Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 191945 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 345 PM EDT Sat Aug 19 2017 .SYNOPSIS... A trough of low pressure will move through northern New York and New England tonight. The threat for isolated showers will continue through late evening, then taper off with the arrival of drier air after midnight. High pressure will build in for Sunday and Monday, with favorable conditions to view the eclipse on Monday. Temperatures will be seasonably warm, with highs Sunday in the mid 70s to lower 80s, and into the 80s for Monday. Overnight lows will be in the upper 50s and 60s. Another low pressure system will renew chances for showers and thunderstorms Tuesday and Wednesday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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As of 342 PM EDT Saturday...Isolated showers continue but are shifting more into northern VT at late afternoon. Will continue to move east with slight chances continuing through the evening as long as instability remains ahead of the approaching trough. Partly/mostly cloudy through the evening with temperatures slowly falling. 500 mb trough will sweep west to east through the region tonight. Surface trough follows along, and while not big airmass change for cooling temperatues a westerly wind component will advect drier air into the forecast area. Isolated showers possible mainly before midnight and in northeast Vermont in lingering low level moisture and as upper trough passes. Surface dewpoints will fall from mid 60s into the 50s from west to east overnight. Still quite a bit of cloud cover tonight, and along with dewpoints will limit cooling of overnight lows to 55-65 degrees.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/... As of 340 PM EDT Saturday...Brief 500 mb shortwave ridging Sunday night, otherwise upper flow is predominately zonal westerly. A surface high centered over PA on Sunday will move to off the Delmarva coast by Monday, with surface ridging nosing north into New England. Quiet weather will result, although building heights and more sunshine will warm temperatures a few degrees each day. Highs Sunday 75 to 85, while Monday will be solidly in the 80s. 850 mb and 925 mb temps support 87 at KBTV on Monday. Increase in humidity Monday as the surface ridge shifts east and return flow brings surface dewpoints well into the 60s especially in the St. Lawrence valley. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... As of 340 PM EDT Saturday...pretty decent agreement with the 12z suite of models for the week. Generally letting the model blend ride, especially for Wednesday onward. No big changes to the overall scenario expected, though some of the details - especially for Tuesday -- appear to becoming a bit more clear. The models have shifting back a little faster such that we have better timing with the combo of strong dynamics and instability with peak afternoon heating, suggesting an increased chance of organized strong convection and locally heavy rains late Tuesday. Still rather far out in time to lock down any specific details, but some of the model guidance did catch my attention. For the daily details, keep on reading. Monday night: For most of the region, it will be quiet -- however can`t rule out an isolated shower out across the St Lawrence Valley and close to the Canadian border. This is from the initial surge of moisture that will be moving across the region in a deepening southwest flow. Dewpoints will also start to increase overnight, so a little muggy feeling. Tuesday/Tuesday Night: This is the time period the latest model runs are now focussing in. Potentially a very active 12-18 hours. Upper trough will be moving into the Great Lakes, and promote the development of a fairly deep surface low for this time of the year (sub 1000mb). Potent system will also have a pretty strong low/mid level jet, with 850mb winds 40-50 knots, which will be spreading into northern NY by afternoon. All the models show pretty solid amount of instability, with the NAM the most unstable (probably too high with dewpoints). There is some question as to how much sun we`ll see, which will also have an impact on high temperatures and instability, but bottom line we`ll have instability and strong dynamics in place. Noted that SPC had shown a day 4 slight risk just southwest of our region, but that was based on the 00z models, which were a little slower in timing. Also noted a good slug of moisture with this system, with precipitable water values nearing 2.0". That suggests locally heavy rainfall is a good bet as well, and based on some model signals, rainfall totals over 1 inch will probably occur. Bottom line, we`ll have to keep watch for how later model runs trend. Could be a busy weather day/evening with strong/severe t-storms and locally heavy rain. As they say on TV, "Stay Tuned for later updates". Wednesday: Based on the 12z guidance timing, looks like residual showers will be around in the morning and diminishing by afternoon as the surface front moves through. Given some uncertainity in model trends, have kept in a fairly wide timeframe for the chance of showers, though in reality we might be sunny and dry for the afternoon. Thursday/Friday/Saturday: large scale broad upper trough will be settling in across the eastern half of the US. For sensible weather in our region, it looks like an extended period of slightly below normal temperatures but relatively dry/comfy weather. Have a very small chance for a brief light shower across the higher terrain of northern VT and northern NY for Thursday, but otherwise chances for rain are less than 10% Friday and Saturday. Highs will range from the upper 60s in higher elevations to lower 70s in the valleys. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Through 12Z Sunday...VFR visibility and vfr sct-bkn sky cover through late evening with plentiful low level moisture. Ceilings lowering to IFR in the Adirondacks/KSLK and MVFR in Green Mountains/KMPV 06-13z timeframe with passage of upper trough. After 12-13z vfr scattered clouds. Surface winds southwest to west. Outlook... Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX. Monday Night: VFR. Slight Chance SHRA. Tuesday: VFR. Chance SHRA...Slight Chance TSRA. Tuesday Night: VFR/MVFR. Likely SHRA. Wednesday: VFR. Chance SHRA. Wednesday Night: VFR. Slight Chance SHRA. Thursday: VFR. Slight Chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Hanson NEAR TERM...Hanson SHORT TERM...Hanson LONG TERM...Nash AVIATION...Hanson

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