Area Forecast Discussion
Issued by NWS Burlington, VT

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603 FXUS61 KBTV 250809 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 409 AM 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 /THROUGH TONIGHT/... As of 409 AM EDT Monday...Potential for strong to possibly severe storms will exist across the area this afternoon and evening. Today...convective debris clouds and or some convection is expected 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. && .SHORT TERM /TUESDAY 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 SUNDAY/... As of 409 AM EDT Monday...00z guidance suite in okay agreement Thursday and Friday, but then start to diverge rapidly for the weekend and even more so early next week. The 00z GFS has made the biggest changes from earlier runs, while the ECMWF has been more consistent, so perhaps that is a signal that the GFS solution is not as robust? At this point, not too sure, so as typical, kept with a model blend for the forecast. Some specifics: Thursday/Friday: Looks like some height falls across the northeast US as an upper trough settles in across eastern Canada. Models also show moisture pooling into the region from the west and southwest. So can`t rule out a few showers. Doesn`t look like a lot of instability, so t-storms might be limited (but don`t hold me to that). With the slight lowering of heights, temperatures aloft will also cool down a bit. Looking more like 925mb temperatures of 18-20C Thursday which would support low-mid 80s for highs and then even a bit cooler Friday. Went with the model blend for PoPs, so I`ve got a good amount of 20-30% chance of showers both days. Could be that one of those days ends up totally dry, but too much variability in the models to have high enough confidence in that. Saturday/Sunday: As we go into the weekend, the ECMWF swings a shortwave through on Saturday night and then parks it just to our northeast, keeping us in slight troughiness into early next week. At face value that would mean showers/t-storms over the weekend and then slightly cooler than normal temperatures. The GFS on the other hand, departs from previous runs, and does not have that shortwave any more. In fact by early next week it is building the heat wave ridge north and east across the Great Lakes and into the northeast. Not sure if I buy that right now. So the forecast features a blend that turns out to be pretty much a climatological normal forecast. Highs in the 70s to lower 80s with a chance of showers. Don`t cancel outdoor plans at this point, as that weekend forecast is bound to change between now and then as we gain clarity. && .AVIATION /08Z Monday THROUGH Friday/... Through 06z 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 brief periods of MVFR/IFR conditions along with gusty winds and moderate to severe turbulence. At this time the locations likely to see these lower flight categories are KSLK...KPBG...KBTV...KMPV...and KRUT. Light winds this morning becoming south and southwest this afternoon at speeds in the 5 to 15 knot range. Outlook 06z Tuesday through Friday... 06z Tue - 00z Fri: Mainly VFR under high pressure. Isolated showers possible Wed/Thu afternoons. 00z Fri - 00z Sat: Increasing chances for widespread MVFR showers and isolated thunderstorms. && .MARINE... The threat for thunderstorms will exist this afternoon into early evening across Lake Champlain. Storms will move west to east across the lake and as has been the case with the last three weather events...any storms will have the potential to produce gusty winds...small hail...heavy downpours...and frequent lightning. Boaters should keep an eye on the sky this afternoon and evening and have a plan in place to seek safe harbor at the first sign of threatening weather. Stay tuned to our latest forecasts and any lake thunderstorm advisory that gets issued. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Evenson NEAR TERM...Evenson SHORT TERM...Nash LONG TERM...Nash AVIATION...Evenson/Lahiff MARINE...Evenson

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