerns... **Heavy Snow expected for much of the area by rush hour Tuesday morning and continuing into the Tuesday afternoon rush hour*** **An Arctic air mass ushers in much colder air by Tuesday night*** A dynamic weather system now moving into the western Great Lakes will be approaching the region very late tonight. Low pressure at the surface will deepen and reorganize over the NH/ME border with models agreeing on a 989MB low deepening to near 984MB by late tomorrow evening. Confidence is high that this storm will produce heavy snow for much of the foothills and mountains. However, as the storm deepens, a coastal front will draw warmer air north changing snow quickly over to rain for the coast and portions of inland NH and ME. Thus mesoscale nuances will make or break forecasted snowfall amounts. The coast and areas just inland may see mostly rain from this event. Farther inland...including interior southern NH and Maine, we will see closer to 3-6" of snow with colder temperatures in place. Even farther north there will be a sharp uptick in snowfall amounts where colder air is currently (and will still be) dammed north of the higher terrain. In this area expect widespread 8-12" inches. Watches have been converted to warnings and advisories accordingly. Other concerns with this forecast include temperatures falling across much of NH and northern ME Tuesday night into the teens by daybreak as the Arctic front sweeps eastward with time. Depending on the timing and how fast this occurs, a flash freeze may be a concern for areas that receive rain. Winds will be gusty tomorrow night with the system wrapping up and lifting NNE as a dry slot works in from the SW. Additional snow is likely for the mountains as it lifts out. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... A strong cold front pushes east across the area on Wednesday. High temperatures will likely be around sunrise with temperatures falling sharply behind the front. With cold advection and deep mixing, winds will be gusty as well, with gusts to 30 MPH likely and 40 MPH possible. This will make it feel even colder, with wind chill values dropping below zero by Wednesday evening into Wednesday night. A shortwave trough tracks quickly east well to the south of New England on Thursday, far enough south to avoid any impacts in our area. Temperatures will be cold, generally in the 20s for highs. High pressure builds in for Thursday night bringing decent radiational cooling conditions, so expect lows in the single digits above and below zero. The next trough moves by on Friday/Friday night. The GFS would have us believe that this will cause a surface low to track close enough to bring snow to the coast, but it appears to be the outlier among the models and within its own ensembles. Therefore will not put too much weight into that solution and keep the forecast mostly dry. In the wake of the Friday night trough, models are rather inconsistent on the details of the various waves within the westerly flow. It is possible that a wave could move by Saturday or Sunday but it won`t have much moisture with it so if precipitation does occur it would only produce light snow. The next more substantial wave moves up the northeast US coast Sunday night into Monday. This track would put our area in the sweet spot for another round of snowfall. The GFS is a littler further east with the track, so it is colder and a bit drier, while the ECMWF brings heavier precipitation and a low track close enough to the coast to think about a rain/snow line. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Short Term...Expect conditions to rapidly deteriorate to IFR early Tuesday morning generally from west to east with periods of LIFR in heavy snow expected for New Hampshire between 12Z and 20Z and into central and northern Maine from 15Z-00Z. Long Term...Conditions should go to VFR behind a cold front on Wednesday, with the exception of the northern mountains where MVFR/IFR ceilings and light snow may continue. Winds on Wednesday will gust up to 30KT behind the front. Mostly VFR conditions expected into the weekend. && .MARINE... Short Term...Have discontinued the SCA for this evening in favor of issuing gale warnings for all marine zones beginning Tuesday morning as a strong low pressure system moves through. Long Term...A cold front crosses the waters early Wednesday with winds gusting to 40KT or so behind it. Westerly flow may not fall below advisory levels until Thursday night as high pressure builds in. Low pressure will track northeast through the western Atlantic on Friday night into Saturday, and it could come close enough to provide stronger north to northeast winds for a time. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Warning from 4 AM Tuesday to 1 AM EST Wednesday for MEZ007>009-012>014. Winter Weather Advisory from 4 AM Tuesday to 1 AM EST Wednesday for MEZ018>022. NH...Winter Storm Warning from 2 AM Tuesday to 1 AM EST Wednesday for NHZ001>006. Winter Weather Advisory from 2 AM Tuesday to 1 AM EST Wednesday for NHZ007>011-015. MARINE...Gale Warning from 10 AM Tuesday to 1 AM EST Wednesday for ANZ150>154. && $$ JC is the U.S. government's official web portal to all federal, state and local government web resources and services.