Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 180846 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 346 AM EST Mon Dec 18 2017 .SYNOPSIS... Surface high pressure cresting over the North Country will bring seasonably cold and quiet conditions through the first half of tonight. A warm front approaching from southwestern New York will bring increasing cloudiness and widespread light snow for Monday morning into early Monday afternoon. Snow accumulations between 1 and 3 inches are generally expected, with localized totals around 4 inches for the southern Green Mountains. A brief warm up is expected on Tuesday, with gusty south to southwesterly winds. A frontal passage Tuesday evening will bring a few rain or snow showers and a return to colder temperatures. The next chance for significant precipitation will arrive Friday night into Saturday. A low pressure system passing to the west of the region is expected to bring mixed wintry precipitation, transitioning to plain rain as warmer air moves in on southerly winds. && .NEAR TERM /THROUGH TUESDAY/... As of 933 PM EST Sunday...Once again just dealing with temperatures as light winds and only thin high level clouds exist over the area. This is allowing temperatures to continue falling tonight...but thicker cloud cover will move in after midnight and temperatures should level off or slowly rise toward morning. Rest of forecast in good shape with light snow eventually getting into our area toward the morning commute. Previous Discussion... A period of light snow 12-18Z Monday will produce a general 1-2" snowfall across the region, with localized totals 2-4" across the spine of the Green Mtns and across portions of southern St. Lawrence and Franklin NY counties. While not a significant event, may see a few travel slowdowns across the region Monday morning into early Monday afternoon with snow covered roads and brief periods of visibility less than one mile. We`ve made this the focus of our social media posts this afternoon and included mention in the Hazardous Weather Outlook. In the meantime, looking at a quiet evening and first half of the night as 1030mb sfc anticyclone crests over the North Country and srn Quebec before shifting ewd. This will result in light winds and good radiational cooling after sunset. By midnight, should see 2-meter temperatures generally zero to 10 above, and locally falling below zero across far nern VT. Will see temperatures level off after 06Z Monday - or rise slightly - with increasing high- mid level clouds from SW-NE in advance of modest warm front across the srn tier of NY. Likewise, light S-SE winds will develop after midnight. Should see sufficient isentropic lift to allow light snow to develop starting around 11Z across the nrn Adirondacks and Rutland county, and lift nwd into the Champlain Valley by 12Z or so. Combined with modest mid-level height falls as a shortwave trough progresses ewd along the intl border, will see a widespread light snowfall across the area thru 18Z or so. With warming aloft, will see snow-to-liquid ratios drop into the 12:1 to 14:1 range. Best forcing for ascent shifts ewd during Monday aftn, with some continued orographic snow in the Green Mtns and across the Adirondacks. Temperatures will not be as cold, with highs Monday generally 25-30F, except lower 20s with localized nely winds in the St. Lawrence Valley, and across far nern VT where low-level cold air will be slower to scour out. Monday night will feature continued overcast conditions and light S-SW winds, increasing a bit toward daybreak Tuesday (5-10 mph). Temperatures will hold relatively steady in the mid- upr 20s and slowly rise to near freezing by daybreak Tuesday. Not much large- scale ascent, but continued light precipitation across the nrn Adirondacks and nrn Greens will remain possible with sw low-level flow and orographic ascent. Slowly warming thermodynamic profiles may allow for intervals of sleet or even plain rain in swrn St. Lawrence county. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 316 AM EST Monday...Large scale pattern shows developing mid/upper level trof with weak sfc boundary passing across our fa. The combination of caa...upslope flow...good 5h energy...and some leftover moisture will result in a period of accumulating snowfall across the dacks/green mountains Tues Night into Weds. 925mb temps near 0c at 00z Weds...support mainly rain valleys with snow levels btwn 1500-2000 feet...but quickly dropping to the valley floors by 06z Weds...as 925mb temps cool. Have mention likely to cat pops from northern Dacks into the central/northern Green mountains for Tues Night into Weds Morning...with 3 to 5 inches of snow accumulation possible. Meanwhile...westerly flow and warm boundary layer temps will limit accumulation across the cpv and ct river valleys to an inch or less. Have kept pops in the schc/chc range. 1030mb surface high pres builds into our cwa on Weds into Weds night...with west/northwest flow continuing. This results in deep layer drying...along with progged 850mb temps dropping btwn -14c and -16c by 12z Thursday. These thermal profiles suggest steady or falling temps on Weds...under brisk winds. Thinking lows mainly mid 20s to lower 30s by Weds AM...with highs mainly in the 20s to lower 30s Weds...before dropping into the single digits above and below zero. Still some question on snow pack and winds...so have stayed close to guidance...which has been too warm lately with lows in the deeper protected valleys. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 316 AM EST Monday....1030mb high pres provides cwa with a chilly but dry day on Thursday...with progged 850mb around -15c. Highs mid teens to lower 20s with light northwest winds. Thursday Night...temps will be tricky as latest 00z ECMWF shows 850 to 500mb moisture streaming from west to east across our fa...along with increasing winds aft 06z Friday. Thinking temps fall quickly early Thurs evening...before increasing aft 06z...with clouds/winds developing. Lows ranging from -5 to -10f NEK/SLK to 5 to 10f cpv/slv. If skies are clear and winds stay light...these temps will be much colder. Next large scale synoptic system will impact our cwa Friday into Saturday...as mid/upper lvl trof deepens across the central Plains and sfc low pres develops. Models in good agreement with sfc low pres tracking across the MS Valley into the central Great Lakes by 12z Saturday...placing our cwa well established in the warm sector. However...1030mb high pres over northern ME will produce the classic cold air damming signature with cold air remaining locked in the deeper valleys of eastern/central VT late Friday into Saturday...even with progged 850mb temps warming to 6c. Latest trends show a series of warm fronts and associated ribbons of enhanced 850 to 700mb lift/moisture impacting our cwa. Initially thermal profiles support all snow late Friday aftn/evening with first surge...however developing southwest 850mb jet of 55 to 65 knots will quickly warm 925mb to 850mb layer above 0c by 12z Sat. Meanwhile...cold air will remain trapped in the northern SLV and parts of central/eastern VT...especially ct river valley/nek with areas of sleet/freezing rain likely. An advisory level event with some ice accumulation looks likely at this time...given available moisture/lift. QPF with southwest orientation of llvl jet will be terrain influenced...with typical shadowing here in the cpv off the high peaks. Difficult to determine amount of low level mixing with shallow inversion and potential for gusty winds at this time. Highs Saturday will range from the mid/upper 30s colder valleys of eastern VT to lower/mid 50s CPV/parts of the western dacks...thinking all locations briefly break into warm sector with better mixing prior to fropa late Saturday into Sunday. Sharp boundary sweeps across our fa with a period of rain showers...changing to mountains snow showers by 12z Sunday. Limited accumulation with developing dry slot behind fropa. Temps mainly in the upper 20s to mid/upper 30s on Sunday with a few leftover mountain snow showers possible. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Through 06Z Tuesday...VFR conditions will exist through about 09z with only mid and high level clouds over the area. Eventually after 09z a warm front will approach from the southwest and ceilings will lower into the MVFR category with light snow developing as well. The snow will reduce visibilities into the MVFR and IFR categories between 12z and 18z...then improve back into the VFR category for the remainder of the period. Ceilings however will remain in the MVFR category for the remainder of the period, lowering to IFR at SLK late. Winds will generally be variable and under 10 knots through about 18z before become south for the remainder of the period. Outlook... Tuesday: Mainly MVFR, with areas VFR possible. Chance SHRA, Chance SHSN. Tuesday Night: VFR. Chance SHSN, Chance SHRA. Wednesday: Mainly VFR, with local MVFR possible. Slight chance SHSN. Wednesday Night: Mainly VFR, with local MVFR possible. NO SIG WX. Thursday: Mainly VFR, with local MVFR possible. NO SIG WX. Thursday Night: VFR. Slight chance SHSN. Friday: Mainly VFR, with local MVFR possible. Chance SN. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Banacos NEAR TERM...Banacos/Evenson SHORT TERM...Taber LONG TERM...Taber AVIATION...Hastings

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