Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 230719 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 319 AM EDT Tue May 23 2017 .SYNOPSIS... A weak cold front crossing New York and Vermont through this evening will bring isolated showers, along with lingering low clouds and areas of fog overnight. Will see clearing Tuesday with a weak area of high pressure in place across the northeastern U.S. and temperatures moderating back into the upper 60s to lower 70s. A few afternoon showers are possible Wednesday, but high temperatures will continue to moderate into the low to mid 70s. A large mid-level trough across the Tennessee and Ohio Valleys and associated developing surface low pressure will bring increasing chances for widespread rainfall across the North Country on Thursday and Friday. && .NEAR TERM /UNTIL 2 PM THIS AFTERNOON/... As of 702 PM EDT Monday...Minor adjustments to the previous forecast for this evenings update, mainly to reduce pops and tweak sky cover. Frontal showers have quickly exited the region to our east, and while a few stray showers may be around through the evening, in general the remainder of the night will be dry. Forecast challenge for sky cover remains though with subsidence building in aloft and an abundance of low level moisture around. Current thinking is that sky cover will be widely variable through the night with some low stratus hanging tough over higher elevations, while many valley locales may clear out to a scattered/overcast mid/high deck. Can`t rule out some areas of fog, especially in any clearing so have left that in, but signals are trending towards less of a chance of dense fog and more BR-ish with winds just off the deck hanging in the 10-15 knot range. Lows remain on track for mid/upper 40s to low 50s. Previous Discussion... Will see some gradual mid-level drying this evening (above 750mb) with WSWLY flow aloft, but pronounced low- level inversion should continue to hold low stratus in areawide with overcast skies and cool temperatures. Afternoon highs only expected to range from the lower 50s east of the Green Mtns, to near 60F at BTV, and upr 50s to lower 60s across nrn NY. The KCXX vad wind profile still indicates 25-30kt flow at 2-3kft AGL. Won`t fully see these winds at low elevations due to stability, but occasional gusts to 20-25 mph are possible thru this aftn. Expect winds remaining 20-25kts over the broad portion of Lake Champlain, and the Lake Wind Advisory continues there. Tonight through Tuesday a weak surface ridge builds into the region. Lowering inversion and light surface winds, along with moist ground from recent rain will promote fog formation in the usual areas. During this time flow aloft remains southwesterly, and low pressure over the Great Lakes will ride through the 500 mb ridge, suppressing the ridge & shifting it east. The low passes well enough north that the surface ridge will win out with no rain during this time, but will still be quite a few clouds around. Tuesday about 10 degree warmer than monday with highs in the 60s/near 70. && .SHORT TERM /2 PM THIS AFTERNOON THROUGH THURSDAY/... As of 315 PM EDT Monday...12z guidance suite still indicating that Wednesday will be the warmest day of the entire weak. Weak ridging aloft will put the region into a col area (light flow regime). Hi-res models do hint at just enough low level moisture and surface instability will exist to pop a few showers, primarily across the higher terrain in the afternoon, though with an inversion around 15,000ft not expecting any t-storms to develop. Winds from 10,000ft down to the surface will be generally 10 knots or less, so look for onshore lake breezes to develop. 925mb temperatures will be running about 17C, which given a decent amount of sunshine will result in lower elevation temperatures within a couple of degrees of 80F. Wednesday night flow starts to turn south/southeast as low pressure moves toward the Great Lakes. Models all show an area of deeper moisture moving toward the region, so as we move toward daybreak Thursday it appears precipitation will be starting to overspread the region. Have depicted a ramping up of PoPs up well after midnight, though most of the night will be dry. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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As of 259 AM EDT Tuesday...New 00z guidance showing some disagreement with evolution of closed mid/upper level trof and associated surface low pres. GFS shows a track further east with limited qpf Thursday Night into Friday...while ECMWF shows a negatively tilted and vertically stacked system moving from the Mid Atlantic into Southern New England during this time period. Both agree on precip across our cwa...but exact details on placement of heaviest precip axis and associated pops still has some disagreement. Will continue to mention high likely to low cat pops for Thursday Night into Friday (65 to 80%)...with highest values central/eastern cwa. Expecting a similar type scenario for qpf...as nose of easterly 925mb to 700mb jet is angled toward our eastern zones...helping to enhance moisture advection off the Atlantic. Speaking of Atlantic...expecting a chilly maritime airmass over our cwa during this time period and have cut superblend temps by 2 to 4 degrees...especially eastern/central cwa. The combination of cooler easterly flow...lots of clouds/precip...and progged 925mb temps btwn 6-8c support highs mid 50s to mid 60s. Warmest temps will be western dacks/SLV. For the weekend...weak 1013mb high pres builds into the North Country for Saturday...with still some embedded short wave energy and moisture with westerly flow aloft impacting our northern zones. The combination of lingering moisture...upslope flow...and weak energy aloft...cannot rule out a few midday showers...especially central/northern cwa on Saturday. 925mb to 850mb thermal profiles support highs very close to normal with mid 60s to mid 70s depending upon elevation and cloud coverage. For Sunday...still some uncertainty on placement of weak backdoor cold front or developing warm front lifting from southwest to northeast across our region. This weak convergence with embedded energy aloft may provide enough lift to support a few afternoon showers. Instability is limited and displaced to our southwest...so not anticipating any thunder threat. Have continued to mention slight chance to chance pops...with threat increasing during the afternoon hours. In addition to precip uncertainty...still some question on max temps for Sunday...with a wide range in thermal profiles. We will stick close to superblend values...which is consistent with previous couple of forecasts. Highs mainly in the upper 60s to mid 70s...with 74 expected at BTV. Even more uncertainty as we head into early next week...associated with additional energy aloft and timing of another surface cold front. Latest ECMWF shows several boundaries lifting across our region with numerous embedded vorts in the flow aloft...along with ribbons of enhanced mid level moisture. Initially instability is limited...but increases some on Tuesday to support a chance of thunder. Will continue to mention chance pops with near normal temps...as we have plenty of time to work out the details in the upcoming days. Bottom line not expecting any long windows without the chance for rain and no significant heat in days 4 thru 7.
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&& .AVIATION /07Z TUESDAY THROUGH SATURDAY/... Through 00Z Wednesday...A challenging aviation forecast continues thru 12z this morning with fog product and obs showing multi cloud layers with categories ranging from ifr at rut/mpv to vfr elsewhere. Thinking ifr conditions become mvfr/vfr at rut/mpv shortly as winds help with mixing. The combination of yesterdays rainfall and lighter winds after 08z...and several locations going 3 to 6 degrees below cross over temps...thinking some fog/br will develop between 08z-11z. Have utilized tempo group at rut/mpv and slk to highlight fog/br potential early this morning. Overall confidence in IFR potential is on the low side...given 10 to 15 knots of winds around 975mb. After 12z...expecting cigs/vis to become VFR with winds shifting to the north at 4 to 8 knots...with some localized terrain driven gusts. Some high clouds possible today as coastal system passes to our east. Outlook... Wednesday: VFR. NO SIG WX. Wednesday Night: VFR. Chance SHRA. Thursday: VFR. Breezy. Likely RA. Thursday Night: MVFR with areas of IFR CIGS MPV. Breezy. Likely RA. Friday: MVFR with IFR MPV/SLK. Likely RA. Friday Night: VFR. Chance SHRA. Saturday: VFR. Slight Chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...Banacos SHORT TERM...Nash LONG TERM...Taber AVIATION...Taber

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