Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 121441 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 941 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/...
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As of 931 AM EST Tuesday...Forecast playing out well this morning with periods of light to moderate snow moving from southwest to northeast across our cwa. Snowfall amounts have ranged from 0.5 to 4 inches so far with highest values over south-central VT and parts of the SLV. Current radar shows another moderate band of snow from near KART to KRME to KALB moving northeast at 15 to 20 mph. Expect this band to produce another quick 1 to 2 inches btwn 15z-18z across our cwa with vis around 1/2sm. Water vapor shows baroclinic leaf developing associated with digging short wave energy and upper level jet over eastern/central PA...which will impact our central/eastern sections this afternoon with additional periods of snow. Very difficult in timing these precip pulses associated with waves of enhanced lift/moisture moving from south to north across our cwa. By this evening a sharp wind shift will occur as sfc low pres jumps to the NH/ME line by 03z. Lots of uncertainty in synoptic and mesoscale models on how much moisture is advected back into the developing llvl caa for a period of upslope snow tonight into weds. We will examine 12z data and make any necessary adjustments with the complete package this aftn. Otherwise...all advisories and warnings look good at this time. Did lower kmss temp by several degrees...associated with ne flow and crnt value only 18f. Rest of fcst looks good. Prior discussion... 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, especially 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 Wednesday under strong cold thermal advection and the aforementioned gusty winds - mainly steady in the mid teens to lower 20s.
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&& .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 Tuesday...Weak ridge of surface high pressure will build over the North country Thursday night and Friday. A weak low pressure system approaches Friday night into Saturday, but only light precipitation is expected for our forecast area. This is another clipper type system, but with less synoptic forcing than the system impacting the area today and tomorrow. From that point on GFS and ECMWF diverge quite a bit. GFS shows yet another clipper system passing north of the area Sun, while ECMWF lacks this feature entirely. Then the ECMWF shows a system moving along the New England coast on Monday night. Overall colder than normal temperatures and active weather pattern is expected. Timing of the different feature is difficult at this time with a lack of model-to-model and run-to-run consistency. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Through 12Z Wednesday...Deteriorating conditions as moderate snow moves into the region associated with clipper system crossing the area today. Widespread IFR to LIFR at all sites with significant impacts through much of the day. Visibility will quickly drop to IFR with locally VLIFR in bursts of heavier snow expected at all sites between thru 15z Tuesday. Ceilings will vary from IFR to MVFR. 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 this Morning. As low passes overhead this afternoon, winds will be light and variable before veering to Northwesterly behind the front. When we have a lull in precipitation ceilings may improve temporarily. 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...JMG NEAR TERM...JMG/Taber SHORT TERM...JMG LONG TERM...Neiles AVIATION...Neiles

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