Area Forecast Discussion
Issued by NWS Burlington, VT

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136 FXUS61 KBTV 241127 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 727 AM EDT Sat Sep 24 2016 .SYNOPSIS... A high pressure system moving down from Canada will bring dry weather to the area this weekend. Expect plenty of sunshine and no precipitation along with below normal temperatures. Highs will only be in the mid 50s to lower 60s. More importantly...low temperatures tonight and Sunday night will get cold enough for frost to develop over the Northern Adirondacks of New York...the west slopes of the Green Mountains...and north central and northeast Vermont. && .NEAR TERM /THROUGH SUNDAY/... As of 643 AM EDT Saturday...Updated forecast to mention dense fog everywhere across northern New York and Vermont this morning rather than confining it to the favored locations. Much of the area has visibilities under a mile with quite a few spots near zero. Have gone ahead and issued a Special Weather Statement to emphasize the potential impacts of the fog on travel. Remainder of forecast in good shape. Frost Advisory in effect from 2AM to 8AM Sunday for the Northern Adirondacks of New York...the west slopes of the Green Mountains in Vermont...and north central and northeast Vermont. Temperatures will fall into the lower to mid 30s across this area...which should be sufficiently cold to develop frost and potentially have an impact on vegetation sensitive to cold temperatures. Otherwise...looking at quiet weather today through Sunday with high pressure building down from Canada. We`ll have fog early this morning...but will burn off by mid-morning. Plenty of sunshine today and Sunday...but cold air advection will lead to below normal temperatures with highs generally in the mid 50s to lower 60s both days. Steepening lapse rates by midday will lead to better mixing and northwest winds will pick up in the 10 to 20 mph range before gradually tapering off after sunset. There may be enough wind in the mountains overnight to limit the areal coverage of frost at the highest elevations...but temperatures will definitely be cold enough. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/... As of 451 AM EDT Saturday...Biggest challenge in the short term period is how low will the temperatures go Sunday night. Very good setup for radiational cooling as surface ridge moves across the forecast area for near calm winds. Low RH, below 30 percent in the 1000-500 mb layer, will produce cloud free skies. Superblend was several degrees warmer this run that previous official forecast, apparently the raw model output used in the consensus group is not handling the radiational cooling very well. Additionally the bias applied will be based on past day`s warm bias, but now that we`re in a cooler than normal regime will take a day or two for that to catch up. So bottom line have adjusted superblend heavily back toward previous forecast. This results in area of below freezing in the Adirondack portions of St. Lawrence, Franklin, Clinton, and Essex Counties NY and Essex County VT. Frost producing temps 33-36 possible over much of the remaining area except areas close to Lake Champlain where warmer waters moderate temperatures. If this forecast holds will need Freeze Warning for Adirondacks and Northeast Kingdom, and Frost Advisory elsewhere. On Monday the surface ridge will shift east, allowing light southerly flow to begin. Rising heights and low level warm air advection will bring 850 mb temps from a couple degrees below zero Sunday night +5 in northeast VT to +9 northern NY by Monday afternoon. This will yield temps a little higher than blend of models offers, so nudged gridded max temps upward based on 850 mb temp reduction. Otherwise sunny skies for much of the day, then high clouds move in from west to east late in advance of approaching low from the west. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 451 AM EDT Saturday...Guidance still in agreement that we saw come together yesterday with upper low driving through Great Lakes into the forecast area, and slowly moving across the region through mid week. At the surface a frontal system will move through Monday night and Tuesday, with a narrow band of showers along the front. Good upper level support with this feature with diffluent flow on the east side of the 500 and 300 mb low, and a 45 knot 850 mb southerly jet translating west to east Monday night across northern NY and Vermont. Moisture feed with this is impressive for this time of year with Precipitable Water around 1.3 inches according to the GFS, which puts it in the 90th percentile. Despite moisture feed and dynamics producing 75 knots of 0-6 km shear, temps remain much too cool to support any instability that would produce thunder, and kept precip type as just showers. Expect a scenario where showers along the surface front will move west to east Monday night and Tuesday. Upper low then settles in over the eastern US for continued chances for showers under the cold pool aloft, aided by westerly low level upslope flow. The upper low will slowly move east and fill, with low level ridging moving in, and decrease POPs through chance category Tuesday night and Wednesday, with a dry forecast from Wednesday night onward. After the initial warmup at the start of the extended period there will be little airmass change. Temperatures will trend near normal with highs in the 60s and lows in the 40s. && .AVIATION /11Z Saturday THROUGH Wednesday/... Through 12Z Sunday...IFR to VLIFR conditions will exist through 13z or 14z at all locations due to low clouds and fog with the exception of KPBG where no fog exists. Once the fog burns off VFR conditions will exist everywhere for much of the remainder of the period as no clouds are expected. After 08z there may be some brief periods of IFR at KSLK and KMPV due to fog and low clouds forming. Light winds will become northwest after 14z with speeds increasing into the 10-15 knot range...then taper off after 00z. Outlook 12z Sunday through Wednesday... 12z Sun through 12z Tue: Mainly VFR. Overnight IFR with patchy fog possible. 12z Tue onward: Potential MVFR with showers. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Frost Advisory from 2 AM to 8 AM EDT Sunday for VTZ003-004- 006>008-010-016>019. NY...Frost Advisory from 2 AM to 8 AM EDT Sunday for NYZ029>031-034. && $$ SYNOPSIS...Evenson NEAR TERM...Evenson SHORT TERM...Hanson LONG TERM...Hanson AVIATION...Evenson/Nash

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