Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 110243 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 943 PM EST Sat Dec 10 2016 .SYNOPSIS... A cloudy and chilly evening is expected as high pressure crests over the North Country. The coldest air of the season will see lows overnight dropping into the single digits for most of the eastern Vermont and Adirondacks with teens expected for the Champlain and Saint Lawrence Valleys. The Monday morning commute is expected to be significantly impacted as our next system arrives on Sunday Night into Monday with a widespread accumulating snowfall expected. Total snow accumulations will range from 3 to 7 inches by Monday afternoon. && .NEAR TERM /UNTIL 6 PM SUNDAY EVENING/...
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As of 943 PM EST Saturday...Additional updates needed late this evening to the temperature forecast as high pressure building in providing clearing skies and light winds is combining with a shallow snowpack to plummet lows well into the single digits outside of the deeper valleys. Coldest spot is Island Pond Airport sitting at a lovely -4F, with Adirondack Airport in Saranac Lake not too far behind at -1F. Since no guidance has a clue on how low temps will go, used my best judgment based on the cloud forecast to indicate temps falling a few degrees more below current readings through the remainder of the night. This yields -5F to -10F in the Adirondacks and Northeast Kingdom, to low teens in the deeper Champlain and St. Lawrence Valleys, and 0-10F elsewhere. The high slowly begins to drift east Sunday morning and so the synoptic flow turns more southerly and the clouds will break by mid morning. This will also shift the lake effect snow band over Lake Ontario back up towards the north and should see at least some light snow developing over southern Saint Lawrence County mid morning. Through Sunday afternoon expect partly cloudy skies to increase and thicken as a low pressure system begins to lift north. Latest runs of the hires guidance show the warm air advection precip moving in even faster than the previous couple of days and so by 21z expect light snow showers to already be falling over the Saint Lawrence valley. The precip should quickly overspread the rest of the North Country due to a strong low level jet developing Monday evening.
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&& .SHORT TERM /6 PM SUNDAY EVENING THROUGH MONDAY NIGHT/... As of 245 PM EST Saturday...An active period of weather still on track to affect the region Sunday night into Monday with widespread accumulating snows. Latest model data continues to support the idea that Great Lakes low pressure will track east and drive an occluding warm front across our area during this time frame with modestly robust isentropic lift and moisture advection being the primary driver for precipitation. Current thinking maintains consistency with prior forecasts offering a widespread 3-7 inch snowfall by late morning/early afternoon on Monday, and given this consensus have issued Winter Weather Advisories for the area Sunday evening into the first half of Monday accordingly. Slight snowfall variation due to shadowing/upslope effects will also be possible given mean 925-850 mb flow will hover from 150-170 degrees at 30-50 kts during the core of the event. Thus local enhancement along the eastern faces of the southern Green Mountains looks plausible with slightly lesser totals along leeward/western facing mountain slopes. However, given depth of moisture and dynamical forcing feel overall uniformity in snowfall distribution will be on the higher side. By Monday afternoon consensus remains high that as the primary low tracks north of our area we`ll enter a pronounced dry slot with precipitation trending more scattered and lighter over time. With mid to upper levels trending unsaturated some patchy light rain, drizzle or even freezing drizzle will be possible across portions of the area as temperatures climb near or slightly above the 32F mark. Any light freezing drizzle that would occur seems most likely across our southern VT counties east of the Greens. However, given the lighter character of the afternoon precipitation any icing threat should be minimal. In terms of temperatures I did base max/min values off 3- hourly hi-res/bias-corrected data showing readings trending steady or slowly climbing Sunday night, topping out in the 30s on Monday. By Monday night parent cold front sweeps through the area with background flow trending westerly over time and lingering snow shower activity becoming more confined to the northern mountains as orographical processes begin to dominate. Lows holding fairly mild however - generally 20s to locally around 30 in the Champlain Valley. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 245 PM EST Saturday...Subtle changes exist in this morning`s global models for the middle to later portions of next week, though by and large the overall idea of a trend toward much colder weather with scattered flurries/snow showers still appears reasonable at this point. Main player will be a large- scale cyclonic polar gyre that will drop across southern Canada during late week and force a pronounced arctic boundary through the area on Thursday. Enhanced snow shower activity likely to get going in the Lake Ontario snowbelts on Wednesday as west/southwest flow continues in earnest ahead of the boundary, with activity sweeping through Vermont by Wednesday night along the front. Some minor accumulations certainly possible here, with slightly heavier totals in the snowbelts. Behind this boundary the coldest airmass of the season will arrive with some preliminary data suggesting at least the possibility of lower wind chills on Thursday night. Highs start the period mild (30s) on Tuesday, cooling into the 20s by Wednesday, 10 to 20 on Thursday and upper single digits to teens on Friday. Lows follow suit with the coldest readings occurring Thursday night and Friday night when readings fall into the positive/negative single digits. By next weekend, broad consensus continues showing our next system of midwestern origin will take a Great Lakes/St. Lawrence Valley storm track with a renewed threat of more widespread precipitation and temperatures moderating back toward more typical mid- December values. && .AVIATION /03Z Sunday THROUGH Thursday/... Through 00z Monday...Outside of some lingering MVFR cigs across the Adirondacks and north/central Vermont, VFR conditions will largely rule through the next 24 hours with a gradual clearing trend to near SKC after midnight. Mid clouds increase beginning mid-day tomorrow from the southwest in advance of our system. Light winds tonight trend south/southwest 5-10kts tomorrow. Outlook 00z Monday through Wednesday... 00z Monday - 00z Tuesday: MVFR and IFR as a warm front brings snow showers to the area, heavy at times, with some light icing during the afternoon Monday. Low level turbulence will be possible as a low level jet brings 35-45kts winds just off the surface. 00z Tuesday - Wednesday: Continued periods of VFR/MVFR in scattered snow showers are possible Tuesday into Weds with brief IFR possible. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Weather Advisory from 7 PM Sunday to 1 PM EST Monday for VTZ001>012-016>019. NY...Winter Weather Advisory from 4 PM Sunday to 10 AM EST Monday for NYZ026>031-034-035-087. && $$ SYNOPSIS...Deal NEAR TERM...Deal/Lahiff SHORT TERM...JMG LONG TERM...JMG AVIATION...Deal/Lahiff

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