525 FXUS61 KBTV 220149 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 949 PM EDT Sat Aug 21 2021 .SYNOPSIS... Hot and humid conditions continue through tomorrow along with chances for afternoon showers and thunderstorms. The remnants of Hurricane Henri will impact the region late Sunday into Monday and bring the potential for locally heavy rainfall and breezy conditions to portions of the North Country. Heat and humidity remain in place before cooler air arrives by the end of the week. && .NEAR TERM /THROUGH SUNDAY/... As of 944 PM EDT Saturday...No significant changes were needed with this update. The bulk of the showers have dissipated as expected, with just a few rogue cells here and there. Skies are showing some clearing, especially over eastern VT, so patchy fog is still looking like a good possibility in those favored valley locations. Dewpoints are currently in the mid and upper 60s, with even some lower 70s to be seen, and there won't be much change overnight, so it'll be another muggy night. The forecast has this all pretty much covered, so just made some minor tweaks to the PoPs/weather to match the latest radar trends. Previous discussion...Temperatures remain steady in the upper 80s to around 90 across the advisory area, combined with dew points in the low 70s, heat indices in the low to mid 90s (locally higher) have been observed this afternoon. Given this warm and humid airmass, scattered to numerous showers with some embedded thunder have developed along an inverted surface trough which extends from the St Lawrence River into the Gulf of Maine. Main threat continues to be heavy rainfall along with briefly gusty winds, 30 mph or less. These should wane as daytime heating subsides after sunset. Overnight, temperatures remain well above normal in the mid 60s to low 70s. Areas of patchy valley fog/low stratus are also possible as easterly low level flow continues to advect in maritime moisture, especially across eastern VT. Tomorrow will feature a relatively quiet period as high pressure builds in advance of now Hurricane Henri. This should provide the North Country with another hot and humid day, although readings should be slightly "cooler" than today with highs in the mid/upper 80s west of the Greens (heat indices in the upper 80s to around 90) and upper 70s/low 80s for eastern Vermont (heat indices in mid 80s). Much of the area will remain dry, however scattered afternoon showers are possible associated with the outer bands of tropical cyclone Henri for south/central Vermont. The main impacts associated with Henri will occur outside this period. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 416 PM EDT Saturday...Some very minor changes to fcst based on latest guidance, but overall thinking remains the same. Heaviest period of potential rainfall has shifted slightly later Sunday and mainly on Monday, delayed about 6 to 10 hours, but highest qpf totals looks to be from eastern Dacks into central/southern VT. A few outer convective rain bands could impact region as early as 18z Sunday, but not anticipating an issues with these. Based on WPC/NERFC and 12z guidance we continue to fcst qpf amounts of 1 to 2 inches with localized higher amounts possible in stronger/narrow convective bands on Monday for Essex County, NY into central/southern VT, with <1.0 near the International Border. This would be storm total qpf from late Sunday through Monday. As always with slow moving tropical systems the axis of heaviest precip and timing is subject to change moving forward, along with amounts of precipitation. Please continue to monitor latest fcst for potential flash flood watches, as confidence in rainfall and potential impacts becomes clearer. The large scale setup remains very complex with deep mid/upper lvl trof along the eastern seaboard, while sharp/narrow ridge axis remains over northern Maine. This highly amplified and blocking type pattern wl result in Henri coming ashore across eastern Long Island/Southern New England on Sunday aftn/evening and retrograding westward, as system is captured by ulvl trof per NHC fcst. The initial precip shield is progged to impact our southern VT zns Sunday evening, before shifting into western MA/Eastern NY overnight as dry air entrainment wraps into central/northern VT. In addition, the lack of strong poleward jet, wl limit initial expansion of precip northward into our fa, while best llvl forcing associated with 925 to 850mb jet and focus of the heaviest precip axis is located south/southwest of our fa overnight Sunday. On Monday, the combination of mid/upper lvl trof, interacting with pw values of 1.50 to 1.75 and remnants of Henri wl lift acrs our region. Furthermore, timing of these features during peak heating/instability, could result in localized heavy rainfall possible on Monday aftn, acrs portions of our fa. Once again, best ulvl support and llvl forcing looks to be from Essex County, NY into central/southern Vt, where we have the highest precip. Please see hydro section below for additional details. The potential for localized breezy winds have increased slightly on Sunday Night/Monday morning over the higher trrn of Rutland/Windsor counties and western downslope areas of Rutland County. Based on axis of 925mb to 850mb winds of 35 to 45 knots, along with soundings showing some mixing below summit support localized gusts 30 to 40 mph possible. Not expecting widespread issues, but something to monitor. Precip tapers off on Monday night, as mid/upper lvl trof and remnants of Henri shifts east of our fa. A warm and muggy night is likely, along with potential areas of patchy fog with temps mid 60s to lower 70s. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 416 PM EDT Saturday...Another stretch of hot and humid conditions is expected Tuesday through Thursday followed by a return to seasonable and dry weather for Friday and Saturday. Gradually drier air aloft is expected to migrate eastward as weak upper level ridging occurs Tuesday through Wednesday. Therefore, heat will build and skies will trend increasingly clear skies. Precipitation chances are limited to the first part of Tuesday across eastern Vermont. By Wednesday night, there is some indication of a pre-frontal trough arriving from the west which would provide focus for showers and a few thunderstorms. The expected timing will allow for development of quite a bit of convective inhibition, which will limit the thunderstorm threat to western portions of northern New York. Better chances of thunderstorm activity for most of the region will be on Thursday ahead of the surface cold front. At this time, there appears to be ample instability and deep layer shear to support strong to severe thunderstorms, but given the forecast range still more than four days out, a lot can change so we have a broadbrushed chance of thunderstorms across the North Country Thursday through Thursday night before the cold frontal passage. Sharply cooler air will be welcomed into the region Thursday night on seasonably strong northerly flow. Both Friday and Saturday should be seasonable and dry as atmospheric moisture falls a bit below normal for this time of year. As low level flow returns to southerly on Saturday, warmer and more moist air will gradually return. However, it will not become noticeably humid yet. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... Through 00Z Monday...The main feature driving the weather in the next 24 hours will be Hurricane Henri to our south. The system is directing moist onshore southeasterly flow over New England, which will result in increasing low level moisture and some low stratus clouds and/or mist tonight through Sunday morning. Highest confidence in IFR/MVFR conditions at KMPV between 06Z and 13Z, but also thinking KSLK and KRUT will see some lowered flight conditions...although confidence is lower at these sites. Otherwise, mainly VFR conditions expected with just a few lingering showers this evening and again Sunday afternoon. Winds will generally be light and variable. Will see winds from the east increase slightly in magnitude towards 00Z Monday, however most of the more direct impacts from the hurricane won't be felt until after 00Z Monday. Outlook... Sunday Night: Mainly VFR, with local MVFR possible. Chance RA. Monday: Mainly MVFR, with areas VFR possible. Chance RA. Monday Night: Mainly MVFR, with local IFR possible. Chance RA, Chance SHRA. Tuesday: Mainly VFR, with local IFR possible. Slight chance SHRA. Tuesday Night: VFR. NO SIG WX. Wednesday: VFR. NO SIG WX. Wednesday Night: VFR. Scattered SHRA, Isolated TSRA. Thursday: Mainly VFR, with local IFR possible. Chance SHRA, Chance TSRA. && .HYDROLOGY... We continue to monitor the potential for localized heavy rainfall across portions of our forecast area late Sunday through Monday associated with the remnants of Hurricane Henri. At this time the heaviest rainfall of 1 to 2 inches with localized higher amounts looks to occur from Essex County NY into central and southern VT. Current forecasts suggest the period of potential heaviest rainfall is likely on Monday. Our flash flood guidance, indicates the areas most sensitive to rainfall, based on observed rainfall in the past 3 to 5 days would be Essex County, NY into Addison, Washington, and Orange counties in VT. If trends in qpf continue a flash flood watch maybe needed for parts of the area. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...LaRocca NEAR TERM...Hastings/LaRocca SHORT TERM...Taber LONG TERM...Kutikoff AVIATION...Duell HYDROLOGY...Taber