Area Forecast Discussion
Issued by NWS Caribou, ME

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000 FXUS61 KCAR 200132 AAB AFDCAR Area Forecast Discussion...UPDATED National Weather Service Caribou ME 932 PM EDT Wed Apr 19 2017 .SYNOPSIS... A cold front will pass through state late tonight into Thursday. Weak high pressure will build later Thursday. Another low pressure will approach from the Great Lakes region on Friday. && .NEAR TERM /THROUGH THURSDAY/...
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930pm Update: Made some changes to cut back on categorical/likely pops about 3 hours quicker based on current radar/satellite trends. Precipitation type and temperatures are working out well, the overall moderate snowfall will just be ending a few hours earlier than anticipated, snow showers will linger into tomorrow morning though as the upper level vort max swings through. 7pm Update: Forecast is on track with snow being reported across the Central Highlands at this time and Millinocket ASOS is reporting a rain/snow mix. Just made a few small adjustments to speed up the transistion to snow in some areas by dropping surface temps a few degrees. Still looks like a slushy few inches for Northern Maine tonight. Will have to watch road impacts as Monson MDOT station road temp has already dropped to 31 degrees. Well, tdys 12z opnl model suite indicated a little more in way of BL-850mb sub-fzg/dry air ovr Nrn and E cntrl ptns of the region later this eve into the erly morn hrs Thu with the precip band ahead of a weak cold/occluded front from QB. This air alf is cold and dry enough to chg any onset of rn erly this eve to all wet sn within 1 to 2 hrs aftwrds by late eve. In fact, far Wrn ptns of the region, including Nrn Somerset county, may experience chgovr back to all rn late tngt due to llvl warm air advcg NE from the St Lawrence Vly; but this llvl warm air will not arrive in time across the NE before the precip tapers off to shwrs Thu morn. Total sn accumulations, which now will be partly trrn driven and perhaps more dynamically driven will msly range from 1 to 3 inches across the NE hlf of the FA, this based on some of half inch total QPF being intially used up with rn onset and erly melting of initial snfl, and keeping max sn to liq ratios to no more than 8 to 1. The very high trrn abv 2000ft MSL of Baxter St Park and the Cntrl ME Highlands could receive up to 3 to 5 inches. Given the limitations of warm grnd sfcs and relatively low sn to liq ratios, our current snfl fcst is between the 25 to 50 percentile of all ensmbl snfl fcsts...with higher 75th to 90th percentile ensmbl fcsts suggesting the potential of 3 to 5 inch sn adv amts ovr the far NE, an unlikely but still possible outcome if snfl rates become heavy enough. Otherwise, organized snfl should end as sct rn-sn shwrs across the NE and E Cntrl ptns of the Rgn by late Thu morn with breaks in the ovc across the region by mid to late aftn. With little in the way of cold air behind this front, hi temps should recover well int the 40s at most lctns Thu aftn and even lower 50s across the lower Penobscot vly. Aft a brief pd of mclr to ptly cld skies Thu eve...cldnss will return later Thu ngt ahead of the next low apchg from the Great Lks, with lgt mixed precip onset already invading wrn ptns of the region erly Fri morn. Most lctns will experience earlier pre-sunrise ovrngt lows due to the advc of thicker cld W to E across the Rgn cvr late Thu ngt.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... On Friday, weak high pressure will be pulling away. A low level flow with a southerly component will provide warming to the boundary layer as well as some upslope drizzle, fog and low clouds in the morning. As the day progresses, a slow-moving vertically stacked low in eastern Ontario will meander eastward and rain will break out across the area with increasing pops through the day. After highs in the the 40s, a number of factors will cool the column as the evening approaches. As the upper low drifts into Quebec, the parent surface low will fill and a new coastal low will emerge off the New Jersey coast. At this point, warm advection will cease and cooler low level air will advect into northern zones. Evaporative cooling will also wipe out boundary layer warmth. Cooling aloft will also occur as the upper low approaches. The net result will be a changeover to snow during Friday evening...mostly north of a line from Greenville towards Houlton. North of this line, one to two inches of snow could fall. The changeover...and duration of snow will occur earliest towards the western mountains and the Crown of Maine. At this point, a worst case scenario for higher terrain in northern Aroostook County could be 2 to 3 inches by Saturday morning. Further south towards Bangor and Ellsworth, precipitation will remain mostly rain all night. In general, precipitation does look to be sufficient to cause any hydro issues with rivers already swollen with snowmelt. Total QPF for most areas should be just over a half inch or less. Lows on Friday night will drop to the lower 30s north and mid 30s in the southern half of the forecast area. Snow will end in northern zones on Saturday morning as the upper trough slowly crosses and the coastal low pulls away from the Gulf of Maine. With a northeast surface flow, skies will remain cloudy through Saturday and limit highs to the low 40s north and upper 40s for Bangor and the Down East region. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... On Saturday night, a broad ridge of high pressure stretching from Greenland to Kansas will try to establish itself over the area, but low level moisture seems likely to remain trapped under a subsidence inversion and have adjusted Sunday`s highs a bit lower. Later on Sunday, low pressure in the southern Appalachians will start tracking towards the Mid-Atlantic coast. This low is expected to stay south of the area. Instead, a weakening cold front will cross the state on Monday with a few showers and cloudy skies. High pressure returns Tuesday into Wednesday with seasonable temperatures. How much sunshine will be determined by the wind direction and low level moisture advection. As this high pushes offshore by Wednesday, there`s hope for warmer temperatures late week...if low pressure moving up the Atlantic doesn`t block a strong upper ridge from arriving. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... NEAR TERM: Msly VFR late this aftn across the TAF sites will transition to MVFR clgs/vsbys with rn onset erly this eve then lowering to IFR with rn/sn mix at Downeast sites ovrngt and LIFR in all sn across Nrn TAF sites. Conditions improve to MVFR by Thu aftn and then to VFR Thu ngt following the passage of a weak cold front. SHORT TERM: Friday morning will start with mostly MVFR cigs except western locations such as Clayton and GNR which may be IFR due to cigs and snow. By afternoon, most terminals will become VFR. On Friday night, conditions will gradually lower to IFR to LIFR in snow...first towards FVE and spreading south to BGR by late night. On Saturday morning, all sites will likely start as IFR to LIFR in snow...except BHB...and gradually lift to MVFR during the afternoon. Sites north of PQI may stay IFR all day in light snow. Otherwise, MVFR cigs seem likely to persist into Sunday morning. Conditions should lift to VFR for Sunday afternoon and night. && .MARINE... NEAR TERM: Most models indicate winds and seas increasing to SCA ovr all of our waters by mid eve...contg well into the morn hrs Thu. Aftwrds, intially winds followed by seas will subside Thu aftn and ngt. Kept close to WW3 guidance for fcst wv hgts. SHORT TERM: There is potential for a marginal SCA later Friday into Friday night as a low pressure organizes near Cape Cod. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...None. MARINE...Small Craft Advisory until 11 AM EDT Thursday for ANZ050>052. && $$ Near Term...VJN/Dumont Short Term...MCW Long Term...MCW Aviation...VJN/Dumont/MCW Marine...VJN/Dumont/MCW is the U.S. government's official web portal to all federal, state and local government web resources and services.