Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 201952 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 352 PM EDT Sat Aug 20 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH SUNDAY/...
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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.
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&& .SHORT TERM /SUNDAY NIGHT/... As of 420 AM EDT Saturday...Active period of weather expected as vigorous shortwave trough across the central Great Lakes at 12Z Sunday begins to make its way ewd with increasing large-scale forcing across the North Country. A period of moderate to briefly heavy rain is expected later Sunday afternoon into the first half of Sunday night. Attendant cold front across sern Ontario will make its way into nrn NY by 00z Monday, and then sweep eastward across the North Country and east of the CT River Valley by 06Z Monday. Strong sea-level pressure gradient in place Sunday morning across the North Country ahead of frontal system, along with 900mb winds of 30-35kts based on the 00Z NAM. Should translate into widespread southerly surface winds of 15-20 mph, with gusts to 25 mph, and locally 30 mph in the Champlain Valley morning through mid-afternoon. A Lake Wind Advisory will likely be needed (Saturday night into) Sunday based on synoptic setup. Southerly flow in advance of approaching frontal system will rapidly increase PW values, reaching 1.6-1.7" by early afternoon, and around 2" along the cold front late in the afternoon/evening hours. SBCAPE is limited due to lapse rates near moist adiabatic, but values around 500 J/kg should be sufficient for some embedded thunderstorms, producing brief heavy downpours. In terms of timing, appears frontal rainband begins affecting the St. Lawrence Valley 16-18Z, and slowly shifts across the Adirondacks into the Champlain Valley by 21Z. Bulk of rainfall for the Champlain Valley and points east will be between 21-03Z, and then ending from west to east by 06z Mon with strengthening mid-level wswly flow accelerating frontal motion overnight. Will generally see 0.5 to 1.0" rainfall amts, but locally higher with any embedded tstms. That said, motion of cold front appears progressive enough that we should avoid any hydro related problems. High temps Sunday upr 70s to lower 80s with abundant mid-upr clouds followed by rain showers later in the day. Temps cooler quickly later Sunday night with wly wind shift and increasing low-level CAA. Lows generally in the 55-60F range across VT, but lower 50s across NY. && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 420 AM EDT Saturday...Cold front shifts ewd across Maine and off the MA coast Monday morning with trailing mid-upr level trough shifting across the North Country. Moderately strong sfc- 850mb CAA allow 850mb temps to cool to +5 to +6C by 18Z Monday. Strong frontal inversion should preclude any shower activity, but trapped moisture should result in considerable cloud cover through the daylight hours, limiting overall insolational heating. These factors will yield a much cooler day, with highs in the upr 60s to lower 70s in most locations, except some mid 60s at 1-2kft elevations in the Adirondacks and across N-central into nern VT. It will feel much drier with 2-m dewpoints falling into the upr 40s to lower 50s by Monday afternoon. Should see clearing skies Monday night with strong subsidence as broad surface anticyclone builds across the ern half of the CONUS, and becomes centered across central PA/NY during the pre-dawn hours Tuesday. Should set up good radiational cooling, and excellent fog potential in the favored river valleys of central/ern VT, as well as for the valleys within the Adirondack region. Fog may become locally dense after midnight. Overnight lows expected in the low-mid 50s, with a few upper 40s across Essex County VT and vcnty of KSLK in the nrn Adirondacks of NY. Prolonged dry weather expected with high pressure in control through mid-week. Will see a gradual moderation of temperature; mid-upr 70s for Tuesday, and back into the low 80s on Wednesday with mostly clear skies anticipated. As center of anticyclone drifts off the East Coast on Thursday, will see better low-level moisture advection and increase in swly flow aloft across the ern Great Lakes into NY/nrn New England. It appears a few showers/t-storms will be possible with peak daytime heating, mainly across nrn NY, with scattered showers/tstms possible areawide on Friday (PoPs 30-40%) as weak frontal bndry shifts ewd into NY from the Great Lakes. && .AVIATION /20Z Saturday THROUGH Thursday/... Through 18Z Sunday...Generally VFR conditions prevail through this evening, with isolated showers/thunderstorms affecting the St Lawrence valley this afternoon. Southerly winds continue to increase with a few gusts 15-25kts this afternoon. Heading into the evening, showers and thunderstorms diminish with nocturnal cooling with increasing clouds as cold front approaches from the west. MVFR low clouds expected to develop at KMPV, KRUT and KSLK after 06Z. Chance of showers/storms will increase from west to east after 13Z. Winds increase 10-15kts with gusts 15-25kts after 10Z. 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 18Z Sunday through Thursday... 18Z Sunday through 12Z Monday...MVFR with any showers and t-storms. 12Z Monday onward...VFR. && .MARINE...
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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.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Evenson/KGM NEAR TERM...KGM SHORT TERM...Banacos LONG TERM...Banacos AVIATION...KGM MARINE...Verasamy/Evenson

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