247 FXUS61 KBTV 250508 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 108 AM EDT Wed Aug 25 2021 .SYNOPSIS... Afternoon high temperatures in the mid 80s to near 90 degrees are expected through Thursday before a cold front moves through the region and brings a welcome reprieve of more seasonal temperatures. Scattered showers and thunderstorms will be possible Thursday and Thursday night but otherwise we are looking dry through the remainder of the week. && .NEAR TERM /THROUGH THURSDAY/... As of 104 AM EDT Wednesday...No major changes to the forecast this morning other than to increase high clouds across northern New York. An MCS across the Mid-West has blown some cirrus over the northern New York and will overspread Vermont over the next several hours. This will likely dampen the fog potential over the region but we should still see some isolated patchy dense fog through the overnight hours. Otherwise, the forecast remains well on track. Previous discussion...Relatively quiet near term period with only concern being the heat and humidity. We managed to reach 90 degrees here at BTV this afternoon, however afternoon dewpoints have been able to mix out in some places to more "comfortable" levels in the mid 60s. This has helped keep heat indices in the upper 80s to right around 90 area wide. High pressure continues to work into the area tonight with light winds and clear skies expected. Areas of valley fog are likely, especially in the favored river valleys where pockets of dense fog are possible given ideal radiational conditions. Little change expected to the forecast for tomorrow with temperatures a couple degrees warmer than today (upper 80s to right around 90 for much of the area). However as noted previously, the airmass in place is relatively dry therefore expected moisture to mix out in the afternoon much like today which should help mitigate oppressive heat concerns. Regardless, temperatures will still be hot and heat indices will be in the low 90s, however we'll remain just shy of heat advisory criteria. Wednesday night flow will begin to back out of the SW. Chances for scattered showers are possible late Wednesday night associated with decaying convecting out of the upper mid-west. Overnight lows will remain above normal in the mid 60s to low 70s. && .SHORT TERM /THURSDAY NIGHT/... As of 402 PM EDT Tuesday...One last day of hot weather is on tap for Thursday after morning decaying showers and associated clouds dissipate. Similar to Wednesday, peak heat index values will be mainly in the 90 to 95 range, with superadiabatic low level lapse rates promoting good mixing. Thursday continues to have the greatest potential for thunderstorms this week; however, chances are low in any one location. Both a delayed surface cold frontal passage and lack of dynamic forcing or height falls aloft moving through the area point to isolated thunderstorms at best during the day. Forecast soundings indicate a stable layer near 700 millibars, with winds backing to the northwest above that pressure level which will support drying air. Eventually, with surface based CAPE soaring into the 1500 to 2500 J/kg range, clouds will start bubbling up. Any cells that can form will potentially become strong given the favorable mid level lapse rates exceeding 7 degrees C per km, but effective wind shear will likely be limited to around 20 knots minimizing the severe threat. Increasing coverage of showers and thunderstorms is expected ahead of the cold front Thursday evening into the night with some indication that better chances will be near the International Border. Without large height falls ahead of the front, widespread thunderstorms appear unlikely during this period, as well. Any storms should produce briefly heavy rainfall as warm cloud depths rapidly increase to near 12,000 feet just ahead of the front. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 402 PM EDT Tuesday...Quiet weather and near to slightly below normal temperatures - highs ranging through the 70s and lows mainly in the 50s - are on tap for Friday and Friday night as high pressure exerts control behind the cold front. Have a slight chance of showers in most areas during the afternoon, owing to some lingering instability and expectation that convective temperatures will be reached given ample sunshine during the first part of the day. It still looks like a warm front will quickly spread clouds and rain into the North Country this weekend. The timing of this rain looks a little faster given the model consensus, gradually spreading eastward as soon as Saturday morning with greater chances as the afternoon and evening wears on, especially over northern New York. Southerly flow will be seasonably strong as a pressure gradient between the departing high and low pressure over the middle of the US increases, supporting winds on Lake Champlain in excess of 20 MPH during much of the day. The southerly flow will continue through early next week with additional periods of showers as upper level energy rides northeastward and eastward out of the central US. Low pressure well north of the Great Lakes is forecast to occlude with a strong cold front eventually swinging through the North Country by Tuesday. In advance of the front, if there are enough breaks in the clouds, will see chances of thunderstorms on Monday with otherwise plentiful cloud cover putting a pin in the heat potential. && .AVIATION /05Z WEDNESDAY THROUGH SUNDAY/... Through 06Z Thursday...We are looking at VFR conditions and light winds persisting through the forecast period. The only exception will be pockets of IFR to LIFR fog developing across KSLK and KMPV from 7Z to 13Z this morning. Outlook... Thursday: VFR. Chance SHRA, Chance TSRA. Thursday Night: VFR. Slight chance SHRA, Slight chance TSRA. Friday: VFR. Slight chance SHRA. Friday Night: VFR. Slight chance SHRA. Saturday: VFR. Chance SHRA. Saturday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Sunday: MVFR. Chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...LaRocca NEAR TERM...Clay/LaRocca SHORT TERM...Kutikoff LONG TERM...Kutikoff AVIATION...Clay