Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
717 PM EDT Friday Mar 14 2014
weak surface low pressure centered over the northern Great Lakes
region will move eastward tonight and pass north of the
international border during Saturday morning. Winds will remain
gusty from the south and southwest this evening and overnight.
Scattered light rain or snow showers are possible late tonight
into Saturday morning associated with this low pressure system.
More organized snow showers or snow squall activity will then
occur as a trailing cold front shifts southeastward across the
region Saturday afternoon. This cold front Ushers in much colder
air on gusty northwest winds Saturday night. Cold and dry weather
is expected with high pressure in control Sunday through Tuesday.
High temperatures Sunday and Monday will only be in the teens to
Near term /until 7 am Saturday morning/...
as of 627 PM EDT Friday...another quick update to add areas of
blowing snow through the evening hours and into tomorrow as gusty
winds continue. Highest threat of blowing snow this evening on
east-west oriented roadways in Vermont where temperatures are
initially colder. Otherwise only changes as of 600 PM were to
match current trends in temps/dewpoints. Temperatures have surged into
the lower and middle 40s across the slv early this evening with other
areas from the dacks eastward continuing to slowly climb. With
gusty southerly flow continuing all night...expect readings to
remain steady or slowly climb through (or into) the 30s...with
areas across the slv holding near the 40 mark. Rest of forecast
unchanged with prior afternoon discussion below. Have a great
warm front lifting northeastward across the north country is bringing
overcast skies but limited moisture and low- level convergence is
keeping conditions generally dry. Increasing pressure gradient
will result in continued moderately strong southerly winds of 15-25
miles per hour...with gusts to 30-35 miles per hour. Highest gusts likely in the
Champlain Valley with localized valley channeling. Temperatures should
continue to slowly rise overnight owing to clouds and windy
conditions. Temperatures generally rising into the 30s areawide...and
generally above freezing west of the Green Mountains
In terms of precipitation...low chances for the first half of
tonight with limited low-level convergence and boundary layer
moisture. Recent WV imagery indicates a well-defined shortwave
trough across the central Great Lakes at 19z...which will continue
to move eastward. This trough and associated differential cva will
provide better forcing for ascent after 06z. The low-level SW flow
will result in orographic shadowing in the Champlain
Valley...where we/ve held probability of precipitation around 20 percent with little or no
precipitation expected. Elsewhere...probability of precipitation increase to 40-60 percent after midnight
with scattered rain/snow shower activity. Quantitative precipitation forecast amts generally less
than 0.10" tonight...highest across southern St. Lawrence County into
the Adirondacks per model consensus. Could see a dusting to an
inch of snow in spots across southern St. Lawrence County into southern
Franklin County...and also across the Green Mountains all in all...not
expecting any significant impacts.
Short term /7 am Saturday morning through Sunday night/...
as of 311 PM EDT Friday...surface low passes north of the area Sat
morning with progressive 700-500mb vorticity moving through around 12z.
Anticipate a chance of rain/snow showers during Saturday
morning...especially across the higher elevations. Temperatures should
briefly reach the upper 30s to lower 40s for a time late Saturday
morning into the early afternoon hours across the lower elevations.
This will result in some modest melting of snow...only to refreeze
later in the day/evening...
Following a mild 1st half of the day...trailing Arctic boundary
reaches the St. Lawrence Valley around 19z...and shifts through northern Vermont
20-23z. This boundary is associated with modest cape (around 50
j/kg) and significant 925mb frontogenetic forcing. The btv snow
squall parameter indicates potential snow squall activity along the
boundary with strong low-level forcing and instability...and that will
be something to watch late in the day into the early evening hours
for the northern 1/3rd of the forecast area. Could see a quick d-2" with
gusty northwest winds and rapid fall in temperatures...as is indicated by btv
local WRF runs and 12z NAM following frontal passage.
Saturday night: in the wake of the Arctic cold front...orographic
snow showers will continue across the northern Adirondacks and
central/northern greens through at last the first half of the night.
Low-level lapse rates are rather steep with the cold air advection...so Don/T
anticipate much orographic blocking. Snow showers that do occur
should be confined to the immediate western slopes...summits...and
points several miles downstream. May see an additional 1-2" across
the higher terrain. Temperatures will fall significantly with the
strong low-level cold air advection Saturday night. Temperatures by 12z Sunday likely
8-12f across central/northern Vermont...and close to zero across northern New York. Lows
in the middle-upper teens with later arrival of colder air across
Rutland/Windsor counties. Northwest winds 10-20 miles per hour will yield wind chill
values of 5 to 15 below across northern Vermont and New York late Saturday night
into early Sunday am.
Arctic air mass in place Sunday with moderate north-northwest winds with
gradient still in place on eastern periphery of high pressure
building eastward across the Great Lakes. Winds generally 10-15 miles per hour
with gusts to 25 miles per hour. Deep-layer relative humidity fields suggest mostly sunny
conditions...and March sun angle will help offset the cold air
mass to some extent. Mav-MOS may be a bit too cold considering the
insolational effects...so have Learned toward warmer met guidance.
Still...only looking at highs generally in the middle-upper teens...except
low- middle 20s across Rutland/Windsor counties with later arrival of
colder air mass and some adiabatic/downslope warming possible into
the CT River Valley.
Sunday night appears clear and cold with high pressure building
across southeastern Ontario and southwestern Quebec. Diminishing wind should aid in
good radiational cooling. Lows zero to 10 below most
sections...except zero to +5 in the immediate Champlain Valley and
valleys of S-central Vermont.
Long term /Monday through Friday/...
as of 243 PM EDT Friday...upper level trough over southern Quebec
departs north and east with high pressure over the north country
at the surface to start the period. Few upper level shortwave pieces of
energy will move over the area...but lack of moisture in surface cold
Canadian high will result in little more than clouds through late
Next low pressure system to approach the northeast will develop
in the Lee of The Rockies late Monday into Tuesday and track eastward
reaching the Great Lakes region late Tuesday as surface high over NE
slides eastward. Now on the western side of the ridge...southerly flow
will moderate temperatures for the middle of the week. GFS a
little more progressive with the approaching low. Expect precipitation
in the warm sector of this system to develop across the north
country late Wednesday into Thursday. By Thursday morning...the
GFS already brings the associated cold front through the
region...while European model (ecmwf) holds off until the afternoon. Some wrap around
precipitation will continue to affect the north country in the cold
Temperatures throughout the period will warm from 15-20 degrees below
normal to near normal for the middle of the week.
Aviation /23z Friday through Wednesday/...
through 00z Sunday...predominantly VFR for most of the tafs overnight
with potential for MVFR rain/snow mix at mss and slk. Cold front
sweeping through the north country Saturday brings a better chance
for light precipitation with VFR/MVFR flight categories.
Mostly middle-level clouds and gusty south winds (up to 32 kts at
btv) generally the rule so far this evening. Think any pre-frontal
precipitation overnight will remain limited to just at mss and slk. Look
for winds to still remain 10-15kts with gusts up to 25-30 kts with
a slow lowering trend in broken/overcast VFR ceilings. Cold front moves
through the north country during the day Saturday with an
accompanying wind shift to west around 10-12kts and ceilings
continuing to remain broken/overcast VFR/MVFR. Precipitation ahead of the
front likely to start as rain but gradually transition to a brief
period of light snow...though light snows may linger a little
longer at mpv and slk due to potential for upslope enhancement.
Outlook 00z Sunday through Wednesday...
Saturday night through Sunday...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
along with isolated -shsn...mainly for kslk/kmpv.
Sunday night through Tuesday...VFR with high pressure building in
at the surface.
Wednesday...VFR/MVFR in snow showers possible.