Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 112013 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 313 PM EST Mon Dec 11 2017 .SYNOPSIS... Weak high pressure will bridge across the area today with any morning light snow showers ending and seasonably cold temperatures expected. Low pressure will track across the region on Tuesday and intensify to our northeast on Wednesday bringing a widespread moderate to locally heavy snowfall to our region. Behind this system, a cold airmass settles into the region into Friday before temperatures moderate by next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... As of 204 PM EST Monday... The forecast through this afternoon is playing out largely as expected with just some light flurries across parts of southern Vermont. We`ve even got a few breaks in the cloud cover with some sunshine peaking in here at the office. Cold air advection remains in place with cold air draining in across the valleys. I dont anticipate temps to warm very much and so I`ve adjusted the temps down to max current temps. Prior discussion... The forecast remains largely on track for today as a moderating polar front drops through the area this morning. Scattered light snows/snow showers will continue across mainly central and northern counties in association with the boundary this morning, though accumulations should be light and generally less than an inch. Mainly dry weather is expected across the south. High temperatures will average about 4 to 8 degrees colder than yesterday across the north under light west to northwesterly flow - mainly upper teens to mid 20s, though a few low 30s will be possible far south where the front will arrive later in the morning. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... As of 330 AM EST Monday...The most active period in the 7-day forecast then takes shape later tonight into the Tuesday/Wednesday time frame as a well-advertised clipper low takes a favorable track across our area with a moderate to locally heavy snowfall expected for our area. The low will then deepen rapidly into Wednesday night as it moves to our north and east. As discussed last night, the storm will have two phases, the first occurring Tuesday morning and afternoon as favorable warm advective processes interact with deeper moisture and isentropic lift to produce a widespread moderate snowfall as the low approaches. Southeasterly flow in the lower to mid-levels should allow precipitation to take on a typical orographic character with the heaviest totals along the eastern slopes of the southern Greens where low-end Winter Storm Warnings have been issued for a general 4- 8 inch snowfall. As a side note I`ve leaned on the cooler side of guidance in regard to mid- level warming in these areas and have leaned away from the milder NAM output anticipating wet-bulb processes should be enough to cool the column sufficiently to keep p- type all frozen. Elsewhere, we`re mainly looking at advisory-level totals ranging from 3-7 inches with the highest amounts along the eastern slopes of the northern Greens/Dacks and in the St. Lawrence Valley where where northeasterly channeling may enhance QPF slightly. Lows tonight should generally range through the teens with corresponding highs on Tuesday in the upper 20s to lower 30s. By Tuesday evening the low will track to our north and east dragging the northern nose of a distinct dry-slot into central and southern areas. During this period steadier snows should taper off in intensity and lessen in overall coverage, especially across the south where some patchy freezing drizzle may be possible. At this point it appears there will be a saturated layer above the dry-slot such that light seeder-feeder processes should keep any light pcpn still mainly in the form of light snows/flurries. As we progress into Wednesday phase two of the system affects our area as deeper moisture wraps back into the region on increasingly gusty northwest flow. During this period snows should reblossom in earnest across the northern mountains with some backbuilding into eastern portions of the northern Champlain Valley as flow trends blocked over time. While additional accumulations should be light in most spots, favorable upslope areas of the western slopes and northern Greens stand to pick up several more inches where longer- term Winter Storm Warnings will be in effect, both for the front-end warm advective snows, and the back side upslope phase. Here two-day totals will likely range in the 6-10 inch range with localized heavier totals. With the pressure gradient tightening over time areas of blowing snow will also be possible as northwesterly winds gust into the 15 to 30 mph range. This will put quite the chill in the air and with temperatures holding nearly steady from the mid teens to lower 20s apparent T values will range through the positive and negative single digits. && .LONG TERM /THURSDAY THROUGH MONDAY/...
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As of 312 PM 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 /20Z MONDAY THROUGH SATURDAY/... 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 vifr 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. && .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...JMG LONG TERM...Taber AVIATION...Taber

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