Area Forecast Discussion
Issued by NWS Burlington, VT

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191 FXUS61 KBTV 072344 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 644 PM EST Wed Dec 7 2016 .SYNOPSIS... An unsettled pattern is expected across the North Country through the end of the week...with occasional snow showers and isolated snow squalls...as temperatures drop to below normal levels by the weekend. Total snow accumulations of 3 to 6 inches with isolated higher amounts will be possible south of Route 3 in Saint Lawrence County and the northern mountains of Vermont and New York. A dusting to several inches possible in the valleys with periods of hazardous travel possible. && .NEAR TERM /THROUGH THURSDAY NIGHT/...
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As of 629 PM EST Wednesday......Lake snow advisory continues for Southern Saint Lawrence County mainly south of Route 3 for 4 to 8 inches of snow by Thursday Night... Not much to add for the evening update. Some small adjustment to temps in the St Lawernce Valley as the saw a brief period of clearing before sunset that gave them a little extra heating and warmer than expected temps. Timing still looks good for snow to begin in the St Lawrence Valley after 08z. Previous Discussion...Forecast challenge will be timing of snow showers and squalls across our region...along with potential impacts and accumulation. Large picture shows closed 5h/7h circulation over the northern Great Lakes with broad southwest flow aloft across the northeast conus. Watching increasing mid level moisture and weak elongated vort over the central/northern plains moving our way for Thursday. This energy and moisture aloft...will combined with cooling thermal profiles to produce occasional snow showers and isolated snow squalls across parts of our region. High resolution models show ingredients coming together with instability...moisture...and favorable southwest aligned flow around 12z Thursday across central Saint Lawrence County. Latest 4km NAM and locally developed BTV 4km shows this band intensifying btwn 15z-21z Thursday...as low level instability increases from surface heating and cooling aloft associated with trof and deeper moisture feed from Lake Ontario. Very difficult to determine organization of band without a sharp convergence line and limited deep layer moisture...but thinking snowfall rates of up to 1 inch per hour are possible. Qpf/snowfall is the greatest from southern Saint Lawrence Valley into the northern mountains of vt near Jay Peak where snow accumulations of 2 to 6 inches are likely with isolated higher amounts. Elsewhere...away from the most persistent lake effect snow shower activity...a dusting to several inches is possible. Have noted high resolution data shows intense omega couplet...along with favorable moisture in snow growth area at BTV around 18z Thursday...along with a quick 0.05 to 0.10 of qpf...which could produce a burst of 1 to 2 inches of snow right before evening commute. This band is progged to shift south and dissipate across central/southern vt by 21z Thursday. Temps mainly in the mid/upper 20s to mid 30s...but falling back into the teens and 20s on Thursday Night. Forecasting these events are difficult with timing and intensity...but something we will watch very closely over the next 12 to 18 hours. Thursday Night...mid/upper level trof deepens with leftover 850 to 500mb moisture in the trof axis. This combined with developing upslope flow and moderate low level cold air advection will produce a period of favorable upslope snow from 03z to 12z Friday. Soundings show good moisture in snow growth region...along with enhance 1000 to 700mb omega across the northern dacks into the central/northern green mountains from near Sugarbush to Stowe to Jay Peak. Have increased pops to likely/cat...including the eastern cpv...associated with some lake champlain moisture enhancement. Expecting a high fluff factor with additional snow accumulations of 2 to 6 inches in the mountains and another inch or so across the eastern champlain valley. Temps drop to near normal for lows ranging from the teens to mid 20s.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 300 PM EST Wednesday...Work week ends with surface low pressure continuing to pull northeast through the Canadian maritimes while cyclonic mid/upper flow persists across the North Country. Higher elevation upslope snow showers persist through much of Friday on west/northwest flow, with a few more inches of snow possible generally above 1000 feet, but activity will begin to dissipate going into Friday night as surface high pressure builds into the Ohio Valley. Temperatures will be slightly below seasonal normals with highs in the mid/upper 20s to lows mainly in the teens. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 300 PM EST Wednesday...For Saturday and Saturday night aforementioned high pressure builds into the northeast with dry conditions expected. Aloft the mid/upper flow remains out of the west/northwest so despite strong subsidence at the surface, feel we`ll see a good deal of clouds around. Strong cold air advection on the front-side of the high will continue to provide below normal temperatures with highs only in the teens to 20s, and widespread single digits to low teens for lows Saturday night. For Sunday onward, large uncertainty continues to exist with the forecast with increased model differences from the 00z suite in the handling/phasing of energy pulling out of the lee of the Rockies Saturday night. Latest ECMWF and CMC continue to offer a deeper trough with the ECMWF phasing with the northern stream pulling a robust surface low northeast through the Ohio Valley Sunday night and the St. Lawrence and Ottawa Valleys through Monday night. The CMC however does not phase, keeping the surface low more suppressed to the south, and the GFS while it does phase with the northern stream offers a much weaker trough and surface low with little impacts. Your guess is as good as mine as to what happens here, so for now I`ve offered a blended model approach with mid-chances for some light snow. Models do come into better consistency though heading into the middle of next week behind whatever system we get for Monday/Tuesday. The trend here will be towards much colder air with possibly our first arctic outbreak as a deep cold low settles over southern Ontario/Quebec and strong surface high pressure develops over the central CONUS. Coldest air looks to arrive beyond this forecast period though, so stay tuned. && .AVIATION /00Z Thursday THROUGH Monday/...
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Through 00Z Friday...Overall VFR conditions across the region with KSLK still lingering with MVFR ceilings. Expecting VFR for most locations with short periods of potential MVFR/IFR with brief passing snow showers tomorrow. KSLK should see the worst with possible IFR/LIFR conditions possible on Thursday. Light southerly winds at 05-10 knots overnight should give way to a southwesterly direction tomorrow with the St Lawrence Valley also seeing a gustier 10-20 knots in the afternoon. Outlook 00Z Friday through Monday...Occasional snow showers with a brief snow squall possible btwn 00z-06z Friday...with rapid change in vis/cigs likely in any snow squall. After 00z snow showers become confined mainly to the mountains with ifr conditions lingering at mpv/slk through 12z Friday. Mvfr cigs linger at slk/mpv on Friday with vfr developing Friday night into Sunday. Next system arrives on Sunday afternoon with another widespread light snow event. This system will produce widespread ifr conditions between 18z Sunday into 12z Monday.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...Lake Effect Snow Advisory from midnight tonight to midnight EST Thursday night for NYZ029. && $$ SYNOPSIS...Taber NEAR TERM...Taber/MV SHORT TERM...Lahiff LONG TERM...Lahiff AVIATION...Taber/MV

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