Area Forecast Discussion
Issued by NWS Burlington, VT

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343 FXUS61 KBTV 250749 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 349 AM EDT Tue Oct 25 2016 .SYNOPSIS...
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A trough of low pressure will continue to produce brisk winds and chilly temperatures through midweek with scattered mainly mountains snow showers. Temperatures will be in the 30s mountains to lower 40s valleys today and Wednesday. A widespread precipitation event is expected on Thursday into Friday with some snow accumulation likely in the mountains and breezy southeast winds along the western slopes.
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As of 347 AM EDT Tuesday...Water vapor shows deep cyclonic flow associated with mid/upper level trof across the northeast CONUS...with sharp moisture gradient from very dry air central NY to some mid level moisture northern New England. The combination of this moisture...with favorable upslope flow will produce mainly mountain focus snow showers today. So far activity has been very limited due to the very dry low levels and lack of upper level support. Thinking as weak embedded vort in the flow aloft drops across our northern cwa between 15z-20z today and interacts with some instability from surface heating...scattered valley rain and mountain snow showers will develop. Hi resolution composite reflectivity progs show popcorn nature to returns...with greatest concentration over the northern mountains. Will continue to mention likely pops northern green mountains from Mansfield to Jay Peak with a dusting to several inches possible. Elsewhere...will mention slight to chance pops...with some enhancement possible on the east side of Lake Champlain associated with lake effect. Would not be surprised to see a few wet snow flakes in the valley....given the chilly 925mb to 850mb thermal profiles. Models in good agreement of values between -7c and -9c today at 850mb and -1c to -3c at 925mb...these temps support highs low/mid 30s mountain towns and upper 30s/lower 40s warmer valleys. Still expecting breeze northwest winds at 10 to 20 knots with some locally higher gusts especially midday. Tonight...areal coverage of any leftover precip will dissipate by drier air at all levels develops across our region. Will mention chance pops mainly in the mountains...and will still need to watch the potential for some lake effect clouds and flurries on east side of champlain overnight. Temps will cool into the lower/mid 20s mountains to lower/mid 30s valleys.
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&& .SHORT TERM /WEDNESDAY/... As of 332 PM EDT Monday...The upper level trough will slowly drift towards the east as persistent cold air advection continues to provide below normal temps in the short term through the mid week. The continued northwest flow aloft will cause some light upslope snowfall. The flow will be unblock so areas with the highest accumulations will be in the western upslope locations such as Underhill, Jericho, Bolton etc. However with total qpf will be less than 0.10 which ultimately means we`ll only see an inch or two of snow fall. Wednesday we will be in sort of a lull between two systems. Expect cloudy conditions in the higher terrain with some breaks in the cloud cover in the Saint Lawrence and Champlain Valleys. The low and mid level moisture will be decreasing and so while the orographic forcing is still favourable for snow I dont anticipate much in the way of accumulation along the ridgeline Wednesday. The cold air advection even as a weak ridge starts to build in. Expect max temps to remain below normal as the entire column of air above 925mb is below 0C. Highs will be in the upper 30s to around 40 in the valleys. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... As of 425 PM EDT Monday...By Thursday the pattern picks up again with several chances for rain and snow. The upper level trough builds back in thus the upper level flow will remain west to northwest through the end of the week and into the weekend. The first surface low pressure system will track through the Great Lakes into New England on Thursday night and should bring quite a bit of warm advection to the area. The rain vs snow forecast will be quite tricky as the overnight temps will be supportive of snow however the warm air advection will be advancing rapidly with a southerly 850mb jet of 40-50kts bringing warmth from the Atlantic west of the spine of the Green mountains. However on the eastern side of the Greens the cold air will be trapped longer due to the high pressure system located over Nova Scotia. So I anticipate precip beginning first as snow across the entire area however by mid morning on Friday that will transition to a mix of rain and snow except for areas east of the Green mountains. Temp profiles in the higher terrain suggest they will stay all snow. The bigger issue will be the potential for gusty downslope winds. The track of the low pressure system will be critical as if the GFS is correct the low tracks across the CT/MA/NY border and the winds will be due east over the southern Green mountains. However the EC is slightly further north and thus the strongest winds dont turn east until the system is already east of the forecast area. If the GFS is correct there will be a 35-45kt 850m easterly jet over the southern Greens which would be supportive of downslope gusty winds. We will need to continue to monitor that as the forecast becomes clearer. Next system arrives late Saturday into Sunday with additional chances for precipitation however most of the guidance is warm enough that the system will produce mainly just rainfall. Based on GFS and EC soundings the entire column below 850mb is positive so based on the 12z suite of guidance I anticipate rain and max temps in the mid to upper 40s and lows in the 20s to mid/upper 30s. && .AVIATION /08Z Tuesday THROUGH Saturday/... Through 06z Wednesday...Mainly vfr conditions with occasional mvfr possible at mpv/slk this morning associated with lowering cigs and chances for mountain snow showers. The limited moisture both at the surface and aloft will limit impacts on tafs with regards to vis/cigs. Otherwise...still expecting breeze west to northwest winds 10 to 20 knots with a few higher gusts through today...before decreasing around sunset this evening at 4 to 8 knots. Outlook 06z Wednesday through Saturday... Active weather pattern continues with vfr trending toward mvfr/ifr Thursday into Friday. Expecting a period of snow at most sites on Thursday afternoon...with vis between 1-3sm...before changing to rain in the valleys by evening. Also...gusty southeast winds are possible...especially at rutland...creating areas of low level wind shear and turbulence. As winds shift to the northwest on Friday...ifr cigs are possible at BTV/RUT/SLK/MPV with areas of scattered rain or snow showers. Next system arrives late Saturday with additional precipitation and breezy southwest winds. Occasional mvfr/ifr conditions are likely by late Saturday. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Taber SHORT TERM...Deal LONG TERM...Deal AVIATION...Taber is the U.S. government's official web portal to all federal, state and local government web resources and services.