Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 240342 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1042 PM EST Mon Jan 23 2017 .SYNOPSIS... A wintry mix of precipitation will overspread the North Country after midnight tonight and become heavy at times during the Tuesday Morning commute. An extremely hazardous Tuesday Morning commute is anticipated with the icy roads and poor visibilities. A plowable snow and sleet accumulation is likely...along with some ice. Improving weather with above normal temperatures return by Wednesday. && .NEAR TERM /THROUGH TUESDAY NIGHT/... As of 1033 PM EST Monday...Latest trends across e-central NY and s-central VT show sleet as the predominant precipitation type. With slow-moving closed mid-level circulation across the mid- atlantic states, getting plenty of atlantic moisture and above freezing temps aloft moving in on ely 850mb flow of 50-55kts per RAP at 03Z across central New England. The 00Z NAM is in line with observational trends, showing predominantly sleet across much of our region as precipitation develops and intensifies during the pre- dawn hours. It`s rare to get a predominantly "sleet storm", but that appears to be the case given expected thermal profiles, along with pockets of freezing rain during Tuesday morning (especially central/ern VT). Impacts on the morning commute will likely be significant, with moderate to heavy sleet, with pockets of freezing rain expected resulting in icy and hazardous roadways and sidewalks. All in all, no significant changes needed to the forecast attm. Have adjusted onset timing to be a bit quicker, with precipitation (predominantly sleet) underway at SLK/RUT/LEB/VSF and spreading nwd at 0330Z. Anticipate sleet into BTV by 05Z. Heaviest mixed precipitation rates generally 08-14Z most locations. Previous discussion...A complex and extremely difficult forecast with regards to thermal profiles and associated precip types. Complex thermal profiles have started with Whiteface down to 19F and Mansfield at 21F...while BTV is 36F. We have taken a conservative approach in the snow accumulation department...with a general 2 to 6 inches of snow/sleet expected...along with some ice accumulation...especially eastern/central VT...including the Northeast Kingdom. We also have to watch low level cold air bleeding down the CPV on north winds...resulting in more freezing rain. Our thinking is generally between one and two tenths of an inch of ice...with some isolated higher amounts in central/eastern VT. Winter weather advisory continues from 7 PM tonight until 10 PM Tuesday for our entire forecast area. The most intense part of the storm with the highest precip rates will occur right during the Tuesday Morning commute (4 AM to 9 AM)...making for an extremely hazardous morning commute. Water vapor shows well defined closed cyclonic circulation over central NC...with a tremendous feed of deep Atlantic moisture advecting into the NE CONUS/Mid Atlantic. IR sat pic shows a classic mature cyclone with well defined warm conveyor and strong upper level divergence pattern with embedded dry slot over eastern NC. This circulation will slowly move northeast with surface low pres tracking from eastern NC to Cape Cod by 00z Weds. Overall models in excellent agreement with tracking of surface low pres...along with showing deeply negative mid/upper level trof lifting northeast...but weakening through time. This weakening mid/upper level feature...along with limited low level cold air advection will minimize backside bonus snow potential on Tuesday Night. NAM/GFS show band of very strong lift/fgen forcing with strong 700 to 500mb vorticity advection lifting from south to north across our cwa between 2 AM and 10 AM tuesday. Helping to enhance deep layer lift and low level moisture advection will be nose of 45 to 55 knot easterly 850mb jet and anticyclonic curved 250mb jet over eastern Canada. Big question does this strong lift/upper vertical velocities cool the column just enough to support snow or does the low level easterly jet advect warm nose of 4 to 6C air into our region and support a mix of sleet and freezing rain. Still plenty of uncertainty with regards to low level thermal profiles with latest 12z GFS supporting a mostly snow event...while NAM/ECMWF is a mix of sleet/freezing rain...while GEM is in the middle. For example the NAM Bufkit at BTV at 10z shows 5C at 5000 feet associated with southeast wind of 40 knots....while temps at 2000 feet are -6C with low level north/northeast winds draining down the CPV. Meanwhile...same time period GFS shows isothermal layer near 0C from 4500 to 7500 feet with -6C between 1500 and 3500 feet...supporting more snow. Based on complexity of thermal profiles and uncertainty...have gone conservative with snow and utilized a model blend of NAM/BTV4km/GFS/ECWMF to determine precip type and associated snow/ice amounts. This supports a mix of snow/sleet with areas of freezing rain...thinking during the heaviest precip rates mostly snow will occur...with some sleet. As warm layer becomes better established on Tuesday and low level cold air bleeds down the CPV/CT River Valley profiles support more of a freezing rain threat...with more snow/sleet across Northern NY where warm nose is limited. However...boundary layer temps are just marginally cold enough...so ice accumulation is uncertain at this time...especially CPV where temps today are in the mid/upper 30s. Given downslope easterly flow...would not be surprised if temps warm into the mid/upper 30s from Mt Holly to East Middlebury to Underhill to support some rain on Tuesday Afternoon. Expecting a break in the heavier precip by mid-morning into early afternoon...before next round of light to moderate mix rain/sleet and freezing rain develops on late Tues Afternoon/Evening...as closed system lifts northeast. Timing of this secondary surge of precip could impact the evening commute with another round of light wintry mix slowly changing back to snow showers from west to east toward midnight...as profiles cool. Bottom line for snow/sleet accumulation is generally 2 to 6 inches with some higher amounts possible Dacks/SLV and parts of the southeast upslope region of the Green Mountains. Ice accumulations of a trace to 0.10 of an inch CPV...with 1 to 2 tenths of an inch possible across central/eastern VT...including the Northeast Kingdom. The heavy wet snow/low ratios and freezing rain will probably lead to some power outages. Overall storm total qpf will range between 0.50 and 1.0 with highest values along the se upslope regions of the Green Mountains from Ludlow to Mansfield and another stripe along the eastern Dacks. Expect some shadowing along the western slopes from near Rutland/Danby to North Underhill and over the Northeast Kingdom. Given winds expect terrain to impact qpf amounts for this system. Qpf ranges from 0.25 to 0.75 across the western dacks/slv...as moisture depth is less. Wind threat is minimal and relatively small area along the western slopes from Danby/Rutland to East Middlebury...with isolated gusts to 30/35 mph possible. Mixing is limited as strongest winds occur when precip rates are the strongest. Temps cool into the mid/upper 20s to lower 30s tonight and warm upper 20s to mid 30s...warmest along the western slopes. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... As of 332 PM EST Monday...By Wednesday morning aforementioned low pressure will be over the Gulf of Maine and Nova Scotia, with deep layer moisture rapidly shifting northeast of the BTV CWA through the day. Could see some lingering snow showers across the high peaks in the morning, but by mid-day weak mid/upper level ridging briefly builds in so expect to see some afternoon sun, especially across central and southern areas. Highs will continue to run well above normal in the 30s. Break in active weather is very short as another deep mid/upper level trough over the central CONUS begins to shift eastward Wednesday night, with surface low pressure over the Great Lakes Wednesday shifting northeast in the Ottawa/St. Lawrence Valley. Favorable southwesterly flow combined with increasing low/mid level moisture will enhance precipitation potential downwind of Lake Ontario and points northeastward into northern New York, the northern Champlain Valley and north-central Vermont through the night with boundary layer temps supporting mainly snow except a rain/snow mix across southern portions of St. Lawrence county. As the boundary layer warms further Thursday, precipitation becomes more mixed area-wide until the low pulls east of the area Thursday afternoon and cold air advection develops on increasingly northwest flow. Overall not looking for a lot of QPF through the period, so snow amounts will generally be a dusting to perhaps 2 inches, and locally up to 2-4" across the high peaks. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 332 PM EST Monday...Long term period for Thursday night through the weekend highlights a broad upper trough across the majority of the CONUS with no big systems on the horizon, rather daily chances for light precipitation especially across the high peaks. Temperatures return to more seasonal values though still slightly above normal with highs mainly in the 20s and lows in the teens which supports mainly snow as the dominant ptype for anything that does fall. Best chances look to be Thursday night through Sunday as we remain under cyclonic northwesterly flow with light snow accumulating along the higher peaks, followed by drier conditions for Sunday into Monday. && .AVIATION /04Z Tuesday THROUGH Saturday/... Through 00z Wednesday..VFR overall to start the period with KRUT being the exception with MVFR ceilings. Conditions will deteriorate rapidly to a mix of low MVFR/IFR as wintry precip moves in overnight after 07Z. The forecast trend continues to show the precip moving in late overnight between 03-06z in southern Vermont and between 09-12z across central and northern Vermont and across Northern New York. Expect a variety of precip types with a mix of rain/snow/sleet and freezing rain possible. Additionally with the icing layers just off the surface conditions could be dicey with icing in the low levels of the atmosphere. An easterly low level jet is expected to create gusty winds at RUT and also cause issues with low level turbulence and wind shear due to the speed differences from the ground to 2500-3000 feet agl. Winds overall will also be northeasterly at 05-10 knots for most of the period. Outlook 00z Wednesday through Saturday... 00z Wednesday - 12z Wednesday: MVFR/IFR trending towards VFR/MVFR as the wintry precip tapers off Tuesday evening. 12z Wednesday - 12z Thursday: VFR with skies becoming cloudy late. 12z Thursday onwards: Generally VFR with on and off chances of MVFR in periods of rain and snow showers. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Weather Advisory until 10 PM EST Tuesday for VTZ001>012- 016>019. NY...Winter Weather Advisory until 10 PM EST Tuesday for NYZ026>031- 034-035-087. && $$ SYNOPSIS...Taber NEAR TERM...Banacos/Taber SHORT TERM...Lahiff LONG TERM...Lahiff AVIATION...Deal/MV

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