Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 241440 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1040 AM EDT Mon Jul 24 2017 .SYNOPSIS... Upper low pressure will cross the area today into tonight with widespread rainfall and cool temperatures before exiting east on Tuesday. High pressure brings a brief stretch of fair weather on Wednesday before a weak cold front brings a renewed threat of showers and storms on Thursday. Fair weather then returns for Friday into next weekend with temperatures near seasonal late summer norms. && .NEAR TERM /THROUGH TUESDAY/...
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As of 1010 AM EDT Monday...no substantial changes for the mid- morning update. Folded in latest satellite, temperature and radar trends. Like how the HRRR and BTV4 WRF model are handling the "now", so blended in their output for the next 6 to 12 hours as well. Issue the next few hours will be threat for additional flooding in southern parts of St Lawrence County. Radar estimates indicate a few locations in excess of 6" since 1am this morning within a 40 mile long/10 mile wide east-west oriented heavy rainfall footprint. This seems quite reasonable given 5.65" measured at the NY State Mesonet site in Hammond as of 1005am, and a few other mesonet sites in the area showing almost 4". Still have another round of moderate to briefly heavy rain approaching the southern parts of St Lawrence Valley as I type with rainfall rates about 0.2 to 0.4" per hour. Lightning data show electrical activity with that convection, though most of the lightning is just south of the region that has had the most rain. Hopefully it stays that way. All of this precip is thanks to a vigorous shortwave embedded in a negatively tilted trough swinging across the eastern Great Lakes right now. GOES-16 mid-level water vapor shows that shortwave very nicely. That puts our region on the eastern diffluent side of that trough. That shortwave will be reaching the St Lawrence Valley mid-afternoon. Expect that as happens, chances for heavy rain will start to diminish as drier air aloft moves in. Precipitable water values fall to <1.0" with and behind that trough, compared to the current 1.5" across the region per latest GPS-Precipitable Water measurements in Burlington, Plattsburgh and Watertown. Clouds and precipitation will keep temperatures pretty much steady where they are. With moist east/southeast flow, did knock highs down a few degrees, especially eastern Vermont. Chances of thunder seem minimal for this afternoon. All models indicate the weak surface based and instability aloft will remain from the southern St Lawrence County and extend south. As such, have kept slight chance of thunder only for southern parts of St Lawrence, Franklin and Essex Counties in NY. Those are also the areas at most risk for locally heavy rainfall for the next few hours. Don`t mean to ignore Vermont. For the most part, it will be on and off light to occasionally moderate showers all day. With east/southeast flow, there is a little bit of downsloping along western slopes of the Green Mountains. Max gusts I`ve seen have been 25-30 mph. Don`t anticipate anything more than that since there is only 25 knots or so at 850mb. Prior discussion from the midnight shift forecaster for tonight and Tuesday... By tonight showers will remain quite abundant in coverage, though wane in overall intensity as the system continues to pivot slowly east. Patchy br/fog also a good bet just about anywhere as temperatures hold in the 50s. Winds light. On Tuesday widespread morning showers gradually move east and/or fade away as longwave trough exits east and building high pressure advances east from the Great Lakes and Ohio Valley. Plenty of clouds should be the rule most of the day, though some partial sunshine will be possible from the Champlain Valley west by later in the afternoon. Temperatures remain on the cool side in the 60s, possibly touching the 70F mark in the SLV where partial sun may arrive a bit earlier than other areas.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/... As of 333 AM EDT Monday...Dry weather will persist Tuesday night and Wednesday with upper level and surface ridging over the area. Decreasing cloud cover Tuesday night will set us up for some fog formation, locally dense, from 06-12z. Surface high crests over the region on Wednesday, with warm southwesterly flow developing. Cooler than normal temperatures Tuesday night, mainly 50s with some 40s in the Dacks. Temps rebound nicely on Wednesday with near seasonal normals expected, upper 70s to around 80. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 333 AM EDT Monday...All of the weather in the long term will be in the first few periods, mainly Wednesday night and Thursday. A cold front will push across the region with showers and perhaps thunderstorms Thursday afternoon. This will depend a lot on the timing of the front which will become more clear as we get closer to Thursday. Have mentioned likely pops for Thursday, because this looks like the time period when the fropa will happen. Showers should be ending during the first part of Thursday night, though Euro does depict a slower system. Right now the Friday through Sunday timeframe looks quiet with large ridge of surface high pressure over the region. Temperatures will be near normal through the week. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... Through 12Z Tuesday...Deteriorating conditions expected across the area today into tonight as upper low pressure brings widespread rainfall to the region. Thunder threat rather low and confined to northern New York counties. Lack of expected coverage warrants omission from NY terminal forecasts at this point. Generally looking at VFR trending MVFR at all terminals in the 09-18Z time frame as rain arrives from southwest to northeast. Exception at KSLK where patchy IFR stratus will linger a few hours this morning before trending MVFR. Brief IFR visibilities possible in heavier showers, especially in northern NY. Showers trend a bit lighter after 00Z Tuesday, though scattered coverage remains across the area as cigs lower into the 005-015 AGL range (IFR/MVFR) with widespread 3-5sm br and localized areas below 2sm. Winds east to southeasterly through the mainly in the 5 to 15 knot range, though occasionally gusty to 30 kts at KRUT in the 12-00Z time frame, trending light after 00Z. Outlook... Tuesday: VFR. Chance SHRA...Patchy morning FG. Tuesday Night: VFR. Patchy dense FG. Wednesday: VFR. Wednesday Night: VFR. Slight Chance SHRA. Thursday: VFR/MVFR. Likely SHRA...Chance TSRA. Thursday Night: VFR. Chance SHRA. Friday: VFR/MVFR. Slight Chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...JMG NEAR TERM...JMG/Nash SHORT TERM...Neiles LONG TERM...Neiles AVIATION...JMG

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