117 FXUS61 KBTV 230546 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 146 AM EDT Mon Aug 23 2021 .SYNOPSIS... Outer bands of tropical system Henri will continue to impact southern Vermont overnight. Additional showers with embedded thunderstorms are possible on Monday with localized heavy downpours, which may result in isolated flash flooding. Warm and humid conditions continue for mid week, before a cold front is possible on Thursday into Friday. && .NEAR TERM /THROUGH TUESDAY/... As of 134 AM EDT Monday...Very little in the way of precipitation this evening. There are a few specks on radar towards Rutland County around 25-30 dBZ. We continue to watch the 00Z guidance come in, and observe sharp mid-level dry air over our forecast area. Probabilistic guidance has continued to decrease as the previous forecaster noted, with HREF probabilities of exceeding flash flood guidance about 10% now, and most ensembles depicting a 20-30% chance of rainfall amounts greater than 1 inch over a 24 hour period. Will be looking for whether storms might be able to produce locally heavy rainfall, and will be making decisions over the coming hours. Previous discussion follows. Flood watch continues for Rutland, Windsor, Orange, and Addison Counties from 12z Monday thru 06z Tues. Fcst still remains rather complex associated with a slow moving tropical system and potential heavy rainfall. 12z guidance has trended south with remnants of Henri on Monday and associated heavier qpf axis. We continue to remain on the northern edge of a sharp north to south precip gradient, which makes for a challenging fcst. Its always extremely challenging to pin point exact locations of qpf associated with a slow moving weakening tropical system and convection. This becomes a nowcasting type scenario on Monday. Our updated fcst remains relatively unchanged with regards to focus being mainly south of Interstate 89 with qpf amounts of 1.0 to 2.0 inches and isolated higher amounts possible. Less than 0.50 north of 89 into northern NY. Given the convective nature of expected precip, any potential flooding will likely be isolated/localized in nature acrs our central-southern VT zones on Monday, but threat at time is decreasing given latest fcst. Tonight, expect outer rain bands impacting Rutland/Windsor counties this aftn to weaken as remnants of Henri slowly moves southwest toward eastern NY and rain shield transitions to western side of system. Meanwhile, strong mid/upper lvl ridge and associated dry air prevails acrs our northern/central VT. The combination of waning sfc instability and individual convective elements moving within the banded structure will limit qpf values in the 0.10 to 0.20 range with isolated higher amounts this evening. Still noting 850mb jet of 35 to 40 knots lifting acrs Rutland/Windsor counties btwn 21-03z this evening, which may result in some localized gusts 30 to 40 mph along the western downslopes of Rutland and higher trrn. With some clearing skies from northern New York into northern VT, some areas of patchy fog is possible, given dwpt temps in the mid 60s to near 70F. Lows very similar to previous several nights. By Monday, remnants of Henri becomes a deep vertically stacked system acrs eastern NY and slowly lift into western MA as westerly flow aloft increases. The exact track of this mid/upper lvl low track wl play a critical role on placement of qpf and how much llvl instability can develop to enhance localized rainfall rates. Crnt guidance has been heaviest qpf just south of Rutland/Windsor counties, but a slight 10 to 20 mile jog north, changes the equation. So for consistency and messaging we are staying close to our previous couple of fcsts, given some fairly reliable guidance still places heavier qpf further north. In addition, CAMs are showing some instability acrs central/southern CWA, which could enhance localized rainfall rates on Monday afternoon into Monday evening. Areal coverage of convection wl decrease on Monday evening with loss of sfc heating, with some areas of fog possible toward Tues morning. Temps mainly upper 70s to mid 80s for Monday and lows mid 60s to lower 70s overnight. && .SHORT TERM /TUESDAY NIGHT/... As of 355 PM EDT Sunday...A few additional showers, initially focused over northern New York and later Vermont, are possible on Tuesday as a weak upper air disturbance slides eastward through the North Country on the backside of a departing trough. Given the moist air mass ahead of this little system, a brief downpour in these isolated to scattered showers is possible, but limited impact is expected. The main idea will be somewhat drier air settling into our region with skies becoming mainly clear. Temperatures will remain warmer than normal with highs mainly in the 80s and lows in the 60s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 355 PM EDT Sunday...The upper level pattern remains active through the long term with the most important player being short wave energy over central Canada midweek. If this energy traverses far enough southward as it nears our longitude, it will help drag a cold front through the region. This scenario continues to be our forecast for Thursday night or Friday morning. Ahead of the front, still will monitor for potential strong thunderstorm activity. Despite some instability, Wednesday looks largely dry with plenty of warm air aloft stifling convection and surface trigger lacking. Timing of a pre-frontal trough with organized convection looks later and relatively unfavorable for thunderstorms late Wednesday night. For Thursday, with the details still fuzzy, it remains a wait-and- see for the mesoscale environment for the favored thunderstorm timing and location. However, the potential is there, as the latest data suggests ample CAPE of greater than 1000 J/kg with greatest instability over southern areas, and favorable shear becomes colocated with this instability late in the day to promote threat of gusty, linear storm modes. Heat index values on both days will again be commonly in the 85 to 90 degree range. While some ensemble members of the GFS continue to keep us warm and humid beyond Thursday, the bulk of the data suggests the front does makes it through and provides seasonable weather for the late week period. The location of an upper level ridge roughly in the mid- Atlantic region will be key to how the weekend unfolds. If it lifts northward, heat and humidity will return, but if it is suppressed farther south, northwest flow aloft will become established which will promote chances of showers but less heat. Generally near normal temperatures are expected with a trend towards more unsettled conditions moving through the weekend. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... Through 06Z Tuesday...Mostly VFR with clouds around 3000-4000 ft agl. Anticipate intermittent MVFR at spots, but not expecting widespread MVFR ceilings. Brief fog possible at MPV between 10Z and 12Z in a brief window of potential clearing, and mentioned a tempo group for 5SM visibility. Winds will be mainly out of the southeast 5 to 8 kts, and gusts will persist at RUT of 15 to 20 kts through about 18Z. Scattered showers will be possible 16Z- 03Z, with the highest chances at RUT and SLK. Beyond 00Z Tuesday, winds will become light and variable. Outlook... Tuesday: VFR. Isolated SHRA. Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. NO SIG WX. Wednesday Night: VFR. Chance SHRA. Thursday: Mainly VFR, with local MVFR possible. Scattered SHRA, Scattered TSRA. Thursday Night: VFR. Scattered SHRA, Scattered TSRA. Friday: VFR. Slight chance SHRA, Slight chance TSRA. && .HYDROLOGY... A Flood Watch is in effect Monday morning through 2 AM Tuesday for Rutland, Windsor, Orange and Addison Counties. There could be a flash flood component. At this time the heaviest rainfall of 1 to 2 inches is expected across central and southern VT, with locally higher amounts near the summits of the southern Greens. The period of potential heaviest rainfall is currently expected to take place Monday afternoon. Our flash flood guidance, indicates the areas most sensitive to rainfall, based on observed rainfall in the past 3 to 6 days would be Essex County, NY into Addison, Washington, and Orange counties in VT. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Flood Watch from 8 AM EDT this morning through late tonight for VTZ009>012-018-019. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Duell/Haynes/Taber SHORT TERM...Kutikoff LONG TERM...Kutikoff AVIATION...Haynes HYDROLOGY...Taber