Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
141 am EDT Wednesday Mar 12 2014
a relatively quiet evening will give way to a significant winter
storm for Wednesday...Wednesday night...and into Thursday. Snow
will begin from west to east early Wednesday morning...and will
become heavy at times Wednesday afternoon. Snow showers will
linger across the region into Thursday afternoon. Parts of
southern Vermont could see a mix of precipitation for a time
Wednesday afternoon. In addition to the snowfall the storm system
will usher in colder temperatures Wednesday night and
Thursday...with wind chills from 0 to -20.
Near term /until 8 am this morning/...
as of 108 am EDT Wednesday...no significant changes to
expectations for the rest of the overnight based on a review of
early 00z/12 guidance...with the only adjustments that were made
to the forecast was to better match temperature trends overnight.
Temperatures to trend downward overnight as cold front to north
sags southward. Considerable cloudiness overspreading region in
advance snowstorm later today.
Short term /8 am this morning through 6 PM Thursday/...
as of 330 PM EDT Tuesday...the intensifying low pressure system
(990 mb) coming out of the Ohio Valley during the day Wednesday
will move eastward to the New Jersey/Pennsylvania area Wednesday
evening strengthening further to 980 mb. This will peak in
intensity Thursday morning off of the New England coastline
between 975 - 980 mb before pushing out of the region. This is a
very favorable track for heavy snow in northern New York and
Snow will overspread the entire region Wednesday morning as warm
air advection increases over the area and thermal gradient
continues to tighten. The snow will continue through Wednesday
night and even into Thursday as backside deformation band sets up
over the north country. The snow will peak in intensity from
Wednesday afternoon and through Wednesday night (generally 18z -
12z)...before gradually tapering off during the day on Thursday.
There may even be some thunder-snow Wednesday evening and
Wednesday night as some elevated cape is noted in forecast
soundings for parts of central and southern Vermont.
The heaviest snow will likely fall across central Vermont as it
will lie just northwest of the 850 mb low track and where the
best deformation and frontogenetic forcing sets up. There is
concern for some mixing across southern Vermont as 850mb-700mb
warm layer encroaches on the region. This has been shown with
sleet in the forecast for extreme southern portions of Rutland
and southeastern Windsor counties. Further trends will need to be
monitored to see if mixing will need to be introduced further
north. Expecting relatively limited shadowing effects with
generally northeast winds...however it won't be non-existent.
Best orographic enhancement will be across the eastern slopes of
the Green Mountains and the Northeast Kingdom for Wednesday and
first half of Wednesday night before shifting into the Champlain
Valley and parts of the western slopes as winds turn more
north/northwesterly late Wednesday night and on Thursday. Some
Champlain Valley channeling may increase effects in the Champlain
Valley late Wednesday night and early Thursday morning. Snow-
liquid ratios will start low Wednesday (generally 10:1) in warm
air advection snow...gradually increasing through the storm as
temperatures fall and snow-growth zone deepens. However low level
winds of 30-40 knots will tend to limit snow ratios as well.
Ramped up to a maximum of 15-17:1 on the backside Thursday morning.
All of this equates to a continued forecast of 10-20" (with
locally higher amounts) of snow for much of northern New York and
most of Vermont...with 6-10" in the Saint Lawrence valley.
Other concern will be developing strong north/northeast winds
later Wednesday...Wednesday night...and into Thursday...with
gusts from 20-35 miles per hour. This will lead to considerable blowing and
drifting of snow...and brief whiteout conditions. Temperatures
will also undergo a significant drop during the storm...starting
in the upper 20s and lower 30s Wednesday morning...falling
through the 20s during the day and into the single digits to near
10 degrees by late Wednesday night and Thursday morning. Highs on
Thursday will only rebound in the teens to near 20 for Thursday
afternoon. This combination of cold temperatures and strong winds
will lead to wind chills of 0 to -20 degrees late Wednesday night
and Thursday morning.
Long term /Thursday night through Tuesday/...
as of 346 PM EDT Tuesday...no major precipitation systems
expected. Temperatures briefly above average Saturday...but
trending back well below normal early next week (sunday-tuesday).
Deep surface cyclone departs northeastward across the Canadian Maritimes
late Thursday with surface ridge axis building from west-east into
the north country during Thursday night. Pressure gradient
remains moderately strong early...and as a result winds may
remain a bit gusty Thursday evening (nw 10-15 mph).
However...winds will diminish toward midnight as ridge axis
builds in and planetary boundary layer stabilizes. With mainly clear skies and
expected fresh and deep snow pack...will have ideal radiational
cooling conditions after midnight. This will aid in very cold
early morning lows near zero and locally -5f to -10f in the
Adirondacks and far northestern Vermont.
Active northern stream brings a series of weak shortwave troughs
and associated surface lows across the Great Lakes into the northeast
Friday and Saturday. Increasing clouds expected Friday morning
with 30-40 probability of precipitation for light snow shower activity in the afternoon
and evening. Snow amts generally a dusting to 2"...highest over
the higher terrain. High temperatures generally in the upper 20s to lower
30s. A trailing cold front brings rain/snow showers
Saturday...followed by a colder air mass for Sunday and Monday.
Temperatures reach the lower 40s at lower elevations ahead of the front
Saturday...but northwest winds and low-level cold air advection result in highs only in
the upper 20s Sunday and in the upper teens to lower 20s for Monday
with gusty north-northwest winds. It continues to appear next southern stream low
pressure system will pass out to sea well to our south
Mon/Tue...so forecast continues to indicate below normal temperatures
and dry for Monday into Tuesday.
Aviation /06z Wednesday through Sunday/...
through 06z Thursday...generally VFR with unrestricted visibility through
12z. Winds light and variable through 12z. Low pressure approaching
from the Ohio Valley brings steady snow to the region beginning
11-12z across northern New York and 12-14z across the Vermont taf sites. Snow
trends moderate in intensity 16-18z with LIFR to vlifr all areas.
Major impact to aviation ground operations by afternoon.
Outlook 06z Thursday through Sunday...
06z Thursday - 18z Thursday...major snowstorm brings LIFR/vlifr with major
impact to aviation ground Ops. North winds gusting to 30 kts at
btv and pbg with visibility below 1/4sm at times. Ne25-35kts at kmss.
Late Thursday...improving to VFR conditions at all taf sites. Northwest
winds 10-20 kts.
Thursday night through Sunday...brief MVFR in snow showers Friday
afternoon and evening. Scattered rain and snow showers
Saturday...with brief periods of MVFR/IFR. Frontal passage brings
gusty northwest winds Saturday night into Sunday...20-25 kts at times.
Isolated -shsn...mainly for slk/mpv.
Vermont...Winter Storm Warning from 8 am this morning to 8 PM EDT
Thursday for vtz001>012-016>019.
New York...Winter Storm Warning from 8 am this morning to 8 PM EDT
Thursday for nyz026>031-034-035-087.