Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 170340 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1040 PM EST Thu Nov 16 2017 .SYNOPSIS...
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A cold front moving through northern New York and Vermont this evening will bring rain showers, gradually changing to wet snow during the overnight hours. Some light snow accumulations are possible early Friday morning, especially across the northern slopes of the Adirondacks and western slopes of the Green Mountains and across the higher summits. A few icy spots are possible for the morning commute on Friday. Dry weather returns for Friday afternoon as a weak area of high pressure moves in before the next low pressure system brings another round of rain and snow along with gusty winds for Saturday night and Sunday.
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&& .NEAR TERM /THROUGH FRIDAY NIGHT/...
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As of 1029 PM EST Thursday...Secondary 700mb trough and associated surface cold front has shifted east of the Champlain Valley at 0315Z. Developing WNWLY flow behind the front and frontal inversion is beginning to result in orographic blocking, with enhanced reflectivity developing along the nrn slopes of the Adirondacks and across the Champlain Valley into the wrn slopes of the Green Mtns. This trend should continue thru the remainder of the overnight hrs. Concurrently, low-level CAA will allow temperature profiles to cool enough to change rain over to snow. Already down to 30F with light snow at SLK, and should see temperatures near freezing at BTV by 10Z. May see some developing icy spots on roadways for the morning commute, especially across the wrn slopes of the Green Mtns where orographic enhancement and cooling temps will combine the most favorably. No significant changes to snowfall amts through 12Z...generally a coating to 0.5" across the northern valleys. May see first measurable snow of the season at BTV. Could see 2-3" for the higher summits from Camels Hump to Mt. Mansfield to Jay Peak. Previous Discussion...As the front moves across the region through 03Z, winds will shift to the west northwest transitioning the character of precipitation to be more orographic with forecast froude numbers (<0.5) indicating highly orographically blocked flow. This setup favors the highest chances of snow showers to be along and just west of the spine of the Green Mountains, but may just be blocked enough to back the moisture up enough that even Burlington gets in on some snow shower activity and perhaps a dusting to perhaps the first measurable snow of the season here at the airport. For elevations from about 750-1500 feet a general 1-3" of snow is expected while at the mountain summits above 3000 ft several more inches are likely, possibly up to 6". Secondary issue to the precipitation overnight will be brisk northwesterly winds and falling temperatures. Strong pressure gradient behind the front will develop winds in the 20-30 mph range helping to usher in strong cold air advection with temperatures falling below freezing everywhere by morning with lows mainly in the 20s perhaps near freezing on Lake Champlain so any snow that falls will be icing up especially in the higher terrain. Some snow showers linger across central and northern Vermont going into Friday mid-day, but by the afternoon sunshine should break out as high pressure builds in across the mid-Atlantic and Northeast states. Winds remain brisk from the northwest, and this combined with air temps topping out in the 30s will create some decent wind chills through the day in the teens and 20s. The high centers over the region Friday night with clearing skies for the first half of the night, and some high clouds building in from the west ahead of our next system. Shouldn`t affect temps from plummeting into the teens and 20s area-wide with some single digits possible in the Adirondacks and Northeast Kingdom, while warm air advection riding in aloft will keep the highest peaks in the 20s warming into the lower 30s.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 358 PM EST Thursday...On Saturday a large low pressure system is set to impact the North Country. The system is expected to bring a mix of rain/snow/sleet as it progresses into the region with a return to snow as the system exits Sunday night. The 500mb trough on Saturday will be amplifying into a full latitude trough with a deepening surface low over the Ohio Valley region. That low will track northeast through Lake Erie and Ontario into the Saint Lawrence valley or just north. The surface track will lead to warm air advection surging into the North Country on Saturday along with the leading edge of the precip shield. Guidance continues to back off on the timing of precip and so I`ve pulled back the arrival of precip until mid to late afternoon on Saturday. With the delayed timing, there`s an increasing chance for the warmer nose aloft to work into the region and cause some mixed precip to fall. Given uncertainty in timing, I`ve continued to just mention the boundary layer impacts of either rain or snow because its a tad early to feel confident in specific mixed precip type. By Saturday evening the warm air will be fully into the area and full melting will occur with rain expected for the bulk of the overnight hours. The surface low should be just over the Saint Lawrence valley Sunday morning and there`s growing evidence that the dry slot may work into the forecast area by early Sunday morning. The impact of this is two fold, one our precip could come to an end early, and second the pressure driven winds will start to see some mixing of the stronger low level jet. Based on the latest blends of guidance I`ve indicated gusts of 35-45 mph will be possible in the Saint Lawrence with 30-35 across the rest of the Champlain Valley and Vermont. Much of this will be dependent on how much mixing occurs and the stability of the region. The cold front clears the North Country Sunday afternoon and cold air aloft returns switching any remain precip back to snow. With northwest flow aloft the western slopes should pick up some measurable snow due to orographic effects. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 423 PM EST Thursday...High pressure builds into the North Country to start the work week and other than a weak clipper expected to bring some lake effect snow over Northern New York the longer term forecast remains quiet with near normal temps which will be beneficial for travel during the holidays. The clipper system has some potent energy but much of that stays too far north to impact the forecast area. Expect Lake Effect snow with some orographic enhancement on Wednesday into Wednesday evening with a return to dry weather for Thanksgiving Afternoon/Evening. && .AVIATION /04Z FRIDAY THROUGH TUESDAY/... Through 00Z Saturday...Flight conditions through most of the next 24 hours will be largely MVFR with periods of IFR possible in snow during the overnight hours. Scattered rain showers this evening will be changing to snow towards midnight before ending. Precipitation will be mainly ties to the higher terrain, affecting KSLK and KMPV the most, but will also occasionally make it into BTV and other valley locations. After 15Z Friday, conditions will trend back to VFR as high pressure builds in. Winds will also be a factor through the period, gusty from the south/southwest this afternoon, and then west/northwest mainly after 02-04Z with gusts 20-30kts likely. Falling temps may lead to icy runways by morning. Outlook... Friday Night: VFR. NO SIG WX. Saturday: Mainly VFR, with local MVFR possible. Likely SHRA, Chance SHSN. Saturday Night: Mainly IFR, with areas MVFR possible. Likely SHRA, Likely SHSN. Sunday: Mainly MVFR, with areas IFR possible. Windy with gusts to 35 kt. Chance SHRA, Chance SHSN. Sunday Night: Mainly MVFR, with areas VFR possible. Chance SHSN. Monday: Mainly VFR, with areas MVFR possible. Slight chance SHSN. Monday Night: Mainly MVFR, with areas VFR possible. Slight chance SHSN. Tuesday: VFR. Slight chance SHRA, Slight chance SHSN. && .MARINE... As of 349 PM EST Thursday...A Lake Wind Advisory remains in effect for tonight into Friday. Calmer winds this afternoon ahead of a cold front passage will quickly increase again after midnight, turning to the west northwest at 20 to 30 knots through mid-morning Friday. Anyone out boating will need to be aware of the rough conditions that will result from the strong winds. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Lahiff NEAR TERM...Banacos/Lahiff SHORT TERM...Deal LONG TERM...Deal AVIATION...Lahiff/Verasamy MARINE...Lahiff

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