Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 062352 AFDGYX Area Forecast Discussion National Weather Service Gray ME 652 PM EST Wed Dec 6 2017 .SYNOPSIS... Weak high pressure will gradually build into the region through Friday with generally fair weather expected for most of the area. Some upslope snow showers will linger north of the notches into Thursday before dissipating. The pattern change begins to take hold this weekend...as a coastal low will develop offshore Saturday. This may deliver a little light snow to the coastal plain through Saturday night. Beyond the weekend we will have to watch for another coastal low developing offshore...especially midweek...that could deliver some snow to the region but confidence is currently low. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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650 pm Update: Skies mostly clear across the region as forecast. Input latest mesonet data with only minor tweaks to temps needed. Quiet night ahead. Previous Discussion: Cooler air is slowly seeping into the forecast area from the NW this afternoon. Upstream a secondary S/WV trof will bring another shot of colder air tonight. This wave will also help to focus moisture and flow over the higher terrain...especially across the NH North Country. As flow becomes more Wly...that may also bring some lake enhanced moisture...as the Lake Ontario streamer becomes more oriented towards the NWrn forecast area. Some light accumulations are possible in those Nrn zones.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Cyclonic flow continues around upper low over Nrn Quebec. Trapped low level moisture enhanced by the Great Lakes will continue to flow over the high terrain. In addition it looks like late Thu lift may be aided by a passing S/WV trof. Snow showers should continue N of the notches into Thu night. Gradient flow and CAA will keep low temps fairly well mixed and close to normal. Forecast soundings indicate that the atmosphere will remain well mixed in the low levels tonight, so temperatures will not fall as much as they otherwise could. Lows will generally be in the 20s, with some colder temperatures possible in well protected valleys. Westerly flow continues on Thursday with temperatures near normal, in the upper 30s and low 40s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... The deterministic solutions are in good agreement on the long wave pattern through the entire forecast period. The well advertised pattern change to a high amplitude western ridge and eastern trough across the CONUS will remain locked in place. This will provide the region with an extended period of below normal temperatures as the door remains open for reinforcing shots of arctic air into the Great Lakes and northeast CONUS. We begin the period with the trough axis stretching from the western Great Lakes southward into Texas. We`ll be in south-southwest flow aloft and under weak surface ridging sandwiched between an offshore baroclinic zone and a weak surface system over the Great Lakes. The flow aloft will back a bit for Friday night and Saturday with the offshore baroclinic zone retrograding a bit closer to the coast. The western edge of the cloud shield will move onshore as well...but at this time it appears the measurable precipitation should remain offshore. The baroclinic zone is finally kicked well offshore on Sunday as the upper trough axis propagates further eastward to vicinity of the appalachian range. The close proximity of the upper trough and a passing shortwave impulse will produce clouds and a few snow showers...especially across the higher terrain. Weak ridging briefly takes hold for Sunday night and early Monday. Digging shortwave energy over the western Great Lakes will carve out a full latitude trough over the eastern seaboard by Tuesday. A cold front will approach the area by late Monday then slow down in response to the upper trough and falling heights. Tee front will crawl across the region on Tuesday with cold air injection leading to significant cyclogenesis near the coast or nearby offshore. There remains considerable differences on timing with shortwave impulses and how fast the upper trough goes negative tilt. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... Short Term...With W flow and CAA...downsloping off the mtns will lead to widespread VFR conditions S of the high terrain. Along the NW slopes...MVFR CIGs are possible into Thu afternoon. Some SHSN are possible in the vicinity of HIE tonight into early Thu...but should focus N of the terminal. Long Term... Sat...Lcl MVFR psb in -shsn vcnty of the coast. Sun...Sct MVFR psb in -shsn. && .MARINE... Short Term...W to SW flow will continue thru Thu. This will at least allow seas to remain near 5 ft. Winds will most likely gust closer to 20 kts...but it is close enough that I extended the SCA outside the bays thru Thu afternoon. Conditions will remain near SCA thresholds in CAA into Thu night. Long Term... Mon...Small Craft conditions are possible. && .TIDES/COASTAL FLOODING... Winds will continue west to southwest thru Thursday. Wave action will diminish to a more 4 to 5 ft range. Considering those factors and a high tide closer to 11 ft...any splashover threat will be smaller Thursday. Some minor beach erosion could still result around high tide however. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory until 11 AM EST Thursday for ANZ150-152- 154. && $$

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