Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 080838 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 338 AM EST Thu Dec 8 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 TONIGHT/... As of 1203 AM EST Thursday......Lake snow advisory continues for Southern Saint Lawrence County mainly south of Route 3 for 4 to 7 inches of snow by Thursday Night... Current forecast remains in good shape with only some subtle tweaks to the chance for precip through the next couple of hours. KTYX is showing a weak band of showers extending off Lake Ontario but Watertown is reporting light rain. Expect as the band lifts further north that it will turn to light snow but there shouldn`t be much accumulation from it. The HRRR and our local WRF models seem to have a good grasp of the precip so I heavily blended that combination into the forecast through midnight. Otherwise no changes to the forecast were needed. 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. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 338 AM EST Thursday... 500mb trough with embedded vorticity will see continued chance for snow showers Friday, followed by slight ridging Friday night/early Saturday morning. Overall NW flow and Froude forecasts support light orographic snow showers. Surface high pressure builds in late Saturday, bringing an end to snow showers across the regions. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 338 AM EST Thursday...Active pattern continues in the long term with multiple shortwave energy moving through the North Country. The first arrives Sunday with snow showers. This looks to be followed by a more significant system Monday. Currently 00Z guidance showers surface low moving from the Ohio River valley to the coast, mainly on Sunday night into Monday. Complicated forecast as surface high pressure resides over eastern Canada, keeping cooler air over the region in ESE/SE flow. Model guidance continues to diverge on solutions for the middle of next week with regard to large mid level low. Slightly below temperatures continue throughout the period. && .AVIATION /09Z Thursday THROUGH Monday/... Through 06Z Friday...Mainly VFR conditions across the region with some low to mid clouds holding in at SLK. The VFR conditions still continue through the rest of the overnight hours before trending towards MVFR for northern New York and MPV. Expect snow showers to move into SLK between 10-12z tomorrow as a lake effect snow band will waffle north and south. Due to lack of exact timing I opted to prevail MVFR but I do anticipate periods of IFR in snow showers. The other additional TAF concern is for BTV and MPV as there will be the potential for a snow squall to develop during the afternoon on Thursday. I opted to mention this via a tempo group for the BTV taf between 15-18z. 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 06Z Friday through Monday...After 00z Friday 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. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...Lake Effect Snow Advisory until midnight EST tonight for NYZ029. && $$ SYNOPSIS...Taber NEAR TERM...Deal/Taber SHORT TERM...KGM LONG TERM...KGM AVIATION...Deal/Taber

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