Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 072344

Area Forecast Discussion
National Weather Service Burlington VT
644 PM EST Wed Dec 7 2016

An unsettled pattern is expected across the North Country through
the end of the week...with occasional snow showers and isolated snow temperatures drop to below normal levels by the
weekend. Total snow accumulations of 3 to 6 inches with isolated
higher amounts will be possible south of Route 3 in Saint Lawrence
County and the northern mountains of Vermont and New York. A dusting
to several inches possible in the valleys with periods of hazardous
travel possible.


As of 629 PM EST Wednesday......Lake snow advisory continues for Southern
Saint Lawrence County mainly south of Route 3 for 4 to 8 inches
of snow by Thursday Night...

Not much to add for the evening update. Some small adjustment to
temps in the St Lawernce Valley as the saw a brief period of
clearing before sunset that gave them a little extra heating
and warmer than expected temps. Timing still looks good for snow
to begin in the St Lawrence Valley after 08z.

Previous Discussion...Forecast challenge will be timing of snow
showers and squalls across our region...along with potential
impacts and accumulation. Large picture shows closed 5h/7h
circulation over the northern Great Lakes with broad southwest
flow aloft across the northeast conus. Watching increasing mid
level moisture and weak elongated vort over the central/northern
plains moving our way for Thursday. This energy and moisture
aloft...will combined with cooling thermal profiles to produce
occasional snow showers and isolated snow squalls across parts
of our region. High resolution models show ingredients coming
together with instability...moisture...and favorable southwest
aligned flow around 12z Thursday across central Saint Lawrence
County. Latest 4km NAM and locally developed BTV 4km shows this
band intensifying btwn 15z-21z low level
instability increases from surface heating and cooling aloft
associated with trof and deeper moisture feed from Lake Ontario.
Very difficult to determine organization of band without a
sharp convergence line and limited deep layer moisture...but
thinking snowfall rates of up to 1 inch per hour are possible.
Qpf/snowfall is the greatest from southern Saint Lawrence Valley
into the northern mountains of vt near Jay Peak where snow
accumulations of 2 to 6 inches are likely with isolated higher
amounts. Elsewhere...away from the most persistent lake effect
snow shower activity...a dusting to several inches is possible.

Have noted high resolution data shows intense omega couplet...along
with favorable moisture in snow growth area at BTV around 18z
Thursday...along with a quick 0.05 to 0.10 of qpf...which could
produce a burst of 1 to 2 inches of snow right before evening
commute. This band is progged to shift south and dissipate across
central/southern vt by 21z Thursday. Temps mainly in the mid/upper
20s to mid 30s...but falling back into the teens and 20s on Thursday
Night. Forecasting these events are difficult with timing and
intensity...but something we will watch very closely over the
next 12 to 18 hours.

Thursday Night...mid/upper level trof deepens with leftover 850 to
500mb moisture in the trof axis. This combined with developing
upslope flow and moderate low level cold air advection will produce
a period of favorable upslope snow from 03z to 12z Friday. Soundings
show good moisture in snow growth region...along with enhance 1000
to 700mb omega across the northern dacks into the central/northern
green mountains from near Sugarbush to Stowe to Jay Peak. Have
increased pops to likely/cat...including the eastern
cpv...associated with some lake champlain moisture enhancement.
Expecting a high fluff factor with additional snow accumulations of
2 to 6 inches in the mountains and another inch or so across the
eastern champlain valley. Temps drop to near normal for lows ranging
from the teens to mid 20s.


As of 300 PM EST Wednesday...Work week ends with surface low pressure
continuing to pull northeast through the Canadian maritimes
while cyclonic mid/upper flow persists across the North Country.
Higher elevation upslope snow showers persist through much of
Friday on west/northwest flow, with a few more inches of snow
possible generally above 1000 feet, but activity will begin to
dissipate going into Friday night as surface high pressure
builds into the Ohio Valley. Temperatures will be slightly below
seasonal normals with highs in the mid/upper 20s to lows mainly
in the teens.


As of 300 PM EST Wednesday...For Saturday and Saturday night
aforementioned high pressure builds into the northeast with dry
conditions expected. Aloft the mid/upper flow remains out of the
west/northwest so despite strong subsidence at the surface,
feel we`ll see a good deal of clouds around. Strong cold air
advection on the front-side of the high will continue to provide
below normal temperatures with highs only in the teens to 20s,
and widespread single digits to low teens for lows Saturday

For Sunday onward, large uncertainty continues to exist with the
forecast with increased model differences from the 00z suite in the
handling/phasing of energy pulling out of the lee of the Rockies
Saturday night. Latest ECMWF and CMC continue to offer a deeper
trough with the ECMWF phasing with the northern stream pulling a
robust surface low northeast through the Ohio Valley Sunday night
and the St. Lawrence and Ottawa Valleys through Monday night. The
CMC however does not phase, keeping the surface low more suppressed
to the south, and the GFS while it does phase with the northern
stream offers a much weaker trough and surface low with little
impacts. Your guess is as good as mine as to what happens here, so
for now I`ve offered a blended model approach with mid-chances for
some light snow.

Models do come into better consistency though heading into the
middle of next week behind whatever system we get for
Monday/Tuesday. The trend here will be towards much colder air with
possibly our first arctic outbreak as a deep cold low settles over
southern Ontario/Quebec and strong surface high pressure develops
over the central CONUS. Coldest air looks to arrive beyond this
forecast period though, so stay tuned.


.AVIATION /00Z Thursday THROUGH Monday/...
Through 00Z Friday...Overall VFR conditions across the region
with KSLK still lingering with MVFR ceilings. Expecting VFR for
most locations with short periods of potential MVFR/IFR with
brief passing snow showers tomorrow. KSLK should see the worst
with possible IFR/LIFR conditions possible on Thursday. Light
southerly winds at 05-10 knots overnight should give way to a
southwesterly direction tomorrow with the St Lawrence Valley
also seeing a gustier 10-20 knots in the afternoon.

Outlook 00Z Friday through Monday...Occasional snow showers
with a brief snow squall possible btwn 00z-06z Friday...with
rapid change in vis/cigs likely in any snow squall. After 00z
snow showers become confined mainly to the mountains with ifr
conditions lingering at mpv/slk through 12z Friday. Mvfr cigs
linger at slk/mpv on Friday with vfr developing Friday night
into Sunday. Next system arrives on Sunday afternoon with
another widespread light snow event. This system will produce
widespread ifr conditions between 18z Sunday into 12z Monday.


NY...Lake Effect Snow Advisory from midnight tonight to midnight
     EST Thursday night for NYZ029.


LONG TERM...Lahiff
AVIATION...Taber/MV is the U.S. government's official web portal to all federal, state and local government web resources and services.