Area Forecast Discussion
Issued by NWS Burlington, VT

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183 FXUS61 KBTV 040800 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 300 AM EST Sun Dec 4 2016 .SYNOPSIS... Cloudy skies and lingering morning flurries will give way to partial sushine by later today as weak high pressure bridges across the area. Weakening upper energy will then spread into the region on Monday with widespread light snow and flurries expected. The weather remains active as we progress through the work week with several additional systems bringing renewed chances of light rain and snow. && .NEAR TERM /THROUGH TONIGHT/... As of 250 AM EST Sunday...A rather typical early December weather pattern continues today with plenty of cloud cover and lingering chances of northern mountain flurries, at least through early afternoon. Weak high pressure will be building into the area through time, but modest northwesterly flow combined with lingering shallow moisture trapped beneath a persistent synoptic inversion near 850 mb should be a hindrance to more pronounced clearing. Some afternoon sun should be realized in the broader valleys toward mid to late afternoon however as flow trends light. High temperatures close to blended guidance with values in the upper 20s to lower 30s in mountain communities, and lower to mid 30s in the broader valleys. By tonight clouds will thin to partly cloudy in all areas for a brief time as aforementioned surface high quickly traverses through the area. This will be short-lived however as thickening clouds return quickly from the south and west after midnight with approach of a dampening upper level trough and associated vorticity advection/warm thermal advection. Models remain generally consistent with timing of this system with light precipitation overspreading the southwestern half of the forecast area by sunrise on Monday. Thermal profiles plenty cold enough such that p-type will be all of the light snow/flurry variety with a light accumulation of a dusting to perhaps an inch across these areas per blended qpf/GEFS plume output. Low temperatures a bit tricky depending on how much clearing is realized this evening and degree to which thickening clouds put a halt on readings later tonight, but a general idea of 15 to 20 in the mountains and lower to mid 20s in the valleys appears reasonably close at this point. Winds light. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... As of 335 PM EST Saturday...Upper trough will move into the area early Monday morning and exit the area to the east Monday evening. This is not a strong system, but dynamic forcing and low level warm air advection will move across the area. This will provide sufficient lift for light precipitation to move into northern New York after midnight Sunday night and across Vermont during the morning hours on Monday. Thermal profile during this time period supports precipitation to be in the form of light snow with snowfall amounts ranging from a half inch in northeast Vermont to 1 to 2 inches elsewhere. The light snow will begin to taper off Monday afternoon and temperatures in the larger valleys will get into the mid 30s and this may allow for some light rain to mix in. Dynamic support and warm air advection moves east Monday night and precipitation should quickly turn to light snow showers before ending around midnight. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 246 PM EST Saturday...Large scale pattern supports developing mid/upper level trof across the NE CONUS with several systems expected to impact the forecast area. This will support an increasing snow pack across the mountains...with temperatures trending below normal by the end of the week. Models in pretty good agreement with the strongest system with a period of precip impacting our region Thursday into Friday...followed by a period of backside upslope snow and low level cold air advection. Below are some daily thoughts and forecaster perspective. Tuesday...very quiet with building mid/upper level ridge and 1024mb surface high pres directly overhead. Forecast challenge will be if any low level moisture is trapped below developing thermal inversion to produce low clouds...lately this has occurred even when soundings are dry. Will mention partly sunny with progged 850 to 925mb thermal profiles supporting near normal temps for early Dec...mainly upper 20s mountains to near 40f warmer valleys. Wednesday...Both GFS/ECMWF show mid/upper level ridge breaking down...as southern stream short wave energy and a ribbon of enhanced 850 to 500mb moisture moves from southwest to northeast across our region. The energy and moisture seem to be shearing out in the confluent/fast flow aloft across the ne conus...so only anticipating a period of mainly light snow activity. Trends will be monitored for a stronger system with greater moisture advection from the Gulf of Mexico...as current system is now beginning to be sampled better. Models have been consistent showing this system remaining unphased with northern stream energy over the northern plains. Latest guidance shows both 850mb and 925mb temps <0C...supporting all snow...but thinking enough boundary layer warming will occur in the Saint Lawrence and Champlain Valleys to support a mix of rain and snow toward 18z. Dusting to several inches expected in the mountains...will mention likely pops...but thinking impacts will be minimal. Thursday/Friday...This period features the greatest uncertainty as large scale pattern change occurs with modify arctic airmass and a period of precip. Deep mid/upper level trof will be developing across the northern plains with the coldest airmass of the season expected to impact much of the eastern conus. As this trof deepens potent short wave energy and associated arctic boundary will be moving across the central great lakes and eastern conus. GFS/CMC show short wave energy enhancing cyclogenesis over eastern New England...which helps to develop precip along the arctic boundary. This idea would support a widespread accumulating snowfall for most of the area. Meanwhile...latest 12z ECMWF shows an unphased system and no surface low pres developing....supporting a period of rain/snow showers with fropa. Given the expected deep trof amplification...progged potent short wave energy...and magnitude of cold air advection...will trend toward the higher precip solution and mention likely pops. This scenario of a very cold air mass interacting with very warm waters over the western atlantic will be monitored closely...for potential greater impacts. Stay tuned. Temps start near normal for Thursday...but progged 850mb temps btwn -11c and -13c by 12z Friday...support highs only in the teens mountains to upper 20s/lower 30s...with brisk northwest winds. Saturday...Models fall back into better agreement late Friday into Saturday with a favorable period of accumulating upslope snow. Deep mid/upper level trof...along with leftover 850 to 500mb moisture and favorable northwest 850mb winds of 40 to 50 knots...all point to a period of terrain driven upslope snow. Will continue to mention likely pops in the mountains Friday night into Saturday...with temps only in the teens mountains and 20s in the valleys for highs Saturday. && .AVIATION /08Z Sunday THROUGH Thursday/... Through 06Z Sunday...A mix of MVFR and VFR conditions exist as of 00z with mvfr ceilings current at MPV and SLK. There may be a few brief periods of IFR visibilities in snow showers at both SLK and MPV however I didn`t have the confidence to include mention of it in the TAF`s. Persistent northwest flow and plentiful low- mid level moisture will continue to see snow showers in the higher terrain and along the western slopes of the Greens. MVFR ceilings should continue to build in at all terminals except PBG as a low level inversion looks to trap the low level moisture through Sunday morning. At PBG expect the downsloping wind component to help keep ceilings above MVFR thresholds. All sites expected to return to VFR by late morning and by mid afternoon the temp inversion may break down enough to lead to some possible breaks in the cloud cover. Outlook 06Z Sunday through Thursday... 06Z Sunday through 12Z Monday...Trending mainly VFR with high pressure building into the area. 12Z Monday through 12Z Tuesday...Trending BKN/OVC VFR/MVFR cigs with scattered areas of light rain or snow, mainly at KMSS/KSLK. Brief IFR possible at these terminals with this activity. 12Z Tuesday through 06Z Wednesday...VFR/high pressure. 06Z Wednesday onward...trending MVFR/IFR in rain/snow showers. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...JMG NEAR TERM...JMG SHORT TERM...Evenson LONG TERM...Taber AVIATION...Deal/KGM

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