Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 110547

Area Forecast Discussion
National Weather Service Burlington VT
1247 AM EST Sun Dec 11 2016

A cloudy and chilly evening is expected as high pressure crests
over the North Country. The coldest air of the season will see
lows overnight dropping into the single digits for most of the
eastern Vermont and Adirondacks with teens expected for the
Champlain and Saint Lawrence Valleys. The Monday morning commute
is expected to be significantly impacted as our next system
arrives on Sunday Night into Monday with a widespread
accumulating snowfall expected. Total snow accumulations will
range from 3 to 7 inches by Monday afternoon.


As of 1248 AM EST Sunday...Southerly flow channeling up the
Champlain valley with some stubborn clouds remaining over
portions of Northern VT. Cloud cover affecting radiational
cooling, leading to varying temperatures into the morning hours.
Areas of clearing in the Adirondacks and Northeast Kingdom show
temperatures in the negative single digits, meanwhile BTV under
persistent clouds is currently in the upper teens. Overall
forecast in good shape.

Through Sunday afternoon expect partly cloudy skies to increase
and thicken as a low pressure system begins to lift north.
Latest runs of the hires guidance show the warm air advection
precip moving in even faster than the previous couple of days
and so by 21z expect light snow showers to already be falling
over the Saint Lawrence valley. The precip should quickly
overspread the rest of the North Country due to a strong low
level jet developing Monday evening.


As of 245 PM EST Saturday...An active period of weather still
on track to affect the region Sunday night into Monday with
widespread accumulating snows. Latest model data continues to
support the idea that Great Lakes low pressure will track east
and drive an occluding warm front across our area during this
time frame with modestly robust isentropic lift and moisture
advection being the primary driver for precipitation. Current
thinking maintains consistency with prior forecasts offering a
widespread 3-7 inch snowfall by late morning/early afternoon on
Monday, and given this consensus have issued Winter Weather
Advisories for the area Sunday evening into the first half of
Monday accordingly. Slight snowfall variation due to
shadowing/upslope effects will also be possible given mean
925-850 mb flow will hover from 150-170 degrees at 30-50 kts
during the core of the event. Thus local enhancement along the
eastern faces of the southern Green Mountains looks plausible
with slightly lesser totals along leeward/western facing
mountain slopes. However, given depth of moisture and dynamical
forcing feel overall uniformity in snowfall distribution will be
on the higher side. By Monday afternoon consensus remains high
that as the primary low tracks north of our area we`ll enter a
pronounced dry slot with precipitation trending more scattered
and lighter over time. With mid to upper levels trending
unsaturated some patchy light rain, drizzle or even freezing
drizzle will be possible across portions of the area as
temperatures climb near or slightly above the 32F mark. Any
light freezing drizzle that would occur seems most likely across
our southern VT counties east of the Greens. However, given the
lighter character of the afternoon precipitation any icing
threat should be minimal. In terms of temperatures I did base
max/min values off 3- hourly hi-res/bias-corrected data showing
readings trending steady or slowly climbing Sunday night,
topping out in the 30s on Monday.

By Monday night parent cold front sweeps through the area with
background flow trending westerly over time and lingering snow
shower activity becoming more confined to the northern mountains as
orographically processes begin to dominate. Lows holding fairly
mild however - generally 20s to locally around 30 in the
Champlain Valley.


As of 245 PM EST Saturday...Subtle changes exist in this
morning`s global models for the middle to later portions of next
week, though by and large the overall idea of a trend toward
much colder weather with scattered flurries/snow showers still
appears reasonable at this point. Main player will be a large-
scale cyclonic polar gyre that will drop across southern Canada
during late week and force a pronounced arctic boundary through
the area on Thursday. Enhanced snow shower activity likely to
get going in the Lake Ontario snowbelts on Wednesday as
west/southwest flow continues in earnest ahead of the boundary,
with activity sweeping through Vermont by Wednesday night along
the front. Some minor accumulations certainly possible here,
with slightly heavier totals in the snowbelts. Behind this
boundary the coldest airmass of the season will arrive with some
preliminary data suggesting at least the possibility of lower
wind chills on Thursday night. Highs start the period mild (30s)
on Tuesday, cooling into the 20s by Wednesday, 10 to 20 on
Thursday and upper single digits to teens on Friday. Lows follow
suit with the coldest readings occurring Thursday night and
Friday night when readings fall into the positive/negative
single digits.

By next weekend, broad consensus continues showing our next system
of midwestern origin will take a Great Lakes/St. Lawrence Valley
storm track with a renewed threat of more widespread precipitation
and temperatures moderating back toward more typical mid-
December values.


.AVIATION /06Z Sunday THROUGH Thursday/...
Through 06z Monday...VFR conditions will largely prevail through
the majority of Sunday with variable Claudine`s expected
through 21z. After 21z, clouds increase markedly from the
southwest to northeast ahead of our next system which will
spread light snow over the region after 00z. Cigs/vsby will
lower to MVFR/IFR by the end of the 24 hour period with winds
generally out of the southeast at 5-10kts.

Outlook 06z Monday through Thursday...

00z Monday - 00z Tuesday: MVFR and IFR in light snow. LLWS and
turbulence possible.

00z Tuesday - 00z Thursday: Mix of VFR/MVFR in scattered snow
showers, with brief IFR possible.

00z Thursday - 00z Friday: MVFR/IFR snow showers likely along
an arctic frontal passage.


VT...Winter Weather Advisory from 7 PM this evening to 1 PM EST
     Monday for VTZ001>012-016>019.
NY...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST
     Monday for NYZ026>031-034-035-087.


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