Area Forecast Discussion
Issued by NWS Burlington, VT

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244 FXUS61 KBTV 172254 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 554 PM EST Sun Dec 17 2017 .SYNOPSIS... Surface high pressure cresting over the North Country will bring seasonably cold and quiet conditions through the first half of tonight. A warm front approaching from southwestern New York will bring increasing cloudiness and widespread light snow for Monday morning into early Monday afternoon. Snow accumulations between 1 and 3 inches are generally expected, with localized totals around 4 inches for the southern Green Mountains. A brief warm up is expected on Tuesday, with gusty south to southwesterly winds. A frontal passage Tuesday evening will bring a few rain or snow showers and a return to colder temperatures. The next chance for significant precipitation will arrive Friday night into Saturday. A low pressure system passing to the west of the region is expected to bring mixed wintry precipitation, transitioning to plain rain as warmer air moves in on southerly winds. && .NEAR TERM /THROUGH MONDAY NIGHT/... As of 554 PM EST Sunday...Overall forecast in good shape with just some tweaks to match current temperatures...which are wide ranging at this time given relatively clear skies and light winds. Eventually thicker cirrus will move in and temperatures should stop falling and in some locations warm back up slightly. Going forecast has this covered well. Previous Discussion... A period of light snow 12-18Z Monday will produce a general 1-2" snowfall across the region, with localized totals 2-4" across the spine of the Green Mtns and across portions of southern St. Lawrence and Franklin NY counties. While not a significant event, may see a few travel slowdowns across the region Monday morning into early Monday afternoon with snow covered roads and brief periods of visibility less than one mile. We`ve made this the focus of our social media posts this afternoon and included mention in the Hazardous Weather Outlook. In the meantime, looking at a quiet evening and first half of the night as 1030mb sfc anticyclone crests over the North Country and srn Quebec before shifting ewd. This will result in light winds and good radiational cooling after sunset. By midnight, should see 2-meter temperatures generally zero to 10 above, and locally falling below zero across far nern VT. Will see temperatures level off after 06Z Monday - or rise slightly - with increasing high- mid level clouds from SW-NE in advance of modest warm front across the srn tier of NY. Likewise, light S-SE winds will develop after midnight. Should see sufficient isentropic lift to allow light snow to develop starting around 11Z across the nrn Adirondacks and Rutland county, and lift nwd into the Champlain Valley by 12Z or so. Combined with modest mid-level height falls as a shortwave trough progresses ewd along the intl border, will see a widespread light snowfall across the area thru 18Z or so. With warming aloft, will see snow-to-liquid ratios drop into the 12:1 to 14:1 range. Best forcing for ascent shifts ewd during Monday aftn, with some continued orographic snow in the Green Mtns and across the Adirondacks. Temperatures will not be as cold, with highs Monday generally 25-30F, except lower 20s with localized nely winds in the St. Lawrence Valley, and across far nern VT where low-level cold air will be slower to scour out. Monday night will feature continued overcast conditions and light S-SW winds, increasing a bit toward daybreak Tuesday (5-10 mph). Temperatures will hold relatively steady in the mid- upr 20s and slowly rise to near freezing by daybreak Tuesday. Not much large- scale ascent, but continued light precipitation across the nrn Adirondacks and nrn Greens will remain possible with sw low-level flow and orographic ascent. Slowly warming thermodynamic profiles may allow for intervals of sleet or even plain rain in swrn St. Lawrence county. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY/... As of 342 PM EST Sunday...A shortwave strengthening over the Great Lakes Region will slightly amplify the upper-level flow Tuesday evening and provide some stronger support aloft than Monday. This will result in precipitation over northern New York/Vermont becoming increasingly widespread into Tuesday evening when the best dynamics move into the area. At the same time, warmer air will continue to move into the forecast area Tuesday, working it`s way east from Northern New York early Tuesday morning and pushing into most of Vermont by early Tuesday afternoon. The low-level warm air will support a transition from snow to rain throughout the morning. Some mixed precipitation is possible in areas of northern New York early Tuesday morning and in the Northeast Kingdom of Vermont mid-day as cold air at the surface takes a little longer to erode. Tuesday night into early Wednesday morning, a cold front will push into New England from southern Quebec, thus ending our brief early week warmup. Colder air moving in will cool the entire column back to below freezing, allowing precipitation to changeover back to all snow throughout the morning Wednesday. Flow will become increasingly northwesterly midweek as the weakly amplified upper- level longwave trough progresses downstream. Some lingering moisture in the area Wednesday will support continued light snow showers, but in the absence of any real forcing, these will mainly be orographically focused. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 342 PM EST Sunday....High pressure centered over northern Ontario will edge into New England from the west Wednesday night, effectively ending any lingering precipitation. Thursday will be the driest and coldest day of the work week with daytime highs in the upper teens to low 20s. The next impactful system on the horizon will start off as a weak low forming in the lee of the Rocky Mountains Thursday afternoon. As the system tracks northeastward towards the western Great Lakes region Friday morning, it will intensify under favorable jet dynamics aloft. The low will then track into southern Ontario Friday night, pushing an associated warm front across the forecast area. The passage of the warm front will set off a brief but strong warmup Saturday morning before the cold front marches through Saturday afternoon/evening. The system will spread precipitation over the area, however precipitation type will depend greatly on the exact track of the low. Subsequent model runs of the ECMWF and the GFS continue to shift the track of the surface low north and west, which would put northern New York and Vermont solidly in the warm sector of the cyclone by Saturday morning. At this time, the current forecast reflects this solution. Current thinking is that we`ll see some light warm air advection snow initially Friday morning, followed by a transition to rain Friday night through Saturday morning. After the cold front pushes through Saturday night, precipitation will taper off and change back over to some light snow. It`s worth noting that this system is still a ways out in the forecast and the impacts to the forecast area are highly dependent on the exact track the low takes. As the system departs the area, a colder arctic air mass will be ushered in from Canada. Looks like next week will likely feature the coldest temperatures of the season thus far for Vermont/northern New York. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Through 18Z Monday...Mostly clear/VFR conditions are anticipated through 06Z Monday. The only exception will be some lake induced low cloudiness in vicinity of Lake Champlain, which will cause ceilings 1-2kft around PBG through mid-late afternoon before dissipating. High and mid-level cloudiness will be on the increase overnight. An approaching warm front from the southwest will bring IFR/light snow to all TAF locations generally 12-18Z Monday, perhaps beginning a bit earlier (11Z) at SLK/RUT. Will see HIR TRRN OBSCD at times due to snow and lowering ceilings during the day Monday. Snow accumulations of 1-2" are generally expected for the TAF locations, with minor impacts to aviation ground operations foreseen 12-18Z Monday. Light winds this afternoon and overnight...becoming SE/S at 5-10kts during the daylight hrs Monday. Outlook... Monday Night: MVFR/IFR conditions possible. Slight chance SHSN. Tuesday: Mainly MVFR, with local VFR possible. Chance SHRA, Chance SHSN. Tuesday Night: Mainly VFR, with local MVFR possible. Chance SHSN, Chance SHRA. Wednesday: Mainly VFR, with areas MVFR possible. Chance SHSN. Wednesday Night: Mainly VFR, with areas MVFR possible. Slight chance SHSN. Thursday: Mainly VFR, with areas MVFR possible. NO SIG WX. Thursday Night: VFR. Chance SN. Friday: Mainly VFR, with local MVFR possible. Chance SN. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...Evenson/Banacos SHORT TERM...RSD LONG TERM...RSD AVIATION...Banacos is the U.S. government's official web portal to all federal, state and local government web resources and services.