Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 202335 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 735 PM EDT Sat Aug 20 2016 .SYNOPSIS... A few isolated showers and thunderstorms will continue to across the Saint Lawrence Valley of New York this afternoon before diminishing late this evening. Sunday, a low pressure will drag a cold front across the region bringing widespread showers and storms to the entire area...especially in the afternoon and night. High pressure returns bringing cooler temperatures and drier weather. && .NEAR TERM /THROUGH SUNDAY/... As of 352 PM EDT Saturday...Isolated showers and thunderstorms will continue across the St Lawrence valley this afternoon and evening as instability remains significant through the daytime. As the sun sets and nocturnal cooling starts to settle in, instability will decrease and convective activity will diminish. With the night starting mostly clear, few areas of patchy fog especially where rain occurs will be possible early in the night. A low level south to southwest jet will move into the region overnight along with tightening pressure gradient head of approaching low pressure system. Expect winds to mix with some gusts developing late tonight/early Sunday morning, especially in the St Lawrence Valley. With increasing clouds and winds, expect temperatures to remain mild with morning lows ranging from around 60 to low 70s. Cooler areas will be in the Northeast Kingdom as this area is more removed from clouds (spreading west to east) and low level jet may not reach this area til sunrise. Generally expect precip ahead of low and associated cold front to hold off til about 12Z, before spreading west to east, reaching the Champlain Valley around mid day. With PWATs 1.5-2 inches, showers and thunderstorms could produce periods of moderate to heavy rainfall. Strong deformation zone will move into the region 18z into the early evening, which will help provide focus for showers/storms and heavier rainfall. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 356 PM EDT Saturday...Short term period picks up 00z Monday with band of rain forecast to be mainly in Vermont and surface cold front entering the St. Lawrence Valley. Bulk of precip out of the area by 06z Monday with lingering showers in Northeast Kingdom until 12z Monday. Winds turn northwesterly behind the cold front and temperatures begin to fall. Best cooling in the northern NY portion of the forecast area with lows into the 50s. Vermont will just be feeling the effects of the cold front by the time we draw the line for overnight lows at 12z Monday, so lows will be limited to upper 50s to lower 60s. By 12z Monday the surface front moves off the New England coast. Cold air advection makes itself felt on Monday with daytime temps struggling to recover against 850 mb temps dropping 10 degrees in 12 hours from 03z-15z Monday. As noted by mid-shift forecast limited sunshine as well with moisture trapped by a strong frontal inversion resulting in considerable cloud cover through the daylight hours, limiting overall insolational heating. Base of 500mb trough centers over the Champlain Valley around 15z on Monday then moves quickly on east. As a result Monday the coolest day of the week with highs mostly in the 60s. High pressure builds at the surface with rising heights and plenty of sunshine in low RH air early in the week, and a broad 500 mb ridge sets up along the eastern seaboard with warmer southwesterly flow developing. A warming trend through midweek, and temperatures rebound to the 70s Tuesday. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 356 PM EDT Saturday...By Wednesday the surface and upper ridge are forecast to be east of the area with trough over the central US. Southerly boundary layer flow and southwesterly mid and upper level flow returning moisture and reinforcing the warmer air. Not terribly hot with highs in the 80s but dewpoints creep back up into the 60s by the end of the week. Thursday into Friday a southwest to northeast oriented cold front slowly pushes eastward out of the Great Lakes. Gridded model guidance for Probability of Precip performed poorly Thursday, with our blend of models bringing high chance pops in Thursday afternoon. This is well ahead of the arrival of the surface boundary and upper dynamics, with the region still under the influence of the nearby ridge. GFS BUFKIT soundings that far out show no instability to support pre-frontal convection. As a result scaled back Superblend POPs significantly through Thursday night, blending in a healthy dose of straight MOS guidance to bring POPs back down. Allowed pops to increase Thursday night to Chance category by Friday morning and remain at chance during the day Friday with the frontal passage. Still out pretty far to try timing things on days 6 & 7, but expect it to be similar to tomorrow`s cold front and move through pretty quickly. Temperatures Friday a little cooler in the upper 70s/lower 80s with clouds and rain, and generally in the 70s Saturday. && .AVIATION /23Z Saturday THROUGH Thursday/...
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Through 00Z Monday...VFR through the overnight and a large part of Sunday, trending VFR/MVFR 18-00z Monday. Skies should trend mostly clear across the St. Lawrence Valley. Short- range and LAMP guidance continues to show MPV getting some MVFR stratus, and while that can happen on prevailing SSE/SE flow current satellite reveals no such lower ceilings around. Started to trend more optimistically with ceilings. Appears that winds will also be too strong to support any fog development tonight despite otherwise favorable conditions. South winds 6-10 kts tonight. VFR with lowering ceilings west-to-east and gusty south winds for Sunday. Ceilings to lower to VFR/MVFR with the front with a timing from 18-00z. MVFR moderate showers/thunderstorms expected primarily along the frontal zone. By 00z Mon, front should be near the Champlain Valley. Winds south 10-12 kts gusts up to 25 kts. NOTE: Rutland AWOS (RUT) is not operating. Because of the lack of disseminated observations, we continue our suspension of amendments for the RUT TAF. Once the communication problem has been resolved, and we again get routine observations automatically transmitted, we will lift that restriction. Outlook 00Z Monday through Thursday... 00Z Monday through 12Z Monday...MVFR with any showers and t-storms. 12Z Monday onward...VFR.
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&& .MARINE... As of 320 PM EDT Saturday...Southerly winds are increasing this afternoon (10 to 20 knots) and expected to continue to do so through tonight. The winds will reach peak strength by Sunday afternoon, with winds frequently reaching 30 knots, especially across the open areas of the broad lake. Some gusts are expected to approach 35 knots. Additionally, showers and a few thunderstorms are expected to develop during the afternoon hours on Sunday and continue into Sunday night. Those planning on boating this weekend, especially Sunday, should pay close attention to the forecast. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Evenson/KGM NEAR TERM...KGM SHORT TERM...Hanson LONG TERM...Hanson AVIATION...KGM/Loconto MARINE...Verasamy/Evenson

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