Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1241 am EST Wednesday Dec 11 2013
snow showers and perhaps a heavier snow squall are expected
Wednesday ahead of a strong Arctic cold front. Highs on Thursday
will only be in the teens area wide and not much warmer Friday.
Perhaps a few snow showers each day. A storm system will probably
affect the region late Saturday into Sunday, bringing the
possibility of a widespread snow.
Near term /until 6 am this morning/...
as of 1216 am EST Wednesday...only minor adjustments to cloud
cover with latest update. Currently less clouds than advertised in
some areas...but they are expected to fill in once again towards
morning. No other changes at this time.
forecast remains on track as we head into the late evening and
overnight hours. Did opt to trend min temperatures up by 1-3 degrees
based off latest lamp guidance and owing to the fact that we'll
likely maintain at least some light to modest winds/mixing in the
planetary boundary layer overnight. Areal coverage of flurries/shsn remains unchanged
with spotty coverage across the higher terrain of central/eastern
Vermont...and slightly better coverage across the western/southwestern
dacks in closer proximity to intensifying Lake Ontario snow band.
Accumulations fairly negligible in Vermont...though perhaps an inch or
two possible in the dacks from Minerva/olmsteadville to Newcomb at
the eastern terminus of the snow band. Have a great night.
Short term /6 am this morning through Thursday night/...
as of 350 PM EST Tuesday...as we start Wednesday, we should
continue to see the lake effect band shift a bit more, spreading
some snow showers into southeast St Lawrence County and southern
Franklin County in northern New York. Could be a few inches of
accumulations in isolated spots. Later shifts will need to check
out the need for any lake effect snow advisories.
Otherwise the main weather maker will be an approaching cold front
that is associated with the upper trough. Elements still look to
be in place for a 6 hour window where that front could generate
localized snow squalls. Have a little bit of instability and with
the southwest winds ahead of the front, that will provide both
some frontal convergence and be able to tap moisture from the Lake
Ontario snow band. Main period is about 20z when the front and it's
associated snow showers and squalls will be up along the New York/Canada
border to about 03z when it reaches a line from northeast Vermont to
the southern Champlain Valley.
The snow squalls could dump 1/2" or so in less than 30 minutes,
and lead to some slick Road conditions. A brisk southwest wind,
gusting 25 to 30 miles per hour will also blow that snow around, causing even
more reduced visibilities.
That front will also usher in some cold air. 850mb temperatures
ahead of the front will be around -18c (already chilly to begin
with) and fall to -20 to -24c after. How cold it gets Wednesday
night will depend on whether we clear out. Still maintain some
cloudiness, but still cold enough to go sub-zero in the colder
areas and just single digits in the "warmer" valleys.
Thursday will be cold. Teens will be it for the highs. Decent
amount of low level moisture around, so don't be surprised for a
Long term /Friday through Tuesday/...
as of 350 PM EST Tuesday...pretty much relied on the superblend
(blend of all available guidance) as it is usually the best way to
go, and again in this case it seems like quite a reasonable forecast.
Friday...still below normal temperatures with 850mb heights about
-13 to -16c. High temperatures will struggle to the lower 20s for
the low elevations. Teens elsewhere. At least that is warmer than
it will be Thursday! Weak trough embedded within a broad westerly
flow should pick up moisture from the Great Lakes and give US
quite a bit of clouds and a few flurries or light snow showers.
Have painted in quite a bit of 25-35% probability of precipitation.
Saturday and Sunday...this continues to be the primary Point of
interest for the long range as there remains a storm threat. Decent
amount of consistency (though far from identical solutions)
between 12z Euro and 12z GFS. So confidence is moderate we will
see some effects. Too far out to pinpoint any details. Models both
show a primary low with the upper trough over the Great Lakes,
while energy gets transferred to a secondary coastal low beginning
late Saturday. GFS is a bit stronger with the primary low than the
Euro. Either way, this type of scenario is typically not one for
any huge dumps of snow. Rather we usually end up with decent snows
on the leading edge warm air advection, and then get dry slotted
and lose the moisture and lift, leading to only light precipitation
for the 2nd half of a storm. Initial gut feeling is for a
widespread advisory level snow event, but again too far to really
pinpoint anything. Best advice -- continue to follow later
forecasts! With the increasing confidence in some storm, have
increased probability of precipitation into the likely category for Saturday night and
into Sunday. Precipitation will come to an end Sunday night.
Monday...additional shot of chilly air comes in the wake of the
departing storm. 850mb temperatures drop to -16 to -19c (brrr).
Another day with highs in the teens area wide. Some residual
moisture, mainly higher terrain of the Northeast Kingdom, so
perhaps a few flurries there, otherwise dry.
Tuesday...high pressure starts the day. Will probably be a cold
start given relatively new snow cover, with sub-zero readings
nearly everywhere outside of the Champlain Valley. Brrr. Otherwise
fast flow aloft will start to bring the harbingers of another
system (much weaker), so have some increasing clouds and low
chances for snow showers.
Aviation /06z Wednesday through Sunday/...
through 06z Thursday...generally VFR conditions are expected
through the period though chances for MVFR/IFR snow squalls exist
this afternoon as an Arctic boundary sags southward through the
area. Too early to time such a mesoscale feature hitting a terminal
so will just include some vcsh for now... winds
overnight turn southwesterly after 12z...then back to west/northwest
behind the boundary and could be gusty at times.
Outlook 06z Thursday through Sunday...
06z Thursday through 12z Thursday...lingering MVFR to IFR snow
showers possible...though conditions improving to VFR.
12z Thursday through 00z Sunday...generally VFR with isolated/scattered
snow showers possible...especially at kslk.
00z Sunday through 00z Monday...MVFR/IFR snow likely.