Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 220214 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1014 PM EDT Fri Oct 21 2016 .SYNOPSIS... An upper level trough of low pressure is starting become negatively tilted and will continue into early Saturday, keeping frontal boundary and associated surface low pressure system over the region through Saturday night/early Sunday. As the system moves past, colder air will filter in bringing with it northwest flow producing upslope rain and snow showers in higher elevations from early Sunday morning through Tuesday. Another surface low pressure system looks to affect the Northeast Thursday and into Friday. && .NEAR TERM /UNTIL 6 PM SATURDAY EVENING/... As of 1014 PM EDT Friday...Overall forecast in good shape. Only change needed was to add fog to the forecast as fog is fairly widespread across the area and won`t be going away anytime soon. Otherwise...light rain will continue over the area and should increase in areal coverage as upper low takes shape over the area during the day on Saturday. Previous Discussion... Saturday morning, models find more consensus on surface low positioning along the southern New England coast, traversing northward during the day. This means deep NW flow over the North Country will bring in colder air and widespread terrain enhanced rain showers throughout the day and into the early evening. && .SHORT TERM /6 PM SATURDAY EVENING THROUGH SUNDAY NIGHT/... As of 312 PM EDT Friday...Extremely challenging and complex forecast associated with low level thermal profiles and associated snow levels. GFS/NAM/ECMWF and GEM are all in excellent with evolution of negatively tilted and closing off 7h/5h circulation across eastern NY by 21z Saturday and coastal low pressure being captured and becoming vertically stacked over southern Canada by 06z Sunday. This synoptic scale pattern will support a 12 to 18 hour period of favorable deformation and upslope focused precip on Saturday Night into midday Sunday. The difficult question to answer is how cold are the thermal profiles...and associated snow levels. NAM is much colder and faster bring in the colder air...on brisk northwest winds...while GFS/ECMWF are slower and much warmer in the boundary layer to 925mb layer. This makes for a huge difference on impacts associated with snow levels between 1200 and 1500 feet as supported by the NAM or 2000 feet or higher with limited impacts per the GFS/ECMWF solutions. Interesting to note NAM BUFKIT data showing 1.20" qpf falling as all snow...while GFS BUFKIT shows only 0.32". Given the lack of cold air upstream and very warm ground temps from recent warmth...thinking snow will initially have difficulties the mountains towns on Saturday evening. Have noted progged 850mb temp near 0C from KMSS to KBTV to KVSF at 00Z...while the 925mb 0C isotherm is still back northwest of our cwa thru 06z Sunday...supporting snow levels above 2000 feet. Thinking during heavier precip rates...especially on Saturday Night...column will cool enough to support some wet accumulating snow in the mountains towns of the Dacks and portions of the green mountains in VT...mainly above 1500 feet. Have in the grids a dusting to several inches of wet snow for Lake Placid...Tri Lakes Area...Newcomb...and across the higher terrain of central Clinton and Franklin Counties. Given the complex thermal profiles expecting a sharp snow gradient as you climb in elevation with 8 inches or more possible above 4000 feet across the northern Dacks. For the Green Mountains in Vt the colder air arrives first in the central/southern portion...then advects north as closed cyclonic circulations moves northeast. Thinking a similar type scenario plays out with a dusting to several inches of wet snow likely between 1500 and 2000 feet...for towns like Killington...Bread Loaf...Walden...Belvidere...and base area of local ski resorts. Also...expecting a sharp snowfall gradient based on elevation with Mansfield to Jay Peak having the potential of 6 or more inches by Midday Sunday. A few wet snowflakes could mix in at times in the valleys late Saturday Night...but no accumulation is expected. Upslope parameters look very favorable with northwest 925mb to 850mb winds of 35 to 45 knots...strong uvv`s signature across the northern Dacks and western slopes...and plenty of 850 to 700mb backside moisture. Thinking additional qpf values will range from 0.05 to 0.15 Saint Lawrence and Lower CT River Valley with near 0.50 eastern CPV/parts of the Northeast...and up to 1.0 northern Dacks and parts of the central/northern Green Mountains from Mansfield to Jay Peak. Next concern will be developing winds associated with tightening pressure gradient with 979mb low pres. Soundings show strong low level wind fields of 40 to 50 knots...with bottom of the mixed layer winds around 35 to 40 knots Sat Night into Sunday. Still some questions how much mixing occurs with precip and clouds...but thinking as drier air develops on Sunday...surface wind gusts between 35 and 45 mph will be possible...with even higher gusts on exposed mountain summits. For people adventuring out to experience the first snow of the season in the mountains...please be prepared for mid winter conditions on Sunday...especially near the summits. Temps will range from the mid/upper 20s mountains to upper 30s/lower 40s warmer valley locations near Lake Champlain on Saturday night and only warm 3 to 5 degrees on Sunday with brisk northwest winds. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 315 PM EDT Friday...After a prolonged warmer than normal period through the summer and into the first 20 days of October...a prolonged period of BELOW normal temperatures are in store for the north country...Fall is here! This weekends cut-off low will still strongly influence our weather through Tuesday. The cut-off lifts into Quebec but the cool, cyclonic and marginally unstable flow will persist through Tuesday with the typical climo-favored upslope rain/snow showers but less than the weekend. Still cyclonic flow in trof pattern but lessening influence by Wednesday with Surface high moving into region for dry day but still cool. Another shortwave moves into the trof with a surface low and warm front for Thu and possibly Fri which brings back more inclement weather but not like this last system. Some mountain rain/snow but timing later thursday should keep just rain for valleys. Highs in the 40s through Thursday and back to seasonable L50s by Friday. && .AVIATION /02Z Saturday THROUGH Wednesday/... Through 00z Sunday...Significant impact to aviation through the TAF period mainly from OVC MVFR to LIFR ceilings and related mountain obscuration. Ceilings likely to oscillate between these three flight categories but will predominate as IFR. Rain showers interspersed with a 1-3 SM mist continue to spread northward affecting SLK, MSS, and MPV, with a break in steadier rainfall in the Champlain Valley. These trends likely to continue through most of the overnight. However, axis of steadiest rain axis then begins to pivot from southwest to northeast during the day on Saturday, resulting in a more widespread 4-6 SM rain across the TAFs. Northwest winds 4-8 kts tonight, increasing in speeds to 8-12 kts on Saturday. Outlook 00z Sunday through Tuesday... 00z Sunday through 00z Monday: A prolonged period of unsettled conditions is expected with widespread MVFR/IFR in periods of rain. 00z Monday through 00z Wednesday: A mix of VFR/MVFR with upslope showers in NW flow. && .HYDROLOGY... As of 315 PM EDT Friday...Through early this afternoon the heaviest rainfall has been located over the Saint Lawrence Valley and Northern Dacks (1 to 3.5 inches)...the amounts tapering off sharply with < 0.75 inch across the central/southern Champlain Valley and most of VT. Moving forward thinking additional rainfall will range between 1 and 2 inches with some isolated higher amounts along the western dacks possible. Several periods of rain still anticipated for system tracks along the coast and Atlantic moisture is advected back into the region tonight. Given the long duration and breaks in the precip intensity/coverage...we are not anticipating any hydro related issues associated with this event. However...some minor urban and street flooding is possible associated with the heavier rainfall rates through Saturday with leaves clogging storm drains. Otherwise...some modest rises in local rivers and streams are likely this weekend...but no widespread flooding is anticipated. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...MV NEAR TERM...Evenson/MV SHORT TERM...Taber LONG TERM...SLW AVIATION...Loconto/SLW HYDROLOGY...Taber is the U.S. government's official web portal to all federal, state and local government web resources and services.