Area Forecast Discussion
Issued by NWS Burlington, VT

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539 FXUS61 KBTV 231926 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 326 PM EDT Fri Sep 23 2016 .SYNOPSIS... Any light showers, mainly across central and southern Vermont will end by late afternoon. Clearing skies will develop from north to south this afternoon and evening as high pressure moves in from Canada. That high pressure system will persist over the North Country through the weekend. Expect below normal temperatures on Saturday and Sunday with highs only in the mid 50s to lower 60s. No precipitation is expected...but the potential will exist for frost in the northern adirondacks and northeast kingdom of vermont, especially early Sunday and Monday mornings. && .NEAR TERM /THROUGH SATURDAY/... As of 220 PM EDT Friday...thicker band of clouds, associated with the mid level front slowly pushing southeast across the region. Radar still showing a few light showers within this band, but as model guidance had suggested, the overall coverage and intensity has been steadily decreasing the last few hours. Still expect a few to hang together this afternoon, so have maintained chance level PoPs for south-central and southern VT. Up north along the border, some sunshine has been breaking through, but with still relatively moist low layers, shallow cumulus clouds quickly form with daytime heating. However, the trend will be for drier air to filter south, and then with sunset even those cumulus clouds will fade away. Temperatures have been tricky, with southern sections already seeing their highs, while across the far north, that little bit of sunshine has allowed temperatures to poke up a degree or two. In general, most everyone is in the 50s, and that is where we`ll stay for the rest of the afternoon. Overnight, high pressure will start to build in, but with the high pressure centered well to our northwest, we`ll continue to have northwest flow advect in cooler and drier air. Eventually the entire region will clear out. Expect that to be early evening across the north and by midnight in the south. A light northerly breeze should continue most of the night, however some of the protected hollows and river valleys should go calm and with the recent rains and warm ground, I would think patchy fog should develop fairly quickly, despite the drier air filtering in. It`s conceiveable that the very coldest spots in the `Dacks and Northeast Kingdom (Saranac Lake NY, Island Pond VT) some patchy frost will also occur. Actually, that`s pretty normal for this time of year. Based on trajectories, the airmass we`ll have tomorrow morning was several hundred miles north of Montreal this morning. Morning lows up in that part of Quebec were in the lower 40s. Thus, the idea of most of us seeing lower 40s for lows (except 30s in higher elevations and colder spots and low 50s right along Lake Champlain) still looks valid. I have made very minimal changes to the low temperature forecast. With the colder air moving in, we`ll probably start to see a little bit of Lake Champlain effect clouds develop late tonight. High pressure will continue to ridge southward over the area on Saturday. Looking like a nearly wall-to-wall sunshiney day, with a few patches of shallow daytime cumulus/strato-cumulus. With temperatures aloft (925mb about 7C and 850mb near 2C), we are looking at temperatures reaching only the lower 60s in the valleys and staying in the 50s at higher elevations. This will give us a rare day of below normal temperatures. Good boundary layer mixing throughout the afternoon, so we`ll probably see some 15-20mph gusts at times. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
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As of 323 PM EDT Friday...Little change from previous couple of days for the near term as we are still expecting the coldest night of the early fall season to occur during this time period. Latest guidance has trended slightly cooler for lows on Sunday night with METSLK showing 19F and 38F at BTV. Synoptic pattern shows building high pres from central Canada with dry northerly flow aloft. Progged 850mb temps drop between 0c to -2c by 12z Sunday with surface high pres axis across the Eastern Great Lakes. This would suggest still some northerly gradient flow...which combined with very warm lake temps...will produce some lake effect clouds and keep temps near the lake slightly warmer. Thinking lows will range from the upper 20s to mid 40s on Sunday morning...with areas of frost in the colder sheltered valleys of the dacks and northeast VT. The upslope flow and leftover boundary layer moisture will produce some fair wx cumulus clouds on Sunday...as temps warm into the upper 40s mtns to near 60f valleys. A chilly night with clear skies and light winds is anticipated for Sunday Night...with widespread frost expected away from the Lake. Thinking lows will range from the l/m 20s to near 40f...depending elevation and closeness to the warm lake waters. Thinking even locations like Williston...Milton and Highgate could experience some patchy frost with a hard freeze likely for the Northeast Kingdom and Dacks.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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As of 323 PM EDT Friday...Guidance has trended toward a more progressive mid/upper level flow across the northern CONUS for next week...which places arrival of precip 12 hours earlier on Monday Night/Tuesday time frame...but good news system lifts out quicker for mid/late week. GFS has trended toward the ECMWF and NAM for an earlier system arrival...so have increased pops to chance after 18z Monday for Saint Lawrence Valley. These pops quickly expand east Monday Night into Tuesday associated with 50 to 70 knot flow at 5h and developing low level jet of 35 to 45 knots. Thinking the initial warm air advection surge will produce a period of showers...with additional rain associated with surface boundary and potent 5h vort on Tuesday. The dynamics look strong with good deep layer moisture advecting ahead of digging mid/upper level trof...so have increased pops to likely for Monday Night/Tuesday. Initial guess on qpf looks to range between 0.25 and 0.75...which is supported by pws around 1.5". Thinking highest pops and qpf values will be in the mountains during this time period. After a chilly start temps will warm into the mid 50s mountains to l/m 60s warmer valleys on Monday with increasing clouds. A warmer night is expected on Monday night associated with precip...clouds...and southerly winds...mainly mid 40s to mid 50s...coldest northeast Kingdom. Midweek...plenty of uncertainty with large scale synoptic pattern...as models show very limited run to run continuity. Given the complex and energized mid/upper level pattern....will continue to mention some terrain focused pops/qpf for Weds...with a drying trend for late Weds into Friday. Both GFS/ECMWF eventually show mid/upper level trof being replaced by building heights and surface high pres. This idea looks reasonable and supported by the latest 12z GFS ensemble data...with developing 1030mb high pressure across the ne conus/mid Atlantic by late week. The combination of upslope flow...lingering 850 to 700mb moisture...and weak low level cold air advection with progged 850mb temps only btwn 0c and 2c...have cut superblend numbers several degrees on weds. Thinking highs mainly mid 50s to l/m 60s...with lows in the upper 30s to upper 40s. A large swing in temps with cooler lows and slightly warmer highs can be expected for Thursday into Friday with deep dry layer in place. Overall...pattern will support near normal temps as we approach next weekend....with dry conditions prevailing.
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&& .AVIATION /20Z Friday THROUGH Wednesday/... Through 18Z Saturday...Conditions run the gamut early this afternoon. IFR all the way to VFR. All thanks to a frontal boundary pushing slowly southeast across the region. Minimal precipitation at this time, and though we`ll have a few more showers in southern VT (mainly the RUT terminal), the precipitation will not result in visibility restrictions. The ceilings are the tough part of the forecast. As the front moves south and the clouds start to dissipate, VFR conditions will develop from north to south. I expect some TAF amendments will be needed as Mother Nature decides to not follow our forecast exactly. Overnight primarily VFR, but there could be some patchy fog with MVFR/IFR developing. Think it`s primarily a MPV and SLK situation, but there is some conflicting guidance for many other locations in the region, so confidence is low on this aspect. After any fog, Saturday will be VFR. Outlook 18z Saturday through Wednesday... 18z Sat through 12z Tue: Mainly VFR. Overnight IFR with patchy fog possible. 12z Tue onward: Potential MVFR with showers. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Evenson NEAR TERM...Nash SHORT TERM...Taber LONG TERM...Taber AVIATION...Nash

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