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Area Forecast Discussion
Issued by NWS Burlington, VT
Issued by NWS Burlington, VT
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454 FXUS61 KBTV 150604 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 204 AM EDT Thu Aug 15 2024 .SYNOPSIS... Typical summer conditions are lining up for the next few days with generally dry mornings followed by chances for afternoon showers and thunderstorms. Most storms will remain below severe thresholds, though some gusty winds and small hail is possible. Temperatures will be a little above normal with a gradual warming trend going into Friday. Conditions turn slightly cooler and unsettled this weekend, with multiple chances for showers and temperatures near seasonable normal values. && .NEAR TERM /THROUGH FRIDAY/... As of 204 AM EDT Thursday...Isolated thunderstorms continue early this morning, which are now clustered in southwestern St. Lawrence County with the western Vermont/Champlain Valley activity greatly diminished. The northern New York activity was where PoPs were quite low, so aside from capturing radar trends in updated forecast, no substantial changes were made at this time. Still expect patchy dense fog to develop in the river valleys, but with a little more low level westerly wind, its extent and duration look a bit more limited than recent nights. Previous Discussion...Longwave pattern remains relatively consistent over the next 24-48 hours. To our west, an anomalously strong ridge extends from the Mississippi River Valley north and eastward into central/northern Quebec. Further south and east, an upper level low will continue to meander over the Canadian Maritimes, with our forecast area remaining in northerly flow between the two features. While the overall setup features a drier northerly flow, there are several chances for showers/thunderstorms to develop in associated with shortwaves rotating around the western periphery of the upper low. Diurnal showers with some embedded thunderstorms are expected this afternoon into overnight tonight in association with several of these shortwaves. Deep moisture will initially be limited this afternoon, with water vapor satellite showing a dry layer pressing southward through our CWA. Observed dewpoints are in the 50s for much of the area, with a few localized readings into the 60s. However, better moisture can be seen to our north, poised to drop southward into our area this evening into overnight. The nocturnal timing of the shortwaves will keep storms going past sunset with overnight MUCAPE values ranging from 500 to 1000 J/kg. However, will have a surface inversion develop overnight which will tamper any threat for overnight severe, so any nocturnal storms should remain below severe thresholds. Will also see some fog develop in climatologically favoured valleys, though any nocturnal showers/storms would impact fog development. For Thursday, little change in the overall pattern. Expecting another round of afternoon showers and thunderstorms to develop, with slightly greater coverage than today`s due to better depth of available moisture to work with. Updraft helicity ensemble neighborhood probabilities highlighting eastern Vermont as the area of focus for tomorrow, which lines up with the best overlap in our CWA of deeper moisture, decent instability (1000 to 1500 J/Kg SBCAPE), and marginal shear (around 15-20 knots 0-6 km bulk shear). While thunderstorms will be possible throughout our CWA, eastern Vermont looks to have the better chance for severe storms containing some gusty winds and small hail. The marginal shear will generally temper any widespread severe threat, and thus we are included in the SPC General Thunder outline which still looks reasonable. Otherwise, look for another warm day Thursday with highs in the 80s for much of the area. && .SHORT TERM /FRIDAY NIGHT/... As of 306 PM EDT Wednesday...Ridging will briefly cross the region on Friday, so generally expect dry conditions to end out the work week. That being said, it will be warm and humid (highs in the 80s and dewpoints in the low/mid 60s) so can`t rule out a few showers developing over the higher terrain during the heat of the afternoon. Any activity that is able to form will wane during the evening as we lose daytime heating. However, expect shower chances to start increasing from the west Friday night ahead of our next system, approaching from the Great Lakes. Lows will be somewhat uncomfortable as moisture increases late; most spots will remain in the 60s overnight. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 306 PM EDT Wednesday...Unsettled weather is expected through the weekend and into early next week as a slow-moving upper low trundles eastward from the Great Lakes and eventually across our region. While not particularly note-worthy compared to what we`ve experienced at times this summer, it will be fairly humid with PWATs generally 1.50-1.75 inches through much of the period. As noted by the previous forecaster, the question will be how much deep convection we can get. At this point, it does appear that there will be periods that will favor heavier rainfall rates, with deep warm cloud depths and little forward movement/back building. Not overly concerned at this point, but given recent heavy rainfall and wet soil conditions, trends will need to be monitored. Note that our entire forecast area continues to be included in the Marginal Risk in both the Day 4 and Day 5 Enhanced Rainfall Outlooks, which seems reasonable. Overall rain threat looks highest in NY Saturday and Sunday as the upper trough draws near, but then expands into VT Monday/Monday night as the trough moves eastward, with a cold front eventually moving through sometime in the early to mid week. Daytime temperatures aren`t expected to be especially warm during this time frame with highs only in the mid 70s to around 80, but as mentioned above, it will be muggy, and lows will remain in the 60s for most spots until a frontal passage Monday or Tuesday. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... Through 06Z Friday...Conditions will remain VFR through much of the period. The main aviation hazard will be locally dense valley fog in the climatologically favored valleys, although 10 to 20 knots of westerly wind at the top of the nocturnal inversion is present. While these winds are expected to relax somewhat, this scenario will limit duration of fog. Greatest chances of fog are between 09Z and 12Z at MPV, SLK, and EFK. Showers and thunderstorms will develop during the afternoon, with coverage at TAF sites expected to be isolated leading to use of VCSH at this time. Greatest chances are between 18Z and 22Z. Winds will be mainly calm at the surface through the overnight, then becoming northwesterly at most sites between 15Z and 18Z at 4 to 8 knots, and diminishing again towards 00Z. Outlook... Friday: VFR. NO SIG WX. Friday Night: VFR. Chance SHRA. Saturday: VFR. Chance SHRA. Saturday Night: VFR. Likely SHRA. Sunday: Mainly MVFR, with areas VFR possible. Likely SHRA, Slight chance TSRA. Sunday Night: Mainly MVFR, with areas IFR possible. Chance SHRA. Monday: Mainly IFR, with local MVFR possible. Likely SHRA, Slight chance TSRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Duell NEAR TERM...Duell/Kutikoff SHORT TERM...Hastings LONG TERM...Hastings AVIATION...Chai/Kutikoff