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Area Forecast Discussion
Issued by NWS Burlington, VT
Issued by NWS Burlington, VT
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238 FXUS61 KBTV 291155 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 755 AM EDT Sat Jun 29 2024 .SYNOPSIS... Rainfall associated with a warm front will overspread the region this morning, with a brief break in rain before several rounds of showers and thunderstorms develop tonight. Ahead of a cold front, isolated to scattered thunderstorms are expected Sunday, especially from the Adirondacks and points east. By Sunday night, drier air will be ushered in, with seasonable and dry weather on tap to start off July. Some chances for showers and thunderstorms return midweek, potentially impacting holiday activities. && .NEAR TERM /THROUGH SUNDAY/... As of 755 AM EDT Saturday...Forecast was updated with some small adjustments to better match surface observations. Showers, as typical, were relatively quick to overspread much of our region early this morning. Although amounts in most places have been only a trace aside from the Adirondack region, this precipitation has helped lower temperatures and raise dew points relative to forecasted values. Also winds have picked up dramatically over Lake Champlain and adjacent valley locations with 30 to 35 MPH gusts so far. Elsewhere, winds have been slow to pick up in most areas. Think in upcoming breaks in precipitation we will see more widespread breezy conditions develop during the day so no changes were made in the wind forecast. Previous Discussion... No big changes to the weekend outlook. There has been a small downward shift in rainfall amounts, slightly reducing the confidence in flash flooding. At the same time, severe weather potential for Sunday has come up a little bit. In the big picture, a storm system more typical in the cold season will be impacting us throughout the period. The parent low pressure area will be tracking far to our northwest, so forcing for rain today will be driven by isentropic lift and embedded upper level shortwaves in fast southwesterly flow. The initial batch of rain will have some brief heavier downpours, but no thunderstorm chances. This will help moisten a very dry air mass that is currently in place. Objective analysis shows strong moisture advection is occurring this morning, with 850 millibar moisture transport directed at northern New York. So as showers overspread our area and moisten the boundary layer, dew points currently only near 50 degrees will climb into the 60s this morning west of the Adirondacks. The humid air will gradually expand eastward as showers work their way through the region, reaching northeastern Vermont last. At the same time, a strong pressure gradient is helping to produce potent low level winds, which are currently around 30 MPH at 925 millibars. A low level jet surge is expected to arrive from the southwest this afternoon with 850 millibar winds exceeding 50 knots by this evening. Precipitable water will surge to near or just above 2", or near climatological maximum values as a surface warm front pushes through our region. Combined with a strong southwesterly jet, moist upslope flow could enhance rainfall rates in portions of the Adirondack region and Green Mountains. This stronger flow will be eventually be coincident with some drying in the mid levels tonight. As such, we do have potential for wet microbursts as tall skinny CAPE profiles develop from the modifying air mass, featuring increasingly warm and moist low level air and cooling/drying aloft. The latest data has trended towards a break in precipitation after midnight, so PoPs decrease into the chance range (mainly 30-50%). That being said, instability will continue to increase so there could be some nocturnal thunderstorms in the wee hours of the night. Tomorrow as a cold front approaches from the west, a pre- frontal trough will trigger scattered showers and thunderstorms. By this point, the heavy rain potential will be somewhat lower as warm cloud depths decrease. The convective environment looks like it will be characterized as high shear, moderate CAPE, especially in the southern Champlain Valley and southern/eastern portions of Vermont. The shear will be west-southwesterly, or partially perpendicular to the cold front. The storm mode, therefore, will tend to be discrete. Taller storms will be capable of frequent lightning and damaging winds. Thunderstorm chances will shift south and east, most likely during the midday hours. A secondary cold front will follow, with potentially more showers but a minimal threat for thunderstorms, late in the day. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 345 AM EDT Saturday...Surface cold front should be moving through the CWA at the start of this period with showers and t-storms although the strongest activity should have likely exited the region by 00z Mon. Upper level shortwave rotates across the area overnight and clears out the humidity and may ring out any leftover isold/sct showers during the overnight. Upper level trof and shortwave will pass east of CWA by mid-late Mon morning with SFC ridge slowly pushing into the area. Northerly flow will bring in cooler, drier, comfortable air with temperatures in the 70s and dewpoints in the 40s-50s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 345 AM EDT Saturday...SFC and Upper level ridge building into the area Monday night for a clear, crisp cool night with temperatures in the 40s-50s across the area. High pressure still in control on Tuesday with moderating temperatures to near or slightly above seasonable levels with highs in the U70s-L80s.Tuesday night will feature upper ridge axis across the NE and dampening with the approach of a northern stream shortwave with the surface high shifting SE for the development of a return SSW flow and temperatures back into the M50s-L/M60s. Northern stream shortwave shifts east across southern Canada which will dampen further the heat ridge across the southern CONUS. A warm front traverses the area Wed with increased heat/humidity but likely decent amount of clouds which may limit instability. However, pre- frontal trof may try to move during or shortly after peak heating so can`t rule out showers and t-storms late Wed-Wed eve but stay tuned as there are some firework celebrations Wed eve. Highs in the 80s. There are still some timing/model discrepancies about cold front passage overnight Wed or Thu or perhaps the front just washes across the area. Attm, I will go with front still across the region in the morning for some clouds and perhaps a sprinkle or shower with front east of the area by afternoon. Seasonable temperatures U70s-L80s. Again, some inconsistency about next upstream shortwave/trof, similar to the first, with GFS more progressive than ECMWF/Canadian so will lean toward a latter solution with threat of showers possible late Friday or Friday night. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Through 12Z Sunday...VFR conditions with light rain showers around this morning will give way to a round of heavier showers which will be capable of brief IFR conditions, especially after 18Z and in northern New York sites. Prevailing visibilities should be MVFR for most if not all sites. Ceilings will begin to lower with heavier rain as well, but generally down to 1500-3500 ft agl. Southerly winds at BTV will be gusting near 25 knots for much of the next several hours before diminishing gradually tonight, while most other sites see few gusts but 10 to 15 knot sustained winds. At 2000 ft agl, increasing south to southwest winds of 45 to 50 knots necessitates LLWS through most of the period. Outlook... Sunday: Mainly VFR, with local MVFR possible. Chance SHRA, Chance TSRA. Sunday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. NO SIG WX. Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. Slight chance SHRA, Slight chance TSRA. && .HYDROLOGY... The threat for localized heavy downpours and isolated flash flooding remains across our region, with greatest risk in the vicinity of the High Peaks of northern New York. The Weather Prediction Center Day 1 Excessive Rainfall Outlook maintains northern NY in a slight risk, or at least 15% chance of rainfall exceeding flash flood guidance within 25 miles of a given point. Current forecasts indicate between 0.50 and 1.50 inches of rainfall is expected with localized amounts of 1.75 to 2.5 inches possible in the heavier thunderstorm activity late Saturday into Sunday. Please continue to monitor the latest forecast for additional details over this upcoming weekend. && .MARINE... Unseasonably strong winds are expected today. South winds will be in the 15 to 25 knot range, with 25 to 30 knot winds at times over the broad lake. Rough waves are expected to develop in response to the strong winds. Wave heights on the broad lake and inland sea are forecast to reach the 3 to 5 feet range later this morning. Winds and waves will decrease slightly by this evening but remain significant overnight tonight. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Kutikoff NEAR TERM...Kutikoff SHORT TERM...SLW LONG TERM...SLW AVIATION...Kutikoff HYDROLOGY...Clay/Kutikoff MARINE...Clay/Kutikoff