Area Forecast Discussion
Issued by NWS Portland, ME

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742 FXUS61 KGYX 052059 AFDGYX Area Forecast Discussion National Weather Service Gray ME 359 PM EST Mon Dec 5 2016 .SYNOPSIS...
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High pressure moves in from the west tonight and crosses through the area on Tuesday. A weakening trough of low pressure approaches from the west Wednesday morning with more light snow possible. A cold front arrives from the northwest on Friday ushering in some of the coldest air of the season so far for this weekend.
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&& .NEAR TERM /TONIGHT/...
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Weak low pressure in the Gulf of ME will continue E tonight. Within the last couple of hours MWN has gone to W winds...indicating that the upper trof is passing thru at least some of the forecast area. This corroborates drying on the latest WV satellite imagery. As this trof axis passes...snow will wind down from W to E. It has ended across much of NH at this hour...and will do so in ME zones over the next few hours. As the snow ends...coastal front will slide back out to sea from areas near the coast and capes where it worked inland. This temp drop could result in some refreezing on roadways...so slick conditions will linger into the evening. The W flow and lingering low level moisture will result in some upslope snow showers tonight too. And I have left high PoP in the NW slopes to account for these...and they may be persistent enough for another inch or two on top of what has already fallen today.
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&& .SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
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S/wv ridging and high pressure move in for Tue. Much of the day will be clear and comfortable temps for this time of year. The main focus is on a Southeast s/wv trof that will be lifting towards the Mid Atlantic during the day. The wave will be shearing out with time however...and model guidance pretty rapidly weakens forcing for ascent as precip enters the forecast area. Initially isentropic lift is modest for parts of Wrn New England...but this gradually wanes by early afternoon. Lift will mainly be tied to the passage of the upper trof...and so snowfall looks likely but amounts at this time look to be less than an inch. Timing is probably the more important factor...as snow will be arriving around or during the morning commute in NH.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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Broad troughing in the center of the continent will shift east into New England later this week as the core of the upper level low moves east into eastern Canada. As this low moves northeast the flow behind it will become more zonal in its wake. A broad trough moving into the west coast on Friday will track east across the country this weekend, possibly brewing up a storm for early next week as it arrives into New England. The details: By Wednesday morning northern New England will be caught in between two disconnected waves, one moving out to sea south of New England and the other associated with the upper low moving through the Great Lakes and southern Canada. An area of lift along a weak trough between the two will generate some light snow as it moves into western New England Wednesday morning, but as it moves east it will lose a lot of its support with the precipitation dissipating as it arrives into our area. Expect the best chance of snow and greatest accumulations to occur across western and southwestern New Hampshire where 1 to 2 inches is possible. Further east should see some flurries or up to an inch. This will be arriving around the time of the morning commute, so even the light accumulations could cause some slick roadways. Models had been advertising another wave moving nearby on Thursday, possibly generating offshore low pressure and snowfall for our area. However, models are generally in good agreement now that this will not happen at all. Instead, the primary upper trough moves through the area on Thursday, eventually generating low pressure well out to sea tracking into the Canadian Maritimes on Thursday. The result is near normal temperatures on Thursday with a cold front moving through Friday night turning temperatures colder for this weekend. The cold northwest flow on Friday will allow some downslope warming (into the mid 30s anyway) for the coast, but the mountains will stay in the 20s. On Saturday it will be even colder with the entire region staying in the 20s. Saturday night is shaping up to be the coldest night of the year so far as surface high pressure moves east into the area. Still a good amount of uncertainty on how well the various pieces will align for a great radiational cooling night, but for now expect widespread teens with single digits in the typical cold spots. This forecast could be too warm if the high moves into the area a little earlier or clouds stay away more than currently forecast. Models not in very good agreement on the timing and strength of the wave moving across the country this weekend and arriving in New England early next week. The GFS brings a sharp trough into New England Sunday night and spins up a coastal low with some snowfall on Monday, while the ECMWF holds the trough back and doesn`t arrive until Monday night with a potentially warmer scenario unfolding. For now it is only safe to say that there is the potential for some precipitation early next week and that precipitation type and amounts are still quite uncertain.
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&& .AVIATION /20Z MONDAY THROUGH SATURDAY/...
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Short Term...Widespread IFR conditions continue across much of SWrn ME. As upper trof passes...and coastal front shifts back out to sea dragging colder air behind it...conditions will improve to VFR. AUG will remain IFR the longest...while RKD may bounce back to IFR as the coastal front slips back out to sea and they go from RA back to SN. NW flow however will keep clouds stuck in upstream of the mtns...so I anticipate HIE to remain at least MVFR with occasional SHSN thru the night. High pressure Tue brings VFR conditions to all terminals. Very late Tue night SN will move back into the area from the SW to NE. SW NH terminals like LEB...MHT...and CON are most likely to see some IFR before 12z Wed. Long Term...Conditions deteriorate from west to east Wednesday morning with snow moving in. This will dissipate as it moves east, so the most likely airport to be affected will be Lebanon with lower chances east of there. Still could hang on to an MVFR or at times IFR ceiling across most of the area on Wednesday before clearing out Wednesday evening. A northwest flow Thursday into the weekend will bring a chance for upslope snow showers in the mountains and Whitefield could be MVFR most of that time period.
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&& .MARINE...
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Short Term...As upper trof passes and weak low pressure moves into the Gulf of ME...winds will become NWly and increase. Model forecast soundings snow mixing enough to get a few gusts close to 25 kts...but more likely below that. Seas will increase as well...but to around 4 ft on the outer waters. At this time I have not issued a SCA...but a brief window of marginal SCA conditions would not be surprising around 06z. High pressure moves over the waters Tue...with winds and seas diminishing. NE flow returns Tue night as the next warm front approaches from the SW. Long Term...Offshore winds expected on Thursday, increasing Thursday night into the weekend as a cold front brings in colder air from Canada. This will likely lead to a period of advisory level wind speeds.
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&& .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Legro SHORT TERM...Legro LONG TERM...Kimble

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