Area Forecast Discussion
Issued by NWS Burlington, VT

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906 FXUS61 KBTV 171102 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 702 AM EDT Sat Aug 17 2019 .SYNOPSIS... Scattered showers and thunderstorms will redevelop across the region this afternoon, with some strong storms possible containing gusty winds, heavy rainfall, and frequent cloud to ground lightning. The warm and muggy conditions will continue with highs in the mid 70s to lower 80s today. The chances for precipitation will decrease on Sunday, but temperatures will warm into the upper 70s to mid 80s. More unsettled weather is anticipated for early this upcoming week, before cooler and drier air arrives toward the middle of the week. && .NEAR TERM /THROUGH SUNDAY/... As of 654 AM EDT Saturday...Water vapor shows initial 5h vort responsible for showers and storms overnight is quickly exiting our cwa, with just a few lingering showers over the NEK. Meanwhile, already watching an area of showers expanding over western Lake Ontario with general movement toward our SLV zones. Have increased arrival time of chc pops late this morning based on radar trends and latest 10z rap data. This moisture and precip may hinder instability parameters some this aftn, but still expecting a enough breaks for sfc based cape values in the 1000 to 1800 j/kg, especially portions of the central/southern cpv. Areal coverage of convection should increase aft 17z as dynamics arrive with s/w energy. Only other change was to mention patchy fog areawide on Saturday Night/Sunday morning with soundings indicating plenty of leftover bl moisture and lighter wind profiles. Previous discussion below: Active overnight with areas of scattered showers and storms impacting parts of our cwa associated with potent 5h vort lifting across our fa. This activity should continue to impact mainly central/eastern VT thru the next 1 to 3 hours, before moving eastward. Main impacts have been brief heavy down pours and cloud to ground lightning. The challenge today will be how much clearing/instability can develop along with the potential for strong storms. As we have witness all convective season, not all ingredients coming together for widespread/organized severe storms, but expecting some strong convective elements with maybe a severe storm or two. The main uncertainty is how much instability can develop, as soundings show some lingering leftover low to mid level moisture behind departing short wave this morning. This will limit sfc heating this morning, while mid/upper level debris clouds advect toward our cwa this aftn in moderate southwest flow aloft. These different cloud layers will impact sfc heating/instability. However, water vapor does show a potent 5h vort and associated mid/upper level height falls across the central Great Lakes, which will impact our cwa aft 18z today. This energy will interact with moderate instability parameters and modest mid level lapse rates to produce scattered to numerous showers/storms. HREF shows cape values in the 1000 to 1800 j/kg range with highest values in the CPV, while 0 to 6 km shear is in the 35 to 40 knot range. These ingredients combined with height falls associated with vort should be enough to produce strong storms, with a few isolated severe possible. Soundings show steep sfc to 3km lapse rates with good mixing profile and dcape values in the 500 to 800 j/kg range. Thinking as typical the primary concern would be localized damaging thunderstorm wind gusts up to 60 mph in the stronger convective elements. Also, with dynamics and pws in the 1.50 to 1.75 range, localized heavy rainfall is likely in the strongest storms, but storm motions of 20 to 25 knots should limit flash flood threat. Have mention gusty winds/heavy rainfall in grids, which matches well with SPC marginal risk for day 1 outlook. Highs ranging from the mid 70s to lower 80s, given clouds and threat for storms. Tonight, areal coverage/intensity of convection will decrease after sunset with areas of fog/br likely in the deeper river valleys, especially locations that receive rainfall today. Temps mainly in the 60s overnight with some values near 70f cpv. Sunday...weak short wave ridge builds into our cwa, which combined with limited forcing will reduce the chances for showers/storms. In addition, pws drop behind departing s/w energy tonight in the 1.20 to 1.40 range for Sunday, indicating some dry air aloft across our cwa. However, still cannot completely rule out a trrn driven shower/storm, with leftover boundary draped across our cwa and some afternoon instability. Areal coverage will be limited and have kept pops in the 20 to 30% range. Progged 925mb temps range btwn 20-22c, should support highs upper 70s mountains to m/u 80s warmest valleys. Some mixing of drier air aloft is possible per soundings on Sunday aftn, so humidity levels will drop. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... A warm front boundary will move north of the area overnight Sunday into Monday ahead of an approaching front for Monday night. Scattered rain showers are possible during the overnight hours with a slight chance for thunderstorms due to some weak elevated instability. Increasing humidity, southerly flow and clouds will keep nighttime temperatures above average across the area with lows in the upper 60s to low 70s. Temperatures Monday warm into the mid to upper 80s with humid and muggy conditions during the day as dewpoints climb into the mid 60s. Thunderstorms will be possible late Monday afternoon into the evening as the aforementioned front moves across the area. A few things area working against widespread activity... 1) questionable available instability as there will be a lot of junky clouds around Monday morning/early afternoon associated with any overnight rains. If we are able to clear some areas out there will be plenty of CAPE to work with (~1000-1500 J/kg). 2) surface boundary is lifting northward as it passes over area, rather than digging south so best dynamical forcing will be north of the area. And lastly, 3) amount of available moisture along frontal boundary is rather meager. All in all to say, there certainly is the potential for thunderstorms, possible strong/severe given potential available instability and decent shear ~30 but areal coverage and certainty regarding intensity is just too difficult to say at this point. Based off current progs, primary threats with any storms that do develop will be damaging winds and small hail, along with locally heavy downpours. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Period of active weather continues for the long term as several shortwave impulses will pass through the region through middle of next week. Tuesday will bring warm temperatures once again but with lesser humidity values as westerly flow increases across the area. A shortwave moving through the fast flow aloft will pass just south of the area with just a chance for PoPs across our far southern zones...much of the area will stay dry Tuesday. After Tuesday upper level pattern shifts from zonal to a more amplified pattern as a deepening upper level trough develops across the Midwest. Precipitation chances appropriately increase ahead of this feature for Wednesday as broad southwesterly flow advects high PWAT air into New England. Chances for thunderstorms exist Wednesday with shortwave forcing, moisture and CAPE ~1000 J/kg. Relief from the heat and humidity will arrive Thursday with temperatures in the mid to upper 70s. A reinforcing shot of cool air will push through Friday on northwesterly flow aloft. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Through 12z Sunday...Well it was a challenging night in aviation as anticipated with flight categories ranging from vfr to vlifr. Crntly fog with vlifr continues at slk, but has lifted at mss, while ifr cigs prevail at mpv. Thinking fog lifts shortly aft 12z at slk, while ifr cigs linger until 15z at mpv. All sites should eventually become vfr by 15z today with additional threat for showers/storms developing by 17z. Periods of mvfr cigs/vis likely with brief windows of ifr vis possible in the heavier convective elements. Areas of fog with lifr/vlifr conditions likely at slk/mpv by 06z tonight with fog/br possible at most other taf sites btwn 07z-12z Sunday morning, with the combination of plenty of bl moisture and light winds. Outlook... Sunday: VFR. Chance SHRA, Chance TSRA. Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA. Monday: Mainly VFR, with local MVFR possible. Chance SHRA, Chance TSRA. Monday Night: VFR. Slight chance SHRA. Tuesday: VFR. Chance SHRA, Slight chance TSRA. Tuesday Night: VFR. Chance SHRA, Slight chance TSRA. Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA, Chance TSRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Taber SHORT TERM...LaRocca LONG TERM...LaRocca AVIATION...Taber

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