Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 222235 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 635 PM EDT Fri Jul 22 2016 .SYNOPSIS... Scattered showers and thunderstorms are expected this evening... largely across Northern New York but especially Northern Vermont. More scattered showers and thunderstorms move across the North Country on Saturday and yet another possibility of showers and thunderstorms late Monday. Meanwhile Sunday still looks dry and seasonable. && .NEAR TERM /THROUGH SATURDAY/... As of 628 PM EDT Friday...Finally a few showers/storms have fired up but very weak. The main activity is across Maine and ahead of shortwave just NW of Ottawa where both locations have numerous thunderstorms. There is some convective activity in an extrapolated line between both features just north of international border ad believe this will fire up within the next few hours but given the trend in expectations has been lowered feel isold svr threat only...thus have taken out enhanced wording. Combination of BTV4 and HRRR has highly been used through 06z sat. Previous discussion...A HOT afternoon with temperatures at mid-afternoon in the mid 80s/ low 90s across the region with dewpoints in the 60s. As of 3 pm...BTV has reached 94 degrees. Last occurrence was just 9/7 of last year(2015). Despite SFC based CAPES in the 1500-2500+ J/KG range enough drying at mid-levels and lack of a lifting mechanism has kept things in check. A strong vort across Quebec has fired up some storms headed for far northern Maine thus SVR WATCH has been posted there. As advertised the last day/two our triggers were mainly expected this evening and that still holds. Plenty of Low level instabilty...shortwave trough approaching as well as nose of 300mb and 500mb jets moving into area by 00z Sat enhancing any lift. Also..Northern VT/NY will be on the tail of the Quebec system moving across Maine. Models are in general agreement of tstm activity between 21z Fri-00z Sat largely across the northern areas with eventual shift into nrn VT only. Dry air aloft....decent 30-40kts 0-6km shear still could account for isold/sct damaging winds and large hail. Later tonight...Any shower/thunderstorm activity wanes after midnight but still can`t rule out a few showers across NC-NE Vermont. There will be enough breaks across area that some patchy fog around especially where it rains this evening. lows mainly in the 60s. Saturday: A potent shortwave expecyed to move across our area in the afternoon. The dynamics are expected to kick off thunderstorms (actually, there will likely be a cluster of thunderstorms as well with that shortwave that will move southeast out of Quebec and into our region). Each model has a differing evolution of the convection, and is again a symptom of just how sensitive the models are to this type of weather pattern that is driven by mixed layers, elevated and low level instability and boundary layer details. Taking a blend of the models suggests that we`ll have CAPE values perhaps up to 1000 J/kg which is decent enough to drive convection. NAM has 30-40kts of shear, GFS is less than 30kt. Suppose we can`t totally rule out a stronger storm with gusty winds here or there. Looks like the highest chances for storms will be from mid-day through the evening and more so from the `Dacks and points eastward. SPC has this same region marked with "Marginal Risk" and at this point, that seems like a good assessment. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... 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. && .LONG TERM /MONDAY THROUGH FRIDAY/... 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. && .AVIATION /00Z Saturday THROUGH Wednesday/... Through 00z Sunday...mainly VFR with a round of showers/thunderstorms this evening...largely across northern 1/3 of response to upper level short wave. This will producing mvfr vis in scattered rain showers perhaps some very brief IFR in thunderstorms. 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. Aft 15z Sat...VFR, with scattered brief MVFR/IFR in showers and thunderstorms. Some thunderstorms may contain strong winds and hail. Outlook 00z Sunday through Tuesday... Sat Ngt...VFR but some localized MVFR/IFR due to patchy fog. 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...SLW NEAR TERM...SLW SHORT TERM...JMG LONG TERM...JMG AVIATION...SLW is the U.S. government's official web portal to all federal, state and local government web resources and services.