Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 180549 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 149 AM EDT Thu May 18 2017 .SYNOPSIS... Near record high temperatures expected on Thursday, along with gusty southwest winds, especially the Saint Lawrence Valley. The heat will help to fuel strong to locally severe thunderstorms late Thursday afternoon into the overnight hours. The primary threat will be damaging winds and one inch hail. Much cooler and drier weather returns to the North Country on Friday into the upcoming weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... As of 1014 PM EDT Wednesday...Continued the idea to slow down how quickly temps fall this evening as its 10 PM and its still 80 degrees in Burlington and Plattsburgh with mid 70s across the North Country. Given this I did bump up overnight lows by a degree or so which does keep BTV in line to set a record high minimum temperature for May 18th. The record high minimum temperature is 63 degrees set back in 1936 and based on the current forecast would be broken by 3-4 degrees. Boundary heights haven`t fallen as quickly either and so some gusty winds remain however over the next 2-3 hours most of the winds should decouple and quit gusting. Previous discussion...A quiet night anticipated as cwa is directly under mid/upper level ridge and deep dry layer aloft. Expecting some upstream convective debris clouds to advect around the ridge and provide our fa with some mid/upper level cirrus and maybe a sprinkle. Soundings support some mixing of winds in the wider valleys, like the CPV/SLV and combined with dwpts climbing into the mid 50s to lower 60s...will cause much above normal temps overnight. Lows mainly 50s protected valleys to l/m 60s cpv/slv. Southwest winds 5 to 15 mph...depending upon location. && .SHORT TERM /6 AM THIS MORNING THROUGH FRIDAY NIGHT/... As of 313 PM EDT Wednesday...Still anticipating a very active period of weather with near record temps...gusty winds...and strong to locally severe thunderstorms Thursday into Thursday night. Synoptic scale setup shows mid/upper level ridge breaking down as initial pre-frontal trof and embedded leftover convective debris vort approaches our cwa btwn 18z-21z Thursday. Meanwhile...the stronger mid level energy and better low level surface convergence is located over the central Great Lakes into southern Canada. Strong 925mb to 700mb southwest flow of 45 to 60 knots will help to advect deep layer moisture into our region...along with very warm temps. Progged 925mb temps range between 22c and 24c on Thursday supporting highs mid 80s to lower 90s with surface dwpts climbing into the upper 50s to l/m 60s. (Already lower 60s across the SLV). This heat and low level moisture will produce surface based CAPE values between 1200 and 1800 j/kg Thursday aftn with 0 to 6 km shear values of 45 to 55 knots. Soundings show mainly unidirectional flow from sfc thru 500mb with expected storm motions of 45 to 50 knots. Our current thinking scattered convection develops along lake breezy boundary off Lake Ontario around 20z...with some additional storms possible firing off the higher terrain of the dacks and moving into VT during the late aftn/early evening. These airmass type storms will have the potential for gusty winds and hail...given instability and wind profiles...but may lack organization due to the limited large scale lift. This idea is supported by the local 4km and latest 3km NAM outputs. Meanwhile...a line of strong to severe storms with the primary threat being gusty winds will be approaching the SLV by 00z Friday. Given the very strong low level wind fields (50 knots at 925mb)...and better dynamics/surface convergence...thinking this convection will start as discrete mini supercells over southern Ontario and evolve into a line of storms over the SLV/Northern NY between 23z-03z. Very difficult to determine if this line of storms holds together across the CPV...given timing and still some uncertainty about impacts from cooler Lake Ontario environment stabilizing low level airmass. SPC day2 of slight risk looks reasonable and will continue with enhanced wording in the zones and may freshen up HWO with afternoon package. Latest NAM3km and BTV 4km continue to show a ribbon of very strong 925mb to 850mb winds of 45 to 55 knots channeling up the SLV between 18z and 03z on Thursday. Soundings continue to shows bottom of mixed layer values between 35 and 40 knots...with some enhanced channeling associated with sw to ne orientation supporting localized gusts between 45 and 50 mph. Will issue advisory from 18z to 03z for SLV with potential for some isolated power outages and trees down. Friday into Friday Night...Much cooler on Friday with strong llvl caa developing on brisk northwest winds. Soundings continue to show plenty of moisture between 925mb and 700mb thru 18z for CPV and 00z for the mountains of central/northern VT...so expect lots of clouds with some upslope/terrain driven showers. Depending on position of actual surface cold front...so scattered showers are possible over eastern/southern VT during the morning hours. Will mention chc to likely pops with highs only in the mid 50s to lower 60s. Surface high pres builds into cwa on Friday night with clearing skies and light winds...expecting areas of frost in deeper/protected valleys of the dacks/northern VT. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 321 PM EDT Wednesday... High pressure will continue to build into the North Country over the weekend and the outlook is quite pleasant for any weekend activities. Guidance remains consistent with the idea that an upper level low and corresponding surface low will track up through the Great Lakes. This will eventually swing a surface front through the North Country some time on Monday. Timing on that front has been varying from model to model and run to run however with the lack of much warm air, I dont anticipate to much in the way of thunderstorm activity at the moment. However as the previous forecaster mentioned, there will be abundant moisture and so some locally heavy rainfall will be possible with those showers. Behind that front dry air moves in again as high pressure builds from the west and the outlook for early week looks pleasant again with near normal temps. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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Through 06Z Friday...VFR conditions persist throughout the period. Low level wind shear continues this morning before sunrise and mixing begins to produce wind gusts of 20 to 30 kts...possibly around 40kts in the Saint Lawrence Valley during the afternoon hours. Daytime heating and abundant moisture likely to result in instability and rain showers during the early afternoon. Have included VCSH at this point. Thunderstorms may develop with these showers associated with lift of prefrontal trough. A cold front moving across the North Country during the evening hours may lead to more widespread showers and thunderstorms. Outlook... Friday: VFR. Breezy. Chance SHRA. Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. Chance SHRA. Sunday Night: VFR. Chance SHRA. Monday: MVFR. Chance SHRA.
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&& .CLIMATE... Max Temp Records for Today 5/17/17 KBTV...90 set in 1977* KMPV...85 set in 1977 K1V4...88 set in 1991 KMSS...88 set in 1962 *BTV has already reported 91F and thus broke the record. Max Temp Records for 5/18/17 KBTV...89 set in 1989 KMPV...90 set in 1962 K1V4...92 set in 1906 KMSS...90 set in 1962 && .EQUIPMENT... The WSR-88D at Fort Drum (KTYX) will be unavailable through Thursday May 18, 2017. During the outage, radar coverage is available from adjacent radar sites including Burlington (KCXX), Albany (KENX), Buffalo (KBUF), and Binghamton (KBGM). A new signal processor will be installed, which replaces obsolete technology, improves processing speed and data quality, provides added functionality, and supports IT security. && .BTV WATCHES/WARNINGS/ADVISORIES...
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VT...None. NY...Wind Advisory from 2 PM this afternoon to 11 PM EDT this evening for NYZ026-027-087.
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&& $$ SYNOPSIS...Taber NEAR TERM...Deal/Taber/Hanson SHORT TERM...Taber LONG TERM...Deal AVIATION...KGM CLIMATE...WFO BTV EQUIPMENT...WFO BTV

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