Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 241951 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 351 PM EDT Mon Sep 24 2018 .SYNOPSIS... Another quiet night is expected across the North Country before a warm front moves through the region on Tuesday. Strong and gusty southerly winds will accompany period of moderate to heavy rainfall Tuesday morning and Tuesday afternoon. Winds will diminish Tuesday night but pick back up again on Wednesday ahead of a cold front that will push through the region during the afternoon and evening hours. Some strong thunderstorms are possible with the cold front with a slight chance of a severe thunderstorm or two. Following the cold front, quieter and drier weather is expected through Saturday before the next system approaches from the west. && .NEAR TERM /THROUGH TUESDAY NIGHT/... As of 301 PM EDT Monday...The quiet before the storm is being observed across the North Country this afternoon with most places seeing a beautiful fall day. Satellite data continues to show a pocket of stratus entrenched across eastern Vermont as a marine air mass has banked up along the Green Mountains. Froude numbers are nearly zero this afternoon which suggests that flow is subcritical and blocked. A stable air mass caps the atmosphere above this stratus deck which has made it very difficult to mix out the cloud deck but latest imagery is showing clouds eroding from the east. This trend will continue into the overnight hours which will help break up the clouds but several places over eastern Vermont may miss out on sunlight this afternoon. Heading into tonight, clear skies will be seen through midnight before cloud cover begins to increase from the southwest. An approaching warm front will also allow for rain chances to increase after midnight although steady rainfall isn`t expected until the early morning hours on Tuesday. By 8 AM Tuesday, rain will have already tracked across northern New York and made it into central Vermont. Like the event a few days ago, it looks like a large portion of the area will see around a half of an inch of rainfall as the warm front lifts through the region. There are a few signs of potential upslope/downslope components as Froude numbers remain below 0.5 through the frontal passage but frontogenesis in the low and mid levels may be enough to overcome this blocked flow. Should the blocked flow develop, higher rainfall amounts will be possible on the western slopes of the Adirondack Mountains. The current forecast reflects a solution where the upper level support in the low to mid levels will be enough to overcome the strengthening southwesterly LLJ with pretty uniform rainfall amounts seen across the North Country. While the warm front approaches the region, high pressure situated over New England will shift eastward over the Atlantic Ocean. As this happens, the pressure gradient over the North Country will compact and gusty winds will begin to develop toward sunrise on Tuesday. Southerly winds in the 10 to 20 mph with gusts to 35 look pretty common through the afternoon on Tuesday before the boundary layer decouples and lighter winds will be observed. Tuesday night will end up being a pretty warm and muggy night as temperatures warm through the night as both 925 mb and 850 mb quickly warm behind the warm frontal passage earlier in the day. The highs on Tuesday will likely end up being the low for Wednesday with temperatures warming overnight. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... As of 334 PM EDT Monday...Active weather day expected Wednesday, with possible tstms with gusty and locally damaging winds possible. Will see moderately strong S-SW gradient flow in place during the day Wednesday, in advance of strong cold front approaching from sern Ontario. Anticipate south winds 15-25 mph - with gusts up to 35 mph - especially with channeled flow in the Champlain Valley. Anticipate mostly cloudy conditions, but dewpoints will climb into the mid- 60s with continued south winds and moisture advection in advance of the cold front. Deep-layer wind fields also become moderately strong in advance of the bndry, with sfc- 6km bulk shear values of 45-55kt. As is typical with a fall system, some question as to overall convective instability, as lapse rates will be nearly moist adiabatic and insolation should be limited. That said, rich PBL moisture may contribute to narrow axis of SBCAPE 500-1000 J/kg that could drive tstm potential with strong large-scale forcing along the frontal bndry. Anticipate a narrow band of showers, with potential for embedded tstms. If storms can become linearly organized, could see a damaging wind threat during the late aftn/evening hours across nrn NY and thru the wrn half of VT. In agreement with SPC slight risk on day 3 for potential wind damage threat. Will continue to monitor this potential. Otherwise, will see band of moderate rainfall along the cold front along with a westerly wind shift and low-level CAA heading thru Wednesday night. Looking for daytime highs on Wednesday in the 74-78F range, followed by lows Wednesday night mainly in the 40s, except locally in the lower 50s near Lake Champlain and across the upper CT river valley. Additional rainfall amts Wednesday generally 0.3-0.6", but may be locally higher with any convective storms. Thursday will feature much quieter wx as ridge of high pressure builds into the nern CONUS, with light wind conditions. Increasing sunshine thru the day with highs mainly in the low- mid 60s. Should see dewpoints back down into the low 40s in post-frontal air mass. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 334 PM EDT Monday...No significant weather expected through the long-term forecast period. Best rain chances (40-50% PoPs) during the extended to Saturday night into Sunday as cold front moves from west to east across the North Country in progressive mid-upper level flow pattern. Otherwise, conditions appear mainly dry with seasonable temperatures for late September. Generally looking for highs in the 60s, with lows mainly in the 40s. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... Through 18Z Tuesday...Marine stratus has left TAF sites in eastern and southern VT with MVFR ceilings ranging from 1800 to 2200 ft. It doesn`t look like this cloud deck will be dissipating any time soon. In fact, it may not be until sunset that the ceilings finally begin to climb back to VFR. Elsewhere, VFR conditions have persisted with gradient winds beginning to increase as high pressure begins to slide east of the area. For tonight, cloud cover will begin to increase from the southwest as a warm front moves toward the region. As cloud cover increases overnight, so should rain chances. By 10Z Tuesday, rain will begin to move into northern New York and the leading edge will move into eastern Vermont by 14Z. Periods of moderate and even heavy rainfall is expected with this rainfall which will lead to MVFR and occasionally IFR visibilities in heavier rainfall. In addition on Tuesday, gradient winds will really ramp up. After 12Z, it looks like most places will see winds from the south around 15G25kt with some stronger winds possible at KBTV. Outlook... Tuesday Night: Mainly MVFR, with areas IFR possible. Likely RA. Wednesday: Mainly MVFR, with local IFR possible. Likely SHRA, Chance TSRA. Wednesday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Thursday: VFR. NO SIG WX. Thursday Night: VFR. Slight chance SHRA. Friday: VFR. Chance SHRA. Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Clay NEAR TERM...Clay SHORT TERM...Banacos LONG TERM...Banacos AVIATION...Clay

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