Area Forecast Discussion
Issued by NWS Burlington, VT
Issued by NWS Burlington, VT
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225 FXUS61 KBTV 052328 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 728 PM EDT Fri Jul 5 2024 .SYNOPSIS... Isolated showers and storms will continue tonight, and then become more widespread Saturday morning. After brief drying, some more showers and storms are likely to develop Saturday afternoon, especially over Vermont. Drier days are forecast for Sunday and Monday although remaining humid at the ground and warm. Another round of showers and thunderstorms likely late Tuesday into Wednesday along a cold front passage. Slightly cooler and less humid air returns midweek. && .NEAR TERM /THROUGH SATURDAY NIGHT/... As of 724 PM EDT Friday...Main adjustment was to alter precipitation chances mainly across north-central Vermont and the Adirondacks, lowering to match observed trends from satellite imagery. Low level instability rapidly waned with dry air mixing down while a mid layer cloud deck moved over these areas. This resulted in a rapid diminishing in cumulus development. As such, these areas will likely remain stable until elevated instability moves over around midnight. Elsewhere, a few showers are ongoing, but nothing too remarkable. Localized moderate to heavy showers are possible given the lack of steering flow. Previous Discussion...BTV has managed to hit 90 for a second day in a row now. A subtle upper trough and plenty of warm, moist air is supporting some isolated convection across the region. Some dry mid- level air impinging across the area is helping to limit extent, and lack of deep layer shear is keeping everything garden variety without much entrainment of that mid- level dry air. There won`t be much change to the forecast tonight. There may be some fog due to lowering surface pressures, light wind with high moisture, and some rainfall. The primary fog areas will be the favored valleys and wherever rain falls today. Lows ranging lower 60s in the Dacks and Northeast Kingdom, and mid 60s to lower 70s across the rest of the forecast area. For tomorrow, rounds of showers and storms will be the theme. A surface trough presently over Kentucky will lift northeast. With accelerating southwesterly flow and even richer moisture, showers and thunderstorms could occur even overnight. Then, a vigorous vort max rounds a negatively tilted upper trough. Alongside the activity from Kentucky, this appears to start secondary development of low pressure. High resolution guidance is now depicting a healthy swath of rain lifting into the region between 6 AM and Noon. Some rain could be locally heavy as this is tied to the warm front with 1.75 to 2 inch PWATs. This will lift northeast, and then some relatively drier air will filter in the region. The broader extent of rain will likely suppress heating. So high temperatures have been lowered for tomorrow, and are now mainly in the low to mid 80s, though some upper 80s may still take place in the Connecticut River Valley. With the high humidity still in place, there may still be some heat indices in the lower 90s there tomorrow. Showers and thunderstorms will fire later in the day, but mid- level lapse rates will be poor, and there appears to be dry mid- level air behind the morning activity. This may hamper updrafts combined with the cooler surface temperatures now expected. With shear in the 55-60 knot range at 0-6km, it appears likely to destructively interfere with storms. Still, additional heavy rain may take place in shower activity. Combined with the morning activity about 0.33 to 0.75" is broadly expected, but a swath up 1.50" is likely. The highest chance will be across Bennington and Windham County where the HREF probabilities of exceeding 1.50" in 24 hours to be about 30-50 percent, while it is generally less than 30 percent in Rutland and Windsor County. Given flash flood guidance in southern Vermont is relatively high due to being somewhat dry as of late, it is possible that the area can manage the rain. But we`ll keep an eye. Conditions remain humid, and so temperatures will generally stay in the 60s Saturday night with some isolated showers in the upper trough still. && .SHORT TERM /SUNDAY THROUGH MONDAY/... As of 319 PM EDT Friday...As mid-level trough and strong mid-upper jet depart to the northeast of the region on Sunday, expecting gradual 700-500mb height rises with Sunday being the drier of the two weekend days. Indicated just a 20 percent chance of an early morning shower in n-central/nern VT with departing mid-level trough axis, followed by mostly sunny and warm conditions areawide. Valley highs will generally reach the 83-88F range. Little overall change in dewpoints, with very humid conditions continuing (dewpoints in the upper 60s). Weak high pressure builds in Sunday night with a humid night expected. Should see some patchy fog overnight with lows only dipping into the mid-60s, except near 60F for the northern Adirondacks and far nern VT. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... As of 319 PM EDT Friday...Broad mid-upper level trough and cyclonic flow returns to the Great Lakes and Ohio Valley for the mid-week period next week, with a continued very warm, humid air mass with S-SW low-level flow across NY and New England. Appears that precipitable water values will remain above climo averages, with PW values of 1.50-1.75" likely for Tuesday and Wednesday. This should be our most favorable period of mid-level/large-scale forcing as a shortwave trough progresses through the region from W-E per 12Z GFS and ECMWF deterministic forecasts. Have indicated 60-70% PoPs late Tuesday into early Wednesday areawide, with a chance for embedded thunderstorms given low-moderate CAPE values. Mid-level lapse rates aren`t very impressive at this early stage in the forecast, but sfc temperatures near 90F and hot PBL conditions may be sufficient to support a few stronger thunderstorms late Tuesday into Tuesday evening, and we`ll need to continue to monitor that potential in the coming days. Any thunderstorms would also have the potential to bring brief heavy rainfall. Should see a slight cooling trend Wed/Thu with highs in the low-mid 80s. Current trends indicate lesser precipitation chances for the late Wednesday through Friday time frame. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Through 00Z Sunday...Showers are few and far between across the forecast area this evening, so VFR is the main condition for the next few hours. A stationary front is draped across northern NEw York and Vermont, which is resulting in some differing wind directions for different sites. Those north of the front are having north to northeasterly winds, while those south of the front experience southerly winds, all generally under 10 knots. Overnight tonight, winds will become light and variable, allowing for patchy fog to develop as or slightly before rain overspreads from west to east. Highest chances for IFR or LIFR conditions in fog and low clouds will be at EFK, MPV, and RUT, from 09Z-16Z Saturday, though other sites may also be impacted during this period as well, especially as moderate to heavy rain becomes another factor in potential IFR/LIFR conditions. Embedded thunder is possible but not likely with this batch of rain showers. Conditions should begin to improve around 18Z-21Z Saturday as rain shifts eastward and winds increase again out of the southwest. Outlook... Saturday Night: VFR. Chance SHRA. Sunday: Mainly VFR, with local MVFR possible. NO SIG WX. Sunday Night: VFR. Patchy BR. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. Chance SHRA, Chance TSRA. Tuesday Night: MVFR/IFR conditions possible. Likely SHRA. Wednesday: MVFR/IFR conditions possible. Likely SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Haynes NEAR TERM...Boyd/Haynes SHORT TERM...Banacos LONG TERM...Banacos AVIATION...Storm