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Area forecast discussion
National Weather Service Burlington Vermont
931 am EST sun Dec 15 2019

gusty westerly winds are expected today across the north country,
along with scattered mountain snow showers. A few inches of
additional snowfall can be expected, as temperatures slowly drop
back into the 20s and 30s. Winds generally 20 to 35 mph with
localized gusts up to 50 mph possible, which may cause a few
isolated power outages. Quieter weather returns for Monday, before
light snow returns for Tuesday and potential snow squalls on
Wednesday of this upcoming week. Temperatures will be near
seasonable levels to start the work week.


Near term /through Monday/...
as of 931 am EST Sunday...overall forecast in good shape with
respect to advisories and will continue at this time. Have
tweaked precipitation chances for today, mainly across the
Champlain Valley and west slopes of the Green Mountains, where
radar shows greater areal coverage of the showers. These showers
should continue through the morning hours before becoming more
terrain driven this afternoon. Based on temperature trends have
slowed the cooling down for today just a bit. Otherwise Wind
Advisory on track along with additional snow accumulations for
the higher terrain today.

Previous discussion...
have updated fcst with several changes based on current and
expected conditions. First was to expand likely pops and
increase qpf/snowfall across the southern Green Mountains near
Killington. The combination of strongly aligned westerly flow
and colder air moving over Lake Ontario, expecting lake effect
snow showers to travel downwind of the lake today. In addition,
as this moisture is lifted along The Spine of The Greens, some
localized enhanced precip/snowfall is possible. Latest snow
grids have up to 4 inches across eastern Rutland.

Next change was to increase timing of stronger wind gusts as
gusty winds have developed a little faster than originally
anticipated. Already have seen gust to 54 mph at Mendon, 53 mph
at Ellenburg and 51 mph at Johnson. Otherwise, Wind Advisory
looks good with localized gusts in the favorable eastern
downslope regions up to 50 mph.

Winter wx advisory continues for dacks as upslope flow continues
with additional snow showers persisting. Additional snowfall of
1 to 2 inches possible, combined with gusty winds will create
areas of blowing and drifting snow, especially as snow becomes
lighter with colder profiles.

Previous discussion:
Winter Weather Advisory continues for storm total snowfall of 3
to 5 inches of snow for the northern Adirondacks in New York
until 18z.

Wind Advisory in effect through 00z Monday for eastern Adirondacks
and portions of central, eastern, and northern Vermont, including
the nek for localized gusts up to 50 mph and potential isolated
power outages.

Sfc analysis shows powerful 974mb low pres quickly lifting toward
eastern Canada, while brisk westerly winds prevail across our fa.
Back edge of deformation precip is lifting acrs northern NY, with a
transition to upslope/trrn focused snow showers will evolve this
morning. Little change in storm total snowfall anticipated with 3 to
5 inches northern dacks and 2 to 4 inches northern greens through
18z today.

Winds will be gusty from the west today, especially as deeper mixing
develops under moderate llvl caa. Soundings show top of the mixed
layer winds of 45 to 55 knots, while bottom values of 35 to 40
knots, which with perpendicular cross barrier/mtn flow will result
in localized gusts to 50 mph today. The strongest winds will occur
in the favorable downslope regions of the eastern dacks and on the
east side of the green mtns and Worcester range in Vermont. The core of
strongest 850 to 925mb winds occurs btwn 09z this morning and 18z
today, but best mixing is from 15z-21z, which will represent the
best time period for localized gusts to 50 mph. A few isolated power
outages are possible, along with some small shallow rooted trees,
especially given saturated soils.

Moderate caa continues as 925mb temps range btwn -4c to 0c at 12z
this morning, but quickly drop btwn -7c to -11c by 00z this evening,
as a result of gusty westerly winds. Have the general idea of
falling temps in the grids, with values starting in the 30s to near
40f, but dropping into the teens and upper 20s by evening. Any
lingering snow will dissipate by tonight, as moisture profiles
decrease and weak sfc high pres builds into our fa. Expect partly
cloudy skies with temps dropping back single digits to near 20f,
warmest values near Lake Champlain. Monday is relatively quiet with
slightly below normal temps and much lighter winds.


Short term /Monday night through Tuesday/...
as of 332 am EST Sunday...for Monday night, increasing clouds with
lows in the lower 20s to mid teens. Heading into Tuesday, forecast
guidance has trended slower and further south with regards to the
surface low track. Where models disagree this evening is how far the
precipitation shield extends north. One thing our region will be
combating is low- level dry air. At the time of the best saturation
in the dendritic growth zone towards Tuesday morning, there will be
low-level dry air in place with subsidence as well. Anticipate virga
to begin the day on Tuesday. Once the lower levels become adequately
saturated late morning/early afternoon, we should begin to see snow
fall across most areas, though the St. Lawrence Valley will be the
most likely to miss out.

Seeing several mixed signals with regards to the snow ratios. The
Cobb technique indicates values close to 15:1, and the depth of the
dendritic growth zone is nearly 5000ft. However, the aforementioned
dry air initially will result in some sublimation, and by the time
everything becomes well saturated, the better vertical motion starts
to exit the region.

The latest forecast amounts still looks good for 2"-4" across south-
central Vermont with pockets of 5" possible and then 2" or less,
especially as you head northwest towards the St. Lawrence Valley.
Highs will top out in the mid 20s to near 30.


Long term /Tuesday night through Saturday/...
as of 332 am EST Sunday...Wednesday will begin as a rather benign
day, but that will quickly change as a strong upper low that is
nearly pushing sub 500hpa heights advects into the region. A clipper
low will deepen as it moves southeastward towards btv and draws
moisture from Lake Ontario ahead of it. Forcing should be vigorous
ahead of the strong baroclinic zone from the strong cold air behind
it. Forecast soundings are certainly impressive. It will not be long
before this event falls within the scope of higher resolution
models, and it will be closely monitored, as snow squall potential
already looks quite high.

Behind the system, very cold temperatures with lows in the single
digits above and below zero and highs struggling to get into the
teens for a couple days. We will moderate over the weekend with very
dry conditions behind the polar front.


Aviation /15z Sunday through Thursday/...
through 12z Monday...strong and gusty westerly winds will
continue today at 20 to 30 knots and localized gusts up to 35 to
40 knots likely. Areas of moderate turbulence likely given
cross runway flow at btv and winds perpendicular to the trrn
across all our taf sites.IFR conditions from the combination of
low cigs and occasional snow showers with vis btwn 1-2sm will
prevail at slk most of the day. Scattered snow showers may
impact the rut terminal as lake moisture is advected downwind of
Lake Ontario on gusty westerly winds. Brief periods of MVFR/IFR
vis with mainly MVFR cigs prevailing at rut. Elsewhere, VFR
conditions with occasional MVFR cigs at btv/mpv/mss and pbg.
Winds decrease by sunset with all sites trending toward VFR


Monday: VFR. No sig weather.
Monday night: VFR. No sig weather.
Tuesday: mainly VFR, with areas MVFR possible. Chance snow.
Tuesday night: mainly MVFR, with local VFR possible. Chance shsn.
Wednesday: mainly VFR, with areas MVFR possible. Chance shsn.
Wednesday night: mainly VFR, with local MVFR possible. Slight
chance shsn.
Thursday: VFR. No sig weather.


Lake Wind Advisory has been issued for west winds of 15 to 25
knots with localized gusts up to 30 knots possible. Winds should
weaken this afternoon as powerful low pressure shifts away from
the region. Wave generally in the 1 to 3 foot range, given the
short fetch associated with the westerly wind component.


Btv watches/warnings/advisories...
Vermont...Wind Advisory until 7 PM EST this evening for vtz003-004-
New York...Wind Advisory until 7 PM EST this evening for nyz031-034.
Winter Weather Advisory until 1 PM EST this afternoon for



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