Area Forecast Discussion
Issued by NWS Caribou, ME

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088 FXUS61 KCAR 240350 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 1050 PM EST Mon Jan 23 2017 .SYNOPSIS... Low pressure will intensify along the mid Atlantic coast tonight and move northeast toward the Gulf of Maine Tuesday...then across the Canadian Maritimes on Wednesday. && .NEAR TERM /THROUGH TUESDAY/... 1050 PM Update... IR Satl loop continued to show high cloudiness moving n w/enhanced clouds tops moving into extreme southern ME. Mosaic radar showed precip well back across VT & NH. Precip shield should spread into srn ME w/in the next few hrs and then spread n overnight. Hrly temps were adjusted to fit the latest trends w/some of the lower reaches dropping into the mid teens. Made an adjustment to overnight temps showing low areas across northern ME dropping to around 10 degrees. Previous Discussion... 990mb sfc low sitting off the VA/NC coast as of 19z shud begin to head up twd the NY Bight this evng in area of greatest pressure falls. Hipres along the Quebec- Newfoundland border wl build east tonight, continually supplying cold air. Clr skies wl allow temps to drop quickly tonight acrs the north bfr clds mv back in fm the southwest twd daybreak. Complicated fcst for Tuesday as coastal low mvs north along the eastern seaboard tomorrow. Wintry pcpn wl mv into coastal zones aft midnight tonight with warm nose already present btwn 850-800mb. The nwrd progression of this warm nose makes all the difference in the world regarding ptypes. 12Z GFS rmns the coldest with temps aloft while NAM rmns the warmest. Latest Euro is now the compromise and has trended twd the NAM for areas along the Maine/NB border. Given the juxtaposition of the sfc high to the north with erly flow at the sfc, thinking is that blyr wl lkly be below freezing thru Wed mrng. Question bcms what flow aloft arnd H8 does. 12z NAM indicates srly 55-60kt H8 LLJ on Tue straight off the Atlantic, whereas GFS and EC indicate a more erly jet, thus not as much of a warm nose. For wx grids hv blended the 12z NAM and 00z EC therefore expecting mostly a sleet storm for the bulk of the precip duration. Thorough investigation of NAM/GFS BUFKIT sndgs for the area hinge on how warm the warm nose becomes and how thick the warm and cold lyrs are and which model has the best handle on atmos. A difference of a few hundred feet as well as 1C will make all the difference in the world in regard to ptype. Have opted to issue a Winter Storm Warning for areas north of a Dover-Foxcroft to Oxbow line for several inches of snow, a few inches of sleet as well as a glaze of ice. For areas further to the south, specifically along an Ellsworth to Princeton line, think that sleet wl eventually change over to a possibly prolonged time of freezing rain. Cannot rule out up to one- half inch of ice especially in the Grand Lakes to Vanceboro region, though aforementioned uncertainties could lead to more sleet and less ice. Therefore hv issued a Winter Storm Warning for Interior Downeast and the Bangor area due to a combo of sleet and ice. Along the coast, hv gone with a Winter Weather Advisory for minor sleet accums along with a glaze of ice tomorrow morning. Warm air shud surge along the coast and allow these areas to rise abv freezing shortly after noon, ending the threat. Easterly winds wl gust to between 40 and 45kts as pressure gradient tightens btwn sfc low to the south and hipres to the north. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... For Tuesday night, a significant sleet and freezing rain event will continue. A vertically stacked low will slowly progress northward towards the Gulf of Maine by later in the night. The low will draw a rich flow of Atlantic moisture northward into the forecast area through the night into Wednesday morning. PWATs are several standard deviations above normal and there`s some instability aloft. The moisture will not move through the area quickly due to a blocking high in Labrador. There`s not much cold air aloft and a southerly flow aloft is expected to bring temperatures in a layer above H850 well above freezing. Therefore, snow is not an issue...except perhaps in extreme NW Aroostook County., However, in a narrow wedge under H850, a cold easterly flow will prevail north of the low. The cold air under H850 means rain will refreeze as sleet or freezing rain for most of the area. The big challenges in the forecast were where to place the 32F line at the surface through the night and the strength of the elevated warm layer. The 23/12Z NAM suggested a more southerly flow aloft and greater warming aloft versus the colder GFS. In the end, the NAM was blended with the ECMWF to produce a swatch of freezing rain from southern Penobscot County towards north-central Washington County and southern Aroostook County. This area has the potential to receive anywhere from a half to three-quarters of an inch of freezing rain. Along the coast, precipitation will be rain and winds will die down in the evening. For the northern zones, the cold layer looks just deep enough for sleet through the night and sleet may be measured in inches. If temperatures aloft are just a bit warmer, significant freezing rain accumulations will have to be pushed northward. For Wednesday, the storm will be over for most of the area except lingering mixed precip in NE Aroostook County for the morning. After the precipitation moves out, the frontal inversion will erode and temperatures will rise above freezing. Winds be generally light...which is good news in light of any ice accumulations. A lot of cloud cover will remain Wednesday into Wednesday night as low level moisture remains. There`s no significant cold air advection behind this system as lows on Wednesday night will drop just below freezing...which could cause some slick spots. The colder air arrives after a clipper system on Thursday. This system will produce light precip amounts with up to an inch of snow in the northern half of the forecast area. Meanwhile, with temperatures in the mid to upper 30s, Bangor and the Down East region will have rain shower activity. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... The long term pattern features a return towards more seasonable temperatures, but no particularly cold air masses. With a broad upper trough over the NE US, it will be generally dry and free of any significant storms. Weaker clipper systems may rotate from the Great Lakes, but exact timing of resulting snow shower activity cannot be readily discerned at this point. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/... NEAR TERM: VFR tonight becoming IFR after 10z at BHB and BGR in mixed precipitation. HUL may see IFR between 15z and 18z in -SNPL though confidence was not high and have just included mixed precip in tempo group. SHORT TERM: Hazardous aviation conditions are expected Tuesday night with LLWS and freezing rain/sleet. This will also be accompanied by low IFR cigs. The low IFR cigs will continue north of HUL into Thursday...and gradually improve to a prevailing MVFR condition Thursday night into Friday. Snow showers could reduce vis for sites north of GNR and MLT on Thursday afternoon. && .MARINE... NEAR TERM: SCA conditions continue this evening before increasing to gales for the intracoastal area after 10z and storms on the outer waters. By Tue afternoon expect headlines wl need to be replaced with another SCA after this time. Expect seas to be increase aoa 15ft on Tue. SHORT TERM: After the storm ends, a small craft advisory will be needed into Wednesday afternoon. After a small respite, the next small craft advisory seems destined to run from later Thursday morning into Saturday night. && .TIDES/COASTAL FLOODING... A storm surge of up to 1.5 feet is expected along with large waves. The astronomical high tide will occur shortly after 8 am Tuesday morning, however the largest waves are not expected to arrive until later in the morning. As a result only minor splash over is expected. Astronomical tides are also relatively low, so coastal flooding is not expected. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...Winter Storm Warning from 7 AM Tuesday to 1 PM EST Wednesday for MEZ001>006-010-011-015>017-031-032. Winter Weather Advisory until 1 PM EST Tuesday for MEZ029-030. Wind Advisory from 4 AM to 7 PM EST Tuesday for MEZ029-030. MARINE...Gale Warning from 5 AM to 1 PM EST Tuesday for ANZ052. Small Craft Advisory until 5 AM EST Tuesday for ANZ050-051. Storm Warning from 5 AM to 1 PM EST Tuesday for ANZ050-051. && $$ Near Term...Hewitt

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