Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 201740 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 140 PM EDT Tue Aug 20 2019 .SYNOPSIS... Showers and thunderstorms return Wednesday afternoon with the potential for some organized storms capable of gusty winds, locally heavy rainfall, and frequent lightning. A cold front will push through Thursday morning, followed by high pressure building in and a return to cooler and drier weather for the end of the week. && .NEAR TERM /THROUGH WEDNESDAY/... As of 943 AM EDT Tuesday...North Country Chamber of Commerce weather today with plenty of sunshine and mild temperatures, along with lower humidity levels. A weak cold front has passed through our cwa overnight, resulting in advection of drier and slightly cooler thermal profiles. Highs today generally in the mid 70s to lower 80s, maybe a few mid 80s cpv, given deep mixing with such dry profiles. The aforementioned cold front will lift back north as a warm front late tonight into early Weds. This boundary, along with some increase mid level moisture and weak embedded 5h vort sliding across our fa, may produce just enough ingredients for a few showers/embedded storms. Have pops increasing to chc by 12z Wed with some isolated mention of thunder, due to increasing instability parameters above shallow inversion. Temps tonight mainly in the upper 40s to l/m 60s with comfortable humidity values. Expecting an active Weds with development of showers and thunderstorms likely during the aftn/evening hours. SPC has placed most of our cwa in slight risk for severe, but still some uncertainties on degree of instability and limited convergence as a series of boundaries swing across our fa. It seems ingredients look very favorable a day or two out, but when event is here, several factors combine to limit the intensity and coverage of storms of so far this convective season. Thinking warm front lifts north of cwa by 15z, with most of our region well established in the warm sector with climbing bl temps/dwpts. Temps will warm well into the 80s with dwpts approaching 70f in the slv/cpv by mid aftn. This will help to destabilize our atmosphere with sfc based cape ranging from 1500 to 2500 j/kg, with highest values in the CPV on Weds aftn. Meanwhile, developing low level jet of 25 to 30 knots, along with increasing 700 to 500mb wind fields from approaching mid/upper level trof will enhanced favorable 0 to 6 km shear of 35 to 45 knots. These ingredients all support severe storms with some organization on Weds, along with sounding data indicating an EML of 6 to 7 C/km lapse rates btwn 700 and 500mb. Furthermore, good height falls are expected with approaching trof. However, still some uncertainty on amount of sfc instability due to potential clouds and limited low level forcing, as a series of boundaries will be crossing our cwa. The 00z NAM NEST composite reflectivity progs are not all that impressive across our cwa either, but ARW and HRW WRF NSSL are much more robust, indicating the potential for strong/severe storms. Sounding thermodynamics and wind profiles would support some organized convection with bowing line segment/multi-cell convective mode. Gusty to localized severe winds would be primary threat, with some low level turning of profiles, especially where trrn (SLV/CPV) influences the local wind direction. Have mention potential threat in HWO for now, but given uncertainty on forcing and instability have not placed enhanced wording in forecast yet. Still plenty of time for dayshift or mid shift to add wording and fine tune location/timing of convection in the next 12 to 24 hours. As with any convection, localized heavy rainfall and frequent lighting is anticipated with any storms on Weds. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 320 AM EDT Tuesday...The main weather feature for Thursday will be the passage of a cold front associated with a deepening low pressure system across Quebec. Still some timing differences among the models on when the front will pass with ECMWF slowest of the solutions and GFS the fastest. Have settled on a blend between the two, very similar to NAM timing with FROPA arriving between 12-18z from west to east. Winds aloft will turn out of the west advecting in lower dewpoints but better cold air advection does not arrive until overnight Thursday into Friday with the passage of a secondary cold front. Temperatures Thursday will still be ~6-10 degrees cooler from Wednesday with highs in the mid 70s mountains and St Lawrence Valley to around 80 elsewhere. As mentioned by previous forecaster the passage of this front should be relatively uneventful with some showers and possibly isolated embedded thunderstorm. Model progs indicate very narrow band of moisture with this feature and weak elevated instability and meager SB CAPE around 300-600 J/kg. Have generally offered 30s-50s PoPs with highest chances across St. Lawrence valley and International Border with lowest chances for our southern counties. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 320 AM EDT Tuesday...No real changes made to the extended forecast with upper level troughing remaining in place through Friday/Saturday. Secondary cold front and reinforcing shot of cold air arrives Friday with a slight chance of showers possible across the northern mountains and Northeast Kingdom of Vermont. Partly cloudy skies are expected with temperatures topping out in the mid 60s to around 70. Overnight lows will drop below normal into the mid 40s to mid 50s. Similar conditions are expected for Saturday under mostly sunny skies. After this, upper level pattern becomes highly amplified across the eastern US with high pressure and dry weather expected trough midweek. Temperatures warm a couple degrees each day with near normal highs in the mid 70s to around 80 to lows in the low to upper 50s. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Through 18Z Wednesday...High pressure in control supplying VFR flight conditions through 12Z. High and mid-level clouds will overspread the region after 06Z as a warm front moves through, which should limit fog potential overnight. Will see clouds lowering and some vicinity showers develop after 12Z, with some thunderstorms possible after 16Z. The best potential for thunderstorms exists after 18Z however, so have left any mention of thunderstorms out of this TAF package. Outlook... Wednesday: VFR. Likely SHRA, Chance TSRA. Wednesday Night: Mainly VFR, with local MVFR possible. Chance SHRA, Slight chance TSRA. Thursday: Mainly VFR, with local MVFR possible. Chance SHRA. Thursday Night: VFR. Slight chance SHRA. Friday: VFR. Slight chance SHRA. Friday Night: VFR. NO SIG WX. Saturday: Mainly VFR, with local MVFR possible. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Duell/Taber SHORT TERM...LaRocca LONG TERM...LaRocca AVIATION...Duell

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