Area Forecast Discussion
Issued by NWS Burlington, VT

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356 FXUS61 KBTV 230220 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1020 PM EDT Sat Oct 22 2016 .SYNOPSIS... Deepening low pressure along the Maine coast will track northward into southern Quebec by Sunday morning, before slowly shifting to the east. Wraparound precipitation will continue through tonight, with higher elevation rain changing to snow before tapering off to snow showers during Sunday morning. Several inches of snow accumulation are possible across the Adirondacks, and also in Vermont, generally above 1500 to 2000 feet, overnight tonight. Variably cloudy and seasonably cool conditions will prevail Monday through Wednesday. Another wave of low pressure approaching from the Great Lakes and Ohio Valley will bring the next chance for rain, generally later Thursday into Friday. && .NEAR TERM /THROUGH SUNDAY NIGHT/...
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As of 1020 PM EDT Saturday...Mid-level winds have started to back from northeast to north-northwest on CXX VWP over the past couple hours. As such, it appears that colder northwest flow has now advanced as far east as western Vermont with mid-level low centered over east-central Vermont. Have heard of spotter reports this evening of rain mixing in with wet snow across northern and eastern Franklin County VT with temps in the mid 30s. I did lower temps slightly in eastern Chittenden and Franklin Counties in Vermont, which in turn introduces more of a rain/snow mix for these areas a bit earlier through the rest of the overnight. Cold advection will continue to progressively advance to the northeast resulting in snow levels falling to around 800-1000` as the overnight progresses. The forecast thinking still remains the same across Vermont: that being that the most significant accumulations of wet snow will be limited spatially to the spine of the Greens and at elevations above 1500`, snow amounts should be limited to a coating on mainly grassy surfaces across a good portion of central and eastern Vermont. The Winter Weather Advisory continues in the Northern Adirondacks, and I`ve also gone ahead and refreshed some of the wording with this forecast update. Wet snow has started to accumulate now on pavement in these areas, with spotters indicating accumulations from 1-2" in locations such as Lake Placid. Still think an additional 2-4" of snow is in order for these areas until it tapers to snow showers into the mid-morning hrs Sunday. As is the case for Vermont, snowfall accumulations will exhibit a strong elevation dependency. As pressure gradient continues to increase, west winds will stand to increase and become gusty as well across the entire forecast area. In the higher elevations, gusts up to 40 mph in conjunction with accumulations of dense snow overnight may pose a risk for scattered power outages. Previous near-term discussion issued at 252 PM follows... Main concerns this forecast period are snow levels tonight, and gusty winds to 40 mph late tonight through Sunday as strong low pressure tracks to our east across Maine into ern Quebec. Winter Wx Advisory continues nrn Adirondacks thru 15Z Sunday. 985mb surface cyclone along the mid-coast region of Maine will continue to track nwd while deepening, reaching the St. Lawrence Seaway by sunrise Sunday. Deep mid-upr level trough has acquired negative tilt, extending from southeastern Ontario across w-central NY into PA/NJ. As the upper trough pivots newd this evening, will continue to see dynamic cooling and advection of colder 925-850mb temps from SW-NE into nrn NY, and eventually across VT. 850mb temps near 0C at 19Z across the nrn Adirondacks will cool to near -3C to -4C by 06Z tonight, allowing snow levels to continue to fall from near 1500-2000` to below 1000` later tonight. Cooling thermal profiles already yielding changeover to snow at Tupper Lake (per NY Mesonet) and SLK ASOS, with 19Z temp at 33F. Strong upper divergence in left front quad of upper jet and deformation axis will continue to produce precipitation across nrn NY through the overnight hrs. Also, WNW to NW low-level flow will increase, producing more of an orographic character to the snowfall across NRN NY late this evening, and across VT after midnight. Have continued winter weather advisory for nrn Adirondacks, for 3-5" of snowfall, highest at elevations near 2000` and higher. Across higher elevations of VT, also anticipate a change to snow as colder thermal profiles develop after 00Z. May even see some wet snowflakes in the Champlain Valley after 06Z and through daybreak. Temps won`t support accumulation in the Champlain Valley (lows 36-39F), but could see a coating to an inch across most cities and towns central/ern VT, and then upwards of 6-8" for the highest summits, especially Jay Peak to Mt. Mansfield, before activity ends mid-day Sunday across far nrn VT. Main impact will be some slippery wintry travel due to wet/slushy accumulation on roadways after sunset, especially across the higher passes of NY/VT. With strong elevational dependence to the snowfall, travelers may also see large variations in road conditions over short distances, so that will be something to watch for. Strong gradient flow on backside of departing low pressure will yield increasingly windy conditions late tonight and through the daylight hrs Sunday. Sustained winds of 15-25 mph, with gusts locally to 35-40mph are expected. Higher elevation areas with wet snow accumulation may see some isold power outages owing to snowfall and developing moderately strong winds. May see some partial clearing very late Sunday, but overall windy and raw conditions with lower elevation high temps generally in the 40s (near 50F at BTV). Gradient flow diminishings Sunday evening, with quieter weather conditions for Sunday night. Lows Sunday night generally 35-40F, but locally near freezing in the nrn Adirondacks.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... As of 323 PM EDT Saturday...This weekends cut-off will have moved into Quebec by Monday with a broad trof still influencing the weather across the North Country through this period. This will bring climo...upslope favored rain/snow showers across higher terrain late Monday into longer term period. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 323 PM EDT Saturday...As mentioned in short term...broad trough maintains influence across region through late Tuesday. This will bring climo...upslope favored rain/snow showers across higher terrain through Tuesday and then tapering off by Wednesday. Sharp shortwave ridge due to departing first trof and next upstream shortwave will bring surface high for Wed-Wed Ngt then depart on Thu with the approach of upstream shortwave. Models have backed off timing of precipitation until late Thu which I initially had delayed thus in agreement moving in Thu afternoon and continuing most of Fri. On Sat...differences between ECMWF and GFS will GFS more robust with another surface system where ECMWF weaker but enough of cyclonic flow that a threat of showers in northern mountains looks reasonable this far out. Highs in the 40s through Thursday and back to seasonable L50s by Friday and Saturday. && .AVIATION /02Z Sunday THROUGH Thursday/... Through 00z Monday...Widespread VFR/MVFR ceilings and visibilities expected through about 15z before improving to VFR for the remainder of the period. However...there will be periods of IFR conditions due to rain and snow moving across the area through about 10z before sharply decreasing in areal coverage or being confined to the higher terrain. The majority of any snow will be confined to elevations above 1000 feet. Gusty west to northwest winds will prevail through much of the period...however after 15z the winds will be strongest with gusts in the 20 to 30 knot range. Outlook 00z Monday through Thursday... 00z Monday through 00z Wednesday: A mix of VFR/MVFR with upslope showers in NW flow. 00Z Wednesday through 00Z Friday: IFR/MVFR fog development possible during the early morning hours. && .HYDROLOGY... As of 320 PM EDT Saturday...Additional rainfall up to an inch or so is expected. Dry antecedent conditions and absence of extreme rainfall rates should continue to preclude any river/stream flooding. Only some minor urban and street flooding is possible associated with falling leaves clogging storm drains, etc. widespread flooding is anticipated. && .MARINE... AS OF 706 PM EDT Saturday...West to northwest winds have increased to 15 to 25 knots on Lake Champlain early this evening. These winds will continue to stay at least in this range owing to sharp west to northwest pressure gradient associated with deepening low located over central Maine. Based on current indications from the 18z BTV-4km WRF, it is likely that lake winds will stay above Lake Wind Advisory criteria into a good part of Sunday as well. Waves will build into the 2 to 3 foot range. These tend the highest on east-facing shores exposed to a greater fetch on west winds; specifically those locations adjacent to the open waters north of the Charlotte Ferry and south of Valcour Island. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...Winter Weather Advisory until 11 AM EDT Sunday for NYZ029>031- 034. && $$ SYNOPSIS...Banacos NEAR TERM...Banacos/Loconto SHORT TERM...SLW LONG TERM...SLW AVIATION...Evenson/SLW HYDROLOGY...KGM MARINE...Loconto is the U.S. government's official web portal to all federal, state and local government web resources and services.