Area Forecast Discussion
Issued by NWS Caribou, ME

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000 FXUS61 KCAR 200248 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 1048 PM EDT Mon Mar 19 2018 .SYNOPSIS... High pressure will continue to build down from the northwest overnight. Low pressure will develop off the Mid- Atlantic coast on Tuesday. The low will track to a position off southern New England on Wednesday then south of Nova Scotia on Thursday. && .NEAR TERM /THROUGH TUESDAY/...
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1047 PM Update... Light snow/flurries have ended w/the latest IR satl imagery showing clouds breaking up. This is being backed up by the latest LAPS soundings showing the llvls drying out. NW winds have stayed up 10-15 mph sustained w/gusts to 25 mph. The winds are expected to remain up overnight. Some partial clearing expected overnight. Temps have stayed up this evening due to the winds. Slight adjustments were made to bring the overnight mins up a few degrees. Otherwise, no other changes. Previous Discussion... High pressure continues to build down from central Canada as low pressure both surface and aloft remains well to our northeast. Some moisture wrapping south from the low will bring patchy stratocumulus clouds across the north overnight and some flurries may be around this evening. Otherwise, dry and cold and continued breezy. A corridor of dry air will run southeast from the high across Downeast areas on Tuesday while some moisture continues to back south from Canada across the north. This will bring variable cloudiness over the north while Downeast is mostly sunny on Tuesday. Afternoon highs will be a bit higher than Monday`s highs but still around 5 degrees below normal for the first day of spring.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... On Tuesday night, the surface high centered over James Bay will remain in control with a ridge line extending into Maine. The deep low level cold air will remain entrenched and the primary question will be whether a subsidence inversion will hold stratocumulus or if radiational cooling will produce lows below guidance. For now, will go just below under guidance rather than betting big as northwesterly flow reduces confidence in clear skies and calm winds all night. The high remains in control Wednesday with a strengthening NE flow resulting from a tightening pressure gradient between the James Bay high and a deepening surface low off the Delmarva peninsula. This means both increasing stratocumulus advecting from the east and high clouds thickening later in the day as moisture above H500 increases. Have leaned towards GFS H850 moisture fields for Wednesday`s cloud forecast. Things become more interesting Wednesday night. The vertically stacked low off the Delmarva coast will send an its wraparound occlusion towards the coast...accompanied by a shortwave rotating around the closed upper low. At the same time, the entire closed upper low will drift northward towards eastern Maine or Nova Scotia Wednesday night into Thursday as northern and southern streams phase. This time, there`s no blocking upper high to prevent the upper low from drifting northward. While the occlusion will be weakening and the surface low will be well offshore, moisture wrapped around the upper low in the trowal could affect the forecast area for much of Thursday. This will be an all-snow event, with the possible exception of some sleet towards Eastport due to warm air aloft in the occlusion. Ultimately, snowfall amounts and duration will be based on the exact track of the upper low, but certainly the current trend is pushing the upper low closer to Maine. Since we`re dealing with closed upper lows, prefer using ensemble means rather any particular deterministic model. Also of note is a strong northeasterly H900 jet coinciding with occlusion and potential for some elevated instability. This could generate some heavier snowfall towards the coast on Wednesday night if it materializes. The Down East region stands the best chance of advisory or warning level snowfalls from this system and the Allagash would likely receive the least as amounts taper to the NW. The LLJ will help create surface wind gusts over 30 mph...and possibly up to 40 mph Wednesday night into Thursday. Thus blowing snow will be a threat. Have not entered that into the forecast yet, but it should go into the forecast as confidence grows in this event. Furthermore, the winds could generate a storm surge along the coast that could cause some minor coastal flooding. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Thursday night into Friday, guidance is in decent agreement with regard to the upper low pulling away into the Canadian Maritimes, weak ridging over the area and a north to northwest flow. This probably means a lot of cu and stratocu and a few flurries. Things become more confused Saturday into Sunday as an omega block is established over eastern/central Canada. Maine will be on the right side of the block and the confusion lies in exactly where the closed low will set up. GFS has the upper low over the area with a chance of snow showers though the weekend. Previous runs of the ECMWF and GEMS put the closed low further north and located Maine nearer to a shortwave rotating on the south side of the closed low. However, with today`s 12Z guidance, the ECMWF and GEMS have fallen in line with the GFS. The high pressure part of the omega increases influence on the area Monday into Tuesday next week. This promises to bring some much warmer temperatures with highs returning to the 40s. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... NEAR TERM: VFR conditions are expected across the area today and tonight. SHORT TERM: All sites will be VFR Tuesday night and Wednesday. IFR conditions...tempo LIFR...will hit the coast on Wednesday evening and spread north overnight and continue Thursday. The snow will be accompanied by strong NE winds gusting over 30 mph and possible LLWS with up to 50kt of wind near 3000 ft. Conditions will lift to MVFR later Thursday into Thursday night. In general, expect mostly MVFR cigs north of HUL later Thursday into Sunday while VFR conditions are expected towards BGR and BHB. && .MARINE... NEAR TERM: A SCA will continue into mid morning Tuesday. Winds should then finally drop below SCA from late morning into Tuesday afternoon as high pressure crests over the waters. SHORT TERM: A Gale Warning seems like a strong bet for Wednesday afternoon into Thursday morning...tapering to an SCA Thursday morning into Thursday night. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...Small Craft Advisory until 10 AM EDT Tuesday for ANZ050>052. && $$ Near Term...Hewitt is the U.S. government's official web portal to all federal, state and local government web resources and services.