Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 221910 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 310 PM EDT Fri Jul 22 2016 .SYNOPSIS... scattered showers and thunderstorms, some possibly severe, are expected through Saturday as a frontal system moves slowly through the region but there will be partly sunny rain free periods as well. It will be hot today with high temperatures in the mid 80s to lower 90s. Another round of thunderstorms is possible on Monday. Meanwhile Sunday looks dry and seasonable. && .NEAR TERM /UNTIL 11 PM THIS EVENING/... As of 1245 PM EDT Friday...At 1pm already 90F here at BTV and likely getting into L90s if not a few degrees higher. In Vicinity where SFC heating should be able to break CAP. SFC based CAPES already 1000-2000 J/KG across much of the area. We have a pre-fntl trof moving through but no fanfare as it moves across slightly more stable VT. A cluster of storms is developing in Quebec with the main track toward Maine later today/tonight. All guidance suggests something trying to get going between 4-7 pm and still believe that will happen but most of the activity tonight should be nrn VT. No changes exept bumping temps up a notch in a few locales. Previous Discussion...Dry Air aloft had developed a CAP and basically awaiting some trigger. VSB satellite showing linear feature which looking at model data I attribute it too mid-lvl trof and pre-fntl trof. Although we and high resolution models have backed off for any thunderstorm show to begin after 4 pm and come from quebec...will still need to watch closer to home for early afternoon. Confidence is low as High RES models have not handled well. No changes to current forecast. Previous Discussion issued at 751 am...The shortwave and scattered early morning showers/storms have exited the area and some shortwave ridging is resulting in some temporary stabilization. Model soundings mix down decent dry air advection that should allow for plenty of sun to develop and thus heat up for high temperatures reaching the mid 80s to lower 90s especially where westerly to southwest winds downslope into the valleys. Surface instability should start to return this afternoon but will depend on how much dry air gets mixed down to the surface and what the resulting dew points are. Right now it looks like low to mid 60s should do it which will give us CAPES around 1000 J/kg, some of the models suggest dew points will be peaking into the upper 60s later in the day when CAPE may rise to 1500 to 2000 J/kg. It will probably end up somewhere in between. Very dry mid-levels support downward momentum for potentially damaging winds and hail given wet bulb zero levels drop below 10K. 0-6km shear values are around 40 kts which also support the severe potential. SPC outlook has us in the slight chance category for today. The main trigger for thunderstorms should be toward late afternoon and evening hours. Low level instability still prevalent early and area in closer proximity to approaching stronger nrn stream shortwave...surface front as well as nose of 300mb and 500mb jets moving into area by 00z Sat enhancing any lift. Tonight...Any shower/thunderstorm activity wanes after midnight but still influenced by northwest cyclonic flow which will keep shower threat especially across NC-NE Vermont. Could be some patchy fog around especially where it rains this evening. lows mainly in the 60s. && .SHORT TERM /11 PM THIS EVENING THROUGH SUNDAY NIGHT/...
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As of 310 PM EDT Friday...Scattered showers/storms (a few possibly strong early) then wane and exit east fairly quickly Saturday evening as upper trough swings through the region and is replaced by building high pressure. Will carry 30/40 pops through about 900 pm or so to account for timing uncertainties, then trend conditions largely dry from midnight onward. Low temperatures near seasonal mid-summer norms in the 50s to around 60 for most locales. Ideal weather then expected by this coming Sunday with surface high pressure bridged by dry and zonal westerly flow aloft. Mean 925-850 mb thermal profiles support highs in the 77 to 83 degree range under light west to northwesterly winds and ample sun. This definitely will be the better day of the two weekend days. By Sunday night our next shortwave trough in the pipeline begins to approach from the Great Lakes with mid to high level cloudiness advecting into the region later at night as flow backs to southwesterly and warm thermal advective processes begin aloft. There could be a stray shower or isolated storm in developing mid- level instability as lapse rates aloft steepen and heights begin to fall, but drier air in lower levels should preclude anything widespread. Will carry a nominal 20/30 pop across our western counties to account for any activity that may occur. Low temperatures a blend of available guidance supporting values generally in the 55 to 65 degree range.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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As of 310 PM EDT Friday...The shortwave trough then swings quickly through the area Monday into Monday evening with a good threat of showers and storms. Some parameters support a few stronger storms but early indications suggest plenty of mid/high level moisture around that could limit boundary layer destabilization ahead of the associated surface trough. Time will tell how this all pans out. For now have maintained continuity offering solid pops in the 40-60 percent range. Temperatures should average slightly above seasonal levels with highs in the 80s and lows Monday night in the 60s. Behind this system our typical mid-summer pattern continues with the region largely on the south edge of the westerlies and deeper heat and humidity off to our south and west. Temperatures should average slightly above seasonal levels with daily highs generally in the 80s and overnight lows in the 55 to 65 degree range. Additional shortwave energy riding through the mean flow may affect the area by next Thursday or so, but timing and strength differences in this morning`s global models support capping pops below 40 percent at this point.
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&& .AVIATION /19Z Friday THROUGH Wednesday/... Through 18z Saturday...mainly VFR and expecting another possible round of showers/thunderstorms in the late afternoon or evening with another upper level short wave and surface trough, again producing mvfr vis in scattered rain showers perhaps some very brief IFR in thunderstorms. These storm coincide with daytime heating and may produce strong gusty winds and hail. Best guess is northern NY and VT in the 21-03Z period. Showers and storms will wind down by midnight. Some patchy fog or mist possible where it rains, but for now just put in at MPV where climatology favors it. South to southwest winds will be 10-15G23KT today, perhaps veering more to west later this afternoon and diminishing tonight. Aft 12z Sat...VFR, with scattered brief MVFR/IFR in showers and thunderstorms. Some thunderstorms may contain strong winds and hail. Outlook 18z Saturday through Tuesday... Sat...VFR, with scattered brief MVFR/IFR in showers and thunderstorms. Some thunderstorms may contain strong winds and hail. Sun...Mainly VFR under weak high pressure. Mon/Monday night...VFR with scattered brief MVFR/IFR in showers and thunderstorms with frontal passage. Tuesday...VFR/high pressure. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Sisson NEAR TERM...Sisson/SLW SHORT TERM...JMG LONG TERM...JMG AVIATION...Sisson/SLW

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