Area Forecast Discussion
Issued by NWS Burlington, VT

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998 FXUS61 KBTV 251610 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1210 PM EDT Fri May 25 2018 .SYNOPSIS... Summerlike weather arrives today as high pressure brings warm temperatures to the area. A cold front will approach from the north tonight, and linger across the region over the weekend. As a result, expect an increase in cloud cover, cooler temperatures and chance of showers and thunderstorms through the period. A few of the storms could produce locally heavy downpours. && .NEAR TERM /THROUGH SATURDAY/... As of 1210 PM EDT Friday...Overall forecast in good shape. Areal coverage of mid level clouds is increasing over the area as of midday and will affect temperatures for the rest of this afternoon. Expect steady or slowly falling temperatures over Vermont and a slight increase over northern New York later today with a break in the clouds. Have had some reports of sprinkles and have expanded the slight chances threat to most of the area this afternoon. Rest of forecast remains unchanged. Previous Discussion... Warm temperatures remain in the cards for today as a westerly surge of continental air has arrived overnight on the nose of robust 50+ kt mid-level jet (Whiteface Summit winds of 50G59kt as of 330 am). High temperatures should top out in the upper 70s to lower 80s area wide with perhaps a few mid- 80s in favored downslope areas of the Champlain and CT River Valleys. There will also be a broad increase in columnar moisture by this afternoon with model- averaged PWAT values increasing to near 1.5 inches by early evening. On the nose of this higher moisture variable mid- level cloud cover should advect across central and northern counties through the day and especially by early evening. Only limited dynamical support for lift exists however, so outside a very brief light shower or sprinkle in these northern areas mainly dry weather is expected through late afternoon. With the boundary layer deepening into the 850-825 mb level this afternoon gusty winds also look like a certainty with west to southwesterly peak gusts topping out in the 20-30 mph range in the noon to 500 pm time frame. By this evening a more concerted push of moisture and lower end mid level instability advect into the region in advance of a backdoor cold front dropping south/southwestward from southern Quebec. I`ve largely ignored the swaths of excessive QPF offered by some of the 00Z hi-res NAM/WRF output given only marginal lifting mechanisms, though weak bundles of shortwave energy traversing the area in the west to northwesterly flow aloft should be sufficient to produce scattered showers across the northern tier of counties accordingly. An isolated storm also can`t be ruled out but coverage of storms should be on the low side. Mainly dry weather continues across southern counties. Low temperatures a bias-corrected consensus blend of guidance with values generally ranging from the mid 50s to lower 60s in milder valley locales. The start of an active weekend of weather then begins on Saturday as a fairly sharp backdoor cold front is forced south/southwest into the area by expansive high pressure bridging east across central Quebec. Moisture pooling to the south of the boundary along with CAPE values from 250-750 J/Kg should be sufficient to generate numerous showers and a band of embedded thunderstorms by afternoon. Some variability exists within this morning`s models on the exact zone of convective development, though a consensus solution would suggest areas from the Adirondacks east through central and southern VT have the highest probabilities where brief heavier downpours will be possible. The thunder threat across the northern tier isn`t non- zero either, but our current forecast of a morning frontal passage suggests an earlier arrival of a cooler, more stable airmass under increasingly cloudy skies. Maximum temperatures will also support this timing with another day of upper 70s/lower 80s across the south, and upper 60s to lower 70s across the northern tier. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 347 AM EDT Friday...In the evening hours the backdoor cold front will continue to sag slowly south across the North Country on Saturday. The front sort of washes out as the flow across Vermont and the western Champlain valley turns west to southwest as a modified marine airmass moves in from the south and east. 925mb temps cool in this region with increasing humidity, however across the Saint Lawrence southerly flow continues and a much warmer airmass will hold in place. That will lead to lows Saturday night east of the Adirondacks in the low to mid 50s with near 60 for low temps in the Saint Lawrence Valley. The modified marine air mass will lead to stabilization of the boundary layer heading into Sunday under mostly cloudy skies. With the stable boundary layer we should be mostly precip free across the Champlain Valley and the rest of Vermont. Its a different story across the Saint Lawrence valley where we`ll see partly cloudy skies with a rapidly destabilizing atmosphere. Temps should warm into the low 80s with dew points in the upper 50s to low 60s. MUCAPE in the Saint Lawrence Valley increases into the 1000-1500 J/kg by mid afternoon. An upper level trough will swing a shortwave through the Saint Lawrence and that shortwave will be the needed forcing for storms to develop. Combine the shortwave with a PWAT surge and these ingredients will lead to the potential for thunderstorm development with possibly heavy rainfall in the afternoon. CAM models continue to depict bullseyes of 1-2"/hr rates in the region and so we`ll need to monitor any storms closely. The upper level through finally swings through the North Country on Monday and will lead to some additional scattered shower activity on Monday with dry weather returning behind a frontal system Monday night. && .LONG TERM /TUESDAY THROUGH THURSDAY/... As of 347 AM EDT Friday...A ridge of high pressure builds in behind the system on Monday and leads to moderating temperatures. Tuesday should be a pleasant day with semi breezy conditions and temps warming into the mid 70s. We`ll see decent radiational cooling at night with a dry air mass in place and lows will cool into the mid 40s to low 50s. The high will be cresting over the region on Wednesday and it should be another beautiful day across the North Country with above normal highs and slightly above normal lows. The high begins to break down on Thursday and with another round potential showers and thunderstorms Thursday afternoon into Friday. && .AVIATION /16Z FRIDAY THROUGH TUESDAY/... Through 12Z Saturday...VFR thru the period. Winds south to southwesterly from 10-15 kts and gusts from 18-28 kts expected at all terminals through 00Z before abating overnight. Some minor crosswind concerns possible at KBTV/KPBG. SCT/BKN mid level cigs in the 070-120 AGL range to push east across the area in the 12-18Z time frame, before thinning this afternoon. No precipitation other than an isolated very light shower or sprinkle is expected with these clouds. After 00Z SCT/BKN cigs in the 050-080 AGL range push back into the area with an increasing threat of showers from 02-06Z onward, especially at northern NY terminals and KBTV. Outlook... Saturday: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA. Saturday Night: Mainly VFR, with areas MVFR possible. Chance SHRA, Slight chance TSRA. Sunday: Mainly VFR, with local MVFR possible. Slight chance SHRA, Slight chance TSRA. Sunday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Memorial Day: Mainly MVFR, with areas VFR possible. Chance SHRA, Slight chance TSRA. Monday Night: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA. Tuesday: Mainly VFR, with local MVFR possible. Slight chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...JMG NEAR TERM...Evenson/JMG SHORT TERM...Deal LONG TERM...Deal AVIATION...JMG is the U.S. government's official web portal to all federal, state and local government web resources and services.