Area Forecast Discussion
Issued by NWS Caribou, ME

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681 FXUS61 KCAR 212221 AFDCAR Area Forecast Discussion National Weather Service Caribou ME 621 PM EDT Fri Jul 21 2017 .SYNOPSIS... A cold front will cross the area this evening. High pressure will build across the region over the weekend. Low pressure will approach on Monday. && .NEAR TERM /THROUGH SATURDAY/...
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6:21 PM...A couple of areas of convection that we are closely watching this evening. The first is ahead of the cold front and is moving across parts of the Saint John Valley. The second area is well in advance of the cold front and extends from northern Piscataquis County to northern Washington County. The area of greatest concern at this time is across northern areas. Expect that the convection will weaken some with time this evening as we lose the daytime heating, but the northern storms will likely hold together better as they have more upper support with the approaching cold front. Previous discussion... Two separate areas of convection will affect the area this evening. The first is a pre-frontal trough with thunderstorm activity from northern Somerset County towards northern Washington County. This area has benefited from strong shear, diffluence aloft and the exit region of a potent upper level jet. The best CAPE has been mostly towards the eastern border of the state and this has been where the stronger storms have organized. There is also differential heating with temperatures in the mid to upper 80s south of the trough and in the 70s north of the trough. Straight line hodographs have yielded an interesting combination of right and left moving storms along the trough. Convection with the pre-frontal trough will tend to weaken with the loss of daytime heating and the upper jet pushing eastward out of the area. The actual cold front is the second area of convection which is bearing down on the Saint John Valley. Will leave enhanced wording for gusty winds and small hail until 9PM...after which thunderstorm activity will diminish. Residual shower activity with the front should be out of the area by midnight. After midnight, a very dry Canadian air mass will arrive with dew points dropping to the upper 30s and 40s. All areas will benefit from much lower humidity on Saturday. An onshore flow will ensure the warmest temperatures will be towards the coast where lower 80s are expected. In contrast, only upper 60s are forecast towards Fort Kent and Madawaska. There will be some fair weather cumulus at the top of a deep mixed layer. This mixed layer will yield some gusts towards 20 mph.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... The consensus of longer range models keeps fair, cool, and dry conditions to the Rgn Sat ngt thru Sun eve as a sfc ridge of Can hi pres crosses the area into NB prov. Clds will gradually increase from WSW to ENE across the Rgn late Sun ngt into Mon with shwrs/rn slowly spreading into Wrn ptns of the FA from Srn QB by Mon aftn. Rather than to rely solely with the latest 12z dtmnstc GFS, which was sig faster and further N in bringing rnfl into the Rgn, we kept with a consensus blend of models which keeps the leading edge of shwrs from reaching far Nrn ptns of the Rgn til late Mon aftn. Shwrs will then affect all of the Rgn Mon ngt thru Tue as the sfc low tracks alg the Downeast coast and the upper trof crosses all of the Rgn. Most QPF though, will occur ovr interior SW and Cntrl highlands areas spcly later Mon into Mon eve when there may be enough CAPE for sct tstms, and the least across the far N. Subsequently, hi temps Mon and Tue will be coolest ovr Wrn most ptns of the Rgn on Mon and Tue. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Shwrs should quickly exit the FA Tues eve as the upper trof moves E into the Can Maritimes. Fair and somewhat warmer conditions will return for Wed as a mdtly strong s/wv ridge alf crosses the Rgn. Longer range models cont to show a msly unsettled pattern alf...indicating another s/wv trof complex apchg and crossing the the Rgn from S cntrl QB with additional shwrs keeping hi temps at or below avg for this tm of season. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... NEAR TERM: VFR is expected outside of thunderstorms this afternoon and evening. No prolonged cigs are expected Saturday, but northwest winds may gust towards 20 kt. SHORT TO LONG TERM: VFR conditions xpctd all TAF sites with MVFR clgs/vsbys possible with heavier shwrs Mon aftn thru Tue. && .MARINE... NEAR TERM: No significant weather is expected. Winds will stay up towards 15 kts ahead of the cold front this evening. SHORT TO LONG TERM: No immediate hdlns slated for these ptns of the fcst for our waters with wv hts ovr outer most waters apchg 5 ft ovr outer most waters Mon aftn into Mon ngt with primary wv pds ranging from 5 to 9 sec. Went with about 85 percent of WW3 wv guidance. && .CAR WATCHES/WARNINGS/ADVISORIES... ME...Beach Hazards Statement until 8 PM EDT this evening for MEZ029- 030. MARINE...None. && $$ Near Term...CB/MCW Short Term...VJN Long Term...VJN Aviation...CB/MCW/VJN Marine...CB/MCW/VJN

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