Area Forecast Discussion
Issued by NWS Burlington, VT

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095 FXUS61 KBTV 251936 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 336 PM EDT Mon Jul 25 2016 .SYNOPSIS... Above normal temperatures are expected today along with increasing chances for showers and thunderstorms this afternoon and evening. Some of the storms may contain gusty winds...small hail...and heavy downpours. Quieter weather is expected on Tuesday and Wednesday with maybe a few showers up near the Canadian Border both days. The above normal temperatures will continue through midweek as well. && .NEAR TERM /UNTIL 11 PM THIS EVENING/...
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As of 336 PM EDT Monday...Have lowered the chance for showers and thunderstorms for today until after 21z when we may get into the clearing and get some convection started. Potential for showers and thunderstorms still exists for this afternoon and evening, with strong storms possible in the St Lawrence Valley and portions of Central and Southern Vermont. Previous discussion follows. Today...going forecast in good shape with increasing clouds and weakening convection moving into the Saint Lawrence River Valley. Convective debris clouds and or some convection will continue to move across the North Country this morning. Moisture advection will be taking place and this will be needed to raise dew points into the 60 to 65 degree range. Warmer 925 millibar temperatures also moving into the region will combine with clearing skies to raise temperatures into the 80s to around 90. This should create CAPE values in the 750-1500 J/kg range with the lower of this range in the Northeast Kingdom of Vermont and the higher values of the range over south central Vermont and the far southern portions of the northern Adirondacks. Where this greater instability will develop there will also be increasing flow aloft and this deep layer shear should allow for storms to become organized and reach strong to severe levels. Essentially this will be south of a line from Ogdensburg to Middlebury to White River Junction. North of that line the potential for strong storms will exist. Thus will maintain enhanced wording in the forecast of gusty winds and small hail and include heavy downpours as higher precipitable water values develop. Potential for these stronger storms will exist between 18z and 03z. The increasing deep layer shear this afternoon is the result of an approaching shortwave trough moving into the eastern Great Lakes late in the day. Dynamic support will be increasing with the trough and upper diffluence in advance of the trough suggests synoptic scale lift will be sufficient to have the showers and storms be fairly widespread in nature. Thus like the idea of likely precipitation chances just about everywhere this afternoon and into the first half of the night. Tonight...as mentioned above any potential threat for stronger storms will exist until about midnight but precipitation will be ending from west to east as the evening wears on. No precipitation is expected after midnight. Clouds and low level moisture will linger tonight and this will help to keep low temperatures in the 60s.
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&& .SHORT TERM /11 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... As of 409 AM EDT Monday...Fairly tranquil mid-summer weather expected for the period. On Tuesday we`ll see some daytime heating cumulus develop across the region (a little more so over the higher terrain). Can`t rule out a lingering sprinkle/light shower across the higher terrain of northeast Vermont due to slightly deeper moisture and the relative nearness of the upper trough. We`ll still be an overall west/northwest flow aloft, so the airmass will continue to be warm as we remain on the far fringes of the massive heat across the center of the country. 925mb temperatures Tuesday will generally be in the range of 18C (north) to 21C (south). This would support high temperatures in the 80s everywhere, and perhaps pushing 90F in some of the southern valleys. Decent amount of boundary layer mixing, so by afternoon we should tap into some slightly stronger winds up at 4000-5000ft. We should see some gusts in the 20-25mph range in spots. Clear and calm Tuesday night. High pressure at the surface and weak ridging aloft will ensure a clear night. Looks like we`ll have patchy fog develop in those typical areas across the `Dacks and Eastern Vermont as overnight lows are expected to drop below the crossover temperature (dewpoint value midday Tuesday). Lows across the region will range from the 50s to lower 60s. Wednesday should be a very warm to hot summer day. With the continued westerly flow aloft, a little bit more of that heat off to our west will advect in. Guidance is pretty solid in showing 925mb temperatures of 23-24C. This suggests high temperatures in lower elevations will top out in the upper 80s to lower 90s. For whatever reason, the suite of guidance we can look at had a number of members that only indicated mid-80s for highs, so I ignored all but the warmest guidance. There will be a weak front lurking north of the US/Canada border that should spark a few t-storms up there. We`ll stay dry for the day. That front may ooze a bit south during the evening, so a rogue t-storm along the border is a possibility Wednesday night. Have kept PoPs only in the 15-25% range however. Should be a relatively warm night with most of us seeing temperatures only bottoming out in the 60s. A little muggy as well. && .LONG TERM /THURSDAY THROUGH MONDAY/...
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As of 336 PM EDT Monday...Surface ridge building in from south central Canada with light north-northwest flow will coincide with 500mb troughing providing a low chance for showers on Thursday. Continued ridging at the surface and slight ridging aloft will keep Friday dry before low pressure system develops to the south/west and brings a chance for precipitation late Friday. Model guidance diverges on evolution of this system associated with two areas of vorticity embedded in the 500mb flow. 12Z ECMWF develops these features into a double barrel surface low pressure system late in the week into the weekend. While 12Z GFS keeps mid level vorts along more southerly route and surface high pressure over southwestern Quebec and the northern New England. High uncertainty in the pattern beyond early Friday. Both models show mid level troughing across the Northeast late Saturday with the GFS much broader than the ECMWF. With these differences noted, have stuck with Superblend with chances for precipitation through Monday. Temperatures generally expected to be near normal, but highly dependent on variability of cloud cover and precipitation.
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&& .AVIATION /20Z Monday THROUGH Saturday/... Through 18z Tuesday...VFR conditions will exist through much of the period. However...between 18z and 03z we are expecting scattered showers and thunderstorms to move east across the area resulting in periods of MVFR/IFR conditions along with the potential for gusty winds...small hail...heavy downpours...frequent lightning... and moderate to severe turbulence. At this time the locations likely to see these lower flight categories are SLK...PBG...BTV...MPV... and RUT. Light winds becoming south and southwest this afternoon at speeds in the 5 to 15 knot range. Outlook 18z Tuesday through Friday... 18z Tue - 00z Fri: Mainly VFR under high pressure. Isolated showers possible Wed/Thu afternoons. 00z Fri - Sat: Increasing chances for widespread MVFR showers and isolated thunderstorms. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Evenson/Neiles NEAR TERM...Evenson/Neiles SHORT TERM...Nash LONG TERM...KGM AVIATION...Evenson/Lahiff/Neiles

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