Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 190517 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 117 AM EDT Wed Oct 19 2016 .SYNOPSIS... A weak cold front with scattered showers will cross the area this evening and tonight. The large scale pattern will become increasingly unsettled across the North County by Thursday into Friday as we transition into more seasonable cooler temperatures and showery weather next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... As of 1040 PM EDT Tuesday...Winds will remain moderately strong until cold front pushes through...around 03-04Z for nrn NY and 04-06Z into the Champlain Valley. Looking for a W-NW wind shift with the FROPA, and winds dropping off to 5-10 mph most areas. The lake wind advisory for Lake Champlain has been cancelled. Scattered showers continue to cross the region from W-E...with narrow band of rain along the front extending from Chazy NY to Star Lake NY at 0245Z, moving east around 30kt. Rainfall amounts generally AOB 0.10" (a tenth was recorded at KMSS). Remaining quite warm across wrn VT until FROPA...still 72F at BTV at 0245Z after a high of 81F (25deg above climo avg high). Previous discussion...This evening a weak cold front will approach from the northwest with scattered showers developing along an associated pre- frontal trough across northern NY counties. Hires guidance shows two distinct bands moving through one with the pre- frontal trough and then a second with the actual front. However neither seems to be particularly heavy and so total rainfall across the area will be on the lighter side. Given the upstream conditions and some minor low level instability I did continue to mention the chance for an isolated rumble of thunder across the northern New York areas. Once the front moves into the Champlain Valley the forcing weakens and precip coverage should decline shortly after midnight as front clears south. A weak ridge of higher pressure will begin building in behind the front but the synoptic scale motion remains from the southwest however, so there doesn`t seem as if there will be a significant change in the atmospheric temperatures. Thus I anticipate lows generally holding on the mild side in the 50s to around 60. && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/... As of 327 PM EDT Tuesday...Well advertised large scale synoptic system will produce a long duration and widespread rainfall event across our region starting Thursday morning and continuing into the upcoming weekend. Initially the axis of heaviest rainfall will be located over the Saint Lawrence Valley/Dacks on Thursday into Thursday Night...before shifting into the Champlain Valley and portions of VT on Friday. Models in good agreement with potent 5h energy digging mid/upper level trof across the Ohio Valley on Thursday...which is progged to become negatively tilted and closed off. Meanwhile...a sharp boundary will be draped across our region...with weak 5h short waves moving along this boundary in the southwest flow aloft. Strong low level moisture advection will occur as 925mb to 850mb south jet increases between 35 and 45 knots...with nose of this feature progged over northern NY thru 12z Friday. While right rear quad of 140 knot jet at 250mb is lifting across southern Canada...enhancing deep layer lift. The combination of nearly stationary boundary with strong surface to 925mb convergence and 850 to 700mb fgen forcing...along with pwats surging between 1.25 and 1.75...thinking an axis of moderate to heavy rainfall is likely Thursday afternoon into Friday. Based on moisture and forcing profiles...1 to 3 inches of rainfall will be possible from the Saint Lawrence Valley into the central/northern Dacks by 12z Friday. Meanwhile...a general 0.25 to 0.75" will be expected across northern VT...including the northern Champlain Valley during this time period. Additional rainfall is likely for Friday into Saturday. Expecting a tricky temp forecast for Thursday/Thursday Night...based on clouds/surface boundary and areas of precip. The combination of northeast surface winds and plenty of clouds/precip...have cut guidance by several degrees Saint Lawrence Valley and stayed close elsewhere. Thinking with developing southeast downslope flow...some warming will occur along the western slopes after the progged warm front lifts north of region...but cooler air associated with maritime influence is possible across eastern VT again. Bottom line temps will range from the mid/upper 50s Saint Lawrence Valley/Eastern VT to lower/mid 60s western slopes/champlain valley on Thursday. Little change in thermal profiles expected Thursday Night...with lows mainly in the upper 40s to mid 50s. Localized gusts to 30 knots can be expected along the western slopes on Thursday into Thursday Night...axis of strongest low level winds are expected over northern NY. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 327 PM EDT Tuesday...Potent 5h vort will produce a strongly negatively titled mid/upper level trof...which becomes closed off and vertically stacked with deepening surface low pres by 12z Saturday. The axis of heavy precip will shift from northern NY into central/northern VT late Friday into Friday strong cold front and upper level dynamics pass overhead. This should produce additional rainfall across the Champlain Valley and central/northern Vt of 0.50 to 1.0 thru 12z Saturday. As system becomes vertically stacked and closed off from flow aloft...a prolonged period of upslope precip is expected from Saturday into early next week. How quickly system becomes closed off and how fast it lifts to our northeast into the Canadian Maritimes will determine how much deep Atlantic moisture can advect back into our region. this moisture interacts with cold air advecting on backside associated with brisk northwest winds...our first accumulating mountain snowfall is anticipated by this weekend. GFS is much more robust with deeper moisture...stronger upslope forcing signature and associated heavier qpf fields...why 12z ECMWF shows a shorter duration event with less qpf and forcing...will use blend and mention likely pops over the weekend in the mountains. Additional qpf will be between 0.25 to 0.75 with isolated higher amounts near the summits. Between the synoptic and mesoscale events from Thursday through Sunday...expecting total qpf of 1 to 3 inches across the region with localized higher amounts possible. Given the very dry conditions and long duration event not anticipating any hydro related issues. Snow levels start near summit levels on Friday Night...but as 850mb temps drops below 0c by 06z Saturday and near 2000 feet by 12z Saturday...expect snow levels near 2000 feet by 12z Saturday. These temps profiles support accumulating snow with several inches likely above 2000 feet by 15z Saturday. Favorable upslope winds and moisture continue on Saturday into Sunday with progged 850mb and 925mb temps near 0C...supporting additional accumulating mountain snow. Thinking a few wet snow flakes are possible in the valley floor on Saturday Night...but no accumulation. Given setup and thermal profiles thinking 6 to 10 inches is possible near summits above 3500 feet from Mt Mansfield to Jay Peak and over the Northern Dacks...with 3 to 6 inches in midslope areas...and dusting to 3 inches between 1500 and 2000 by Sunday. These early season mountain snow accumulations are always tricky and complex so stay tuned. Unlike earlier potential events this year...this system will have favorable moisture in the snow growth region and better cold air advection on back side. Otherwise...below normal temps are expected this weekend with highs mainly in the 30s mountains to 40s valleys with lows mainly in the 20s to mid/upper 30s depending upon location. A cold and raw weekend is expected...especially with brisk northwest winds. Temps and conditions slowly improve by early next week as trof lifts. && .AVIATION /06Z Wednesday THROUGH Sunday/...
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Through 06z Thursday...BKN/OVC VFR cigs expected through 12Z with cold front and scattered showers exiting south and east. Only carried showers at KMPV/KRUT early, otherwise dry weather expected. Only exception to VFR will occur at KSLK where MVFR cigs will be likely through 12Z. After 12Z skies gradually trend scattered, then SKC by 00Z. Winds veering to west/northwest from 5 to 10 kts today, trending light and variable by 00Z. Outlook 06z Thursday through Sunday... 06z Thursday through 00z Friday: VFR under weak high pressure. 00z Friday through Sunday: MVFR/IFR as frontal zone and developing low pressure bring widespread showers/rainfall to the area through much of the period. Gusty north winds will be developing on Sunday as well.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Deal NEAR TERM...Banacos/Deal SHORT TERM...Taber LONG TERM...Taber AVIATION...JMG/Evenson is the U.S. government's official web portal to all federal, state and local government web resources and services.