Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 120803 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 303 AM EST Tue Dec 12 2017 .SYNOPSIS... Deepening low pressure will cross the region today into Wednesday with a widespread moderate to locally heavy snowfall expected. Behind this system chilly temperatures are expected through the end of the week with periodic chances of flurries and light snow, with the best chances occurring later in the weekend. && .NEAR TERM /THROUGH WEDNESDAY/... As of 303 AM EST Tuesday...The forecast remains on track over the next 36-hours as clipper energy tracks from the eastern Ohio Valley through central New England today before exiting into the Maritimes by tonight. All current advisories and warnings remain intact with this package. As discussed quite thoroughly over the last few nights the storm will come in two stages - a warm advection stage today, and an orographic upslope stage later tonight into Wednesday. The overall idea advertises steady light to moderate snow overspreading the entire forecast area through the morning hours before tapering off somewhat later today into the first part of this evening as surface energy and associated isentropic lift exit east. By later tonight into Wednesday the flow transitions to northwesterly allowing a general reblossoming of activity across northern counties, especiallly in favored upslope areas. Snowfall will show considerable variability over any given 6-hour time frame into tomorrow with the proximity of the surface low track allowing a gradual backing of the low level flow over time. That said storm average totals remain largely unchanged and should generally range from 3-7 inches in advisory areas, 5 to 8 inches or so in southeastern VT and the St. Lawrence Valley, and from 6 to 10 inches in the northern Greens. Totals that do fall out of these ranges should be on the order of just an inch or two in the lower elevations and well within a typical standard deviation profile for complex events such as this. Northwesterly winds will also trend quite gusty on Wednesday as p-gradient tightens so this will create areas of blowing snow. High temperatures today should top out in the upper 20s to lower 30s before bottoming out mainly in the teens overnight. Readings won`t really recovery too much on Wedneday under strong cold thermal advection and the aforementioned gusty winds - mainly steady in the mid teens to lower 20s. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/... As of 303 AM EST Tuesday...Light snow and snow showers wind down across the northern mountains Wednesday night before ending by Thursday as high pressure slowly builds into the region. It will remain quite chilly under modestly gusty west/northwest flow with lows Wednesday night in the single digits a highs on Thursday once again in the teens to locally near 20F across the southern valleys. Wind chills Wednesday night look to generally range through the negative single digits to negative teens so slightly warmer than advisory level thresholds - at least that`s the way it looks at this point. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 330 AM EST Monday...Large scale picture shows mid/upper prevailing across the eastern Conus...while energy and moisture from the Pacific NW ejects into the fast flow aloft every couple of days. Latest guidance supports the northern tier staying on the cool side of these systems with several mainly light snow events possible. Below are my daily thoughts for days 4 thru 7. Thursday...deep mid/upper level trof across eastern canada will result in favorable upslope flow...but 1000 to 700mb rh is progged to slowly dissipate by 18z Thurs. Based on llvl caa and upslope flow...expecting remaining moisture to be squeezed out across the northern dacks/greens. Have mentioned chc pops with only minor accumulation expected. Temps aft a chilly start will only warm into the single digits/lower teens mountains to mid/upper teens warmer valleys with brisk northwest winds. Weak surface high pres builds into our cwa on Thurs Night into Friday...but next system approaches our western fa by Friday. Very difficult to determine cloud cover/winds and impacts of fresh snow pack will have on temps Thurs Night/Friday Morning. Have trended toward cooler side of guidance envelope with -10f slk/nek to single digits to around 10f cpv. Some lake effect clouds could impact temps near BTV. Friday/Saturday...Both gfs/ecmwf show next weak clipper like system and associated boundary crossing our cwa. This system will be weaker and have less impact than current clipper. Still anticipating a period of light snow activity...given good 5h energy...some enhanced mid level moisture...and great lake moisture interaction with approaching boundary. Several inches likely in the mountains with a dusting to an inch possible in the valleys. Have continued to mention high chc pops in the grids. Progged 850mb temps btwn -14c and -16c...support highs mainly single digits summits to teens mountain towns to l/m 20s valleys. Sunday...weak mid/upper level ridge and associated 1025mb high pres builds into the ne conus. Extremely difficult to time systems in fast flow aloft...along with amount of clearing and impacts on temps. Have lowered pops slightly for Sunday...but timing of next system could arrive quicker based on fast flow aloft. Clouds and winds will impact temps...but have kept temps close to superblend with lows mainly in the teens and highs in the 20s. Monday...Guidance supports another clipper like system moving thru the Ohio Valley into the NE CONUS. Have noted lots of uncertainty in ensemble data and between 00z/12z guidance in track of surface low...with some to our northwest...while others show a system to our south. Have continued on the cooler side of guidance...thinking surface pres will keep system suppressed to our south...with another light snow event possible. 12z ECMWF shows favorable mid level moisture...good deep layer lift...and moderate llvl waa signature. Plenty of time and uncertainty...so have mention chc pops for now...with temps holding in the 20s. Overall pattern will support a net increase in snow pack across the mountains with cool temps keeping snowpack fresh. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... Through 06Z Wednesday...Deteriorating conditions as moderate snow moves into the region associated with clipper system crossing the area today. Widespread IFR to LIFR develops at all sites by early Tuesday Morning with significant impacts anticipated through 04z, before widespread snow develops from southwest to northeast across our TAF sites between 04z-08z. Visibility will quickly drop to IFR with locally VLIFR in bursts of heavier snow expected at all sites between 09z-15z Tuesday. Ceilings will vary from IFR at MSS to MVFR at RUT/MPV/BTV/SLK/PBG...with periods of IFR possible. Localized southeast winds gusts to 25 to 30 knots at RUT on Tuesday morning with breezy northeast winds at MSS. Conditions will slowly improve at RUT after 18z. Some low level wind shear likely at MSS/MPV with change of speed and direction...causing increased shear and turbulence on Tuesday Morning. Outlook... Monday Night: Mainly VFR, with local MVFR possible. Chance SN. Tuesday: Mainly MVFR, with local IFR possible. Definite SN. Tuesday Night: Mainly MVFR, with areas IFR possible. Chance SHSN. Wednesday: Mainly MVFR, with areas VFR possible. Chance SHSN. Wednesday Night: Mainly VFR, with areas MVFR possible. Slight chance SHSN. Thursday: Mainly VFR, with local MVFR possible. NO SIG WX. Thursday Night: Mainly VFR, with local MVFR possible. Slight chance SHSN. Friday: Mainly VFR, with local MVFR possible. Chance SHSN. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Weather Advisory until 7 PM EST Wednesday for VTZ001- 002-005-009-011. Winter Storm Warning until 7 PM EST Wednesday for VTZ003-004- 006>008-016>018. Winter Storm Warning until 7 AM EST Wednesday for VTZ010-012- 019. NY...Winter Weather Advisory until 7 PM EST Wednesday for NYZ027>031-034-035. Winter Storm Warning until 7 PM EST Wednesday for NYZ026-087. && $$ SYNOPSIS...Deal NEAR TERM...JMG SHORT TERM...JMG LONG TERM...Taber AVIATION...Hastings/Neiles

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