Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 112107 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 407 PM EST Mon Dec 11 2017 .SYNOPSIS...
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A strong clipper low pressure system is expected to bring widespread moderate to heavy snowfall across northern New York and Vermont. Winter Storm Warnings and Advisories are in effect for Tuesday and Wednesday. An arctic airmass will move in behind the low pressure system bringing cold temperatures through Friday before warming slightly over the weekend.
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&& .NEAR TERM /THROUGH TUESDAY/...
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As of 401 PM EST Monday...Winter Storm Warnings and Winter Weather Advisories are in effect for the North Country as clipper low is expected to bring significant snow to the region. The rest of this evening should be fairly quiet as high pressure to our north continues to pull away from the region as a clipper digs south of the Great Lakes. Cold air is still draining into the Champlain and Saint Lawrence Valleys with mid 20s across the northern tier of Vermont and most of northern New York. Expect overnight lows to fall into the teens early this evening before southerly flow sets in. Once southeasterly flow ramps up, as the clipper starts to move into region, warm air advection will surge into the region. Warm advection snow will push into northern New York and into Vermont during the overnight hours. The trends in the near term guidance continue to point to significant snow accumulating across most of the North Country. Omega in the snow growth zone amplifies with nearly 100% saturation in the DGZ which all points to moderate to heavy snow across the North Country. As the midnight shift described, the storm will move through in two waves with significant differences in the locations of snow accumulations. With the first warm advection snow, expect strong south to southeasterly winds to push into the region which will cause downsloping effects in the western Greens and Adirondacks. These areas will be the last to see accumulating snow and likely to see only see 3-6 inches initially whereas the eastern slopes of the Greens and across the Saint Lawrence valley will see 6-10 inches. The closed surface low looks to drop just south of the forecast area which will lead to the dry slot perhaps not making it all the way into the North Country. With the location of that low track and the warm air advection all day, is possible in the southern Champlain Valley and Connecticut river valley that the temperature profile will warm up enough to see some rain mix in but for the time being I haven`t included that in the forecast. The second phase is the orographic snow described in the Short Term.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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As of 401 PM EST Monday...The second phase of the system will come Tuesday night into Wednesday as the low pulls into Northern Maine. Cold air advection returns and the flow on the backside of the low turns northwest. Once this happens we`ll move into a more favourable upslope pattern where the western slopes of the Greens and Adirondacks start to pick up some bigger numbers. Froude numbers initially will be blocked Tuesday night into Wednesday and so the snow should back up into the Champlain valley. Expect during this second phase that the upslope regions will pick up another 3-6 inches of snow while the rest of the North County sees an additional 1-2 inches. The flow aloft picks up fairly quickly during the day on Wednesday and the flow becomes unblocked so we`ll be looking at the potential for some blowing snow across northern New York with accumulating snow moving back into the Northeast Kingdom. Its going to be rather chilly on Wednesday as cold air advection rips into the North Country. Expect highs in the teens across Northern New York and in the low 20s across Vermont. With gusty winds its going to be quite the shock to the system to feel wind chills back into the single digits above and below zero. Some lingering mountain snow showers will continue in the evening hours on Wednesday however the flow will be turning more west to west northwesterly so with cold air and flow across warm lakes we`ll be switching gears to a lake effect snow again. Most of the accumulating lake effect snow will fall south of Saint Lawrence county. Across the North Country, with a fresh snow pack and cold air still pushing into the region expect a chilly evening with lows in the single digits above and below zero.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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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 mtn 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.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/...
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Through 18Z Tuesday...Widespread ifr to lifr develops at all sites by early Tuesday Morning...with significant impacts anticipated to the aviation community. Meanwhile...VFR conditions at mss/slk/pbg with intervals of mvfr cigs/vis thru 20z at rut/btv and mpv in light snow. Expecting mainly vfr conditions from 20z- 04z this evening...before widespread snow developed from southwest to northeast across our taf sites btwn 04z-08z. Vis will quickly drop to ifr with locally vlifr in bursts of heavier snow expected at all sites btwn 09z-15z Tuesday. Cigs 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 Rutland on Tuesday morning with breezy northeast winds at MSS. Vis/cigs will slowly improve at rutland aft 15z. 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.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Weather Advisory from 1 AM Tuesday to 7 PM EST Wednesday for VTZ001-002-005-009-011. Winter Storm Warning from 1 AM Tuesday to 7 PM EST Wednesday for VTZ003-004-006>008-016>018. Winter Storm Warning from 1 AM Tuesday to 7 AM EST Wednesday for VTZ010-012-019. NY...Winter Weather Advisory from 1 AM Tuesday to 7 PM EST Wednesday for NYZ027>031-034-035. Winter Storm Warning from 1 AM Tuesday to 7 PM EST Wednesday for NYZ026-087. && $$ SYNOPSIS...Deal NEAR TERM...Deal SHORT TERM...Deal LONG TERM...Taber AVIATION...Taber

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