Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 172023 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 323 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/...
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As of 256 PM EST Sunday...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 snowcovered 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.
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&& .SHORT TERM /TUESDAY/... As of 249 AM EST Sunday...A warm front will lift across the region Monday night, allowing light precipitation to redevelop after a very brief break. Lows will be early with temperatures holding steady or rising overnight. This warming will continue through Tuesday afternoon; temperatures will reach into the mid/upper 30s to around 40. Therefore, expect Monday night`s light snow will transition to at least a rain/snow mix, if not just plain rain, just about everywhere. Accumulating snowfall will be minimal since the increasing temperatures will lower snow ratios. The highest elevations may see up to 2 inches through Tuesday afternoon, but most locations should get less than an inch. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 249 AM EST Sunday....Showers will continue through Tuesday night as the upper shortwave and surface cold front sink southward across the region. Rain showers will transition to snow and become more focused in the favorable upslope areas as winds turn to the northwest behind the front. These snow showers will linger through much of Wednesday. Much colder air will follow the frontal passage; although Wednesday`s highs will be in the 20s most spots, temperatures will drop down into the single digits Wednesday night and again on Thursday night, while Thursday will only see highs in the teens to around 20. The focus then turns to a potential storm system for Friday and Saturday. Although the long range models still differ on the details, it is looking more likely that low pressure will slide along or even north of the Saint Lawrence River valley later Friday through Saturday. This would place us well into the warm sector, particularly if the 00z/17 ECMWF`s northern solution proves correct. Have noted that critical thickness progs on both the latest GFS and ECMWF indicate there could be some mixed precipitation in the snow to rain transition zone Friday afternoon. Given the very cold airmass that will exist ahead of this system, this is very much within the realm of possibility. Have stayed with rain/snow wording for now, but the potential for a period of a wintry mix will have to be monitored. Regardless, expect all areas will transition to plain rain by midnight Friday night and then remain so through much of Saturday. Then the rain will transition back over to snow as the cold front marches from west to east Saturday afternoon. Persons with travel plans at the end of the week should monitor forecasts closely as we are still several days away and changes are possible. && .AVIATION /20Z SUNDAY 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...Banacos SHORT TERM...Hastings LONG TERM...Hastings AVIATION...Banacos

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