Scientific Forecaster Discussion
fxus61 kbtv 072348
Area forecast discussion
National Weather Service Burlington Vermont
648 PM EST Sat Dec 7 2019
isolated to scattered snow showers are expected through this
evening, but clearing skies and lighter winds will result in
cool conditions overnight. A warm front with more clouds and
scattered snow showers develops on Sunday across the higher
summits of the north country. Brisk winds will help push much
above normal temperatures into the region by Monday, along with
widespread threat for rain showers. Some pockets of freezing
rain is likely on Monday morning, which will lead to a slippery
commute, especially east The Greens. After another warm day on
Tuesday, much colder air returns for midweek, along with
additional chances for mainly mountain snow showers.
Near term /through Sunday night/...
as of 556 PM EST Saturday...just a few refinements to the
forecast based on trends. Looks like drier air over northern New
York and stabilizing lapse rates have brought the snow showers
over the northern Adirondacks to an end. However...still looking
at snow showers scattered across Vermont with the greatest
concentration along the west slopes of the Green Mountains.
Froude number indicates blocked flow should persist all
night...but stabilizing lapse rates and drier of the lower
levels should finally bring snow showers to an end. Have tweaked
forecast to reflect this idea. Rest of forecast in good shape
and remains unchanged.
very changeable temps expected in the this period, along with
breezy conditions developing on Sunday/Sunday night, and some
pockets of freezing rain possible toward 12z Monday. Surface
analysis places 1031mb near kbuf this aftn with cyclonic
northwest upslope flow continuing across our fa. This favorable
upslope flow and some shallow moisture in the dzg has resulted
in snow showers across the trrn most of today. Expecting this
activity to decrease quickly by sunset, as stability increases
and shallow moisture dissipates, allowing for some partly to
mostly clear skies for a period of time tonight. Clear skies,
light winds and fresh snow will result in cold overnight lows
ranging from -5f slk/nek to lower teens cpv. Increasing
southerly gradient and 850 to 500mb moisture fields aft 06z will
limit temps from completely bottoming out. Sunday, guidance
shows ribbon of enhanced 850 to 700mb rh, along with some 700 to
500mb uvv's as moderate to strong waa develops. Thinking qpf
will be light, but a few snow showers are likely from northern
New York into the mountains of Vermont btwn 15z-21z Sunday. Accumulations
will be >1.0 and mainly confined to the higher summits. The next
story will be breezy to gusty winds developing as gradient
sharpens quickly between departing 1031 mb high pres and
developing low pres. 925mb to 850mb wind fields of 45 to 55
knots develops, with soundings supporting bottom of the mixed
layer winds in the 30 to 35 knot range, especially in channeled
south/southwest to north/northeast oriented valleys. Expecting
gusts up to 35 mph cpv/slk with near 40 mph possible over the
lake. Temps response with southerly flow and warm into the upper
20s to mid 30s, but gusty winds will result in much cooler feel
like values. Sunday night deeper 850 to 500mb moisture
increases acrs our western/northern cwa, while a weak embedded
5h vort crosses from southwest to NE acrs our fa. This
energy/moisture will help to increase the chcs for additional
showers toward 12z Monday. Given recent cold spell and
anticipated cold ground temps, expect pockets of freezing rain,
even if temps are in the l/M 30s. A slippery Monday morning
commute is possible and will highlight in the hazardous weather
outlook. Temps remain steady or slowly warm overnight in the
wider valleys with lows mainly upper 20s to mid 30s.
Short term /Monday through Monday night/...
as of 245 PM EST Saturday...a warm front will lift through the region
Monday morning with southwesterly flow aloft advecting both moisture
and much warmer air into the north country. While the isentropic
lift looks unimpressive along the leading edge of the warm front, as
we continue to advect in deeper moisture, the jet dynamics in the
mid and upper levels begin to become increasingly favorable for
large scale ascent. As this happens, rainfall will become rather
widespread with many locations seeing either rain or freezing rain
during the morning commute on Monday. Temperatures Monday morning
will be a bit tricky and will be highly dependent on the degree of
warm air advection. Even if temperatures end up being a degree or
two above freezing Monday morning, the cold soaked roads from the
cold temperatures this weekend will be able to accrete some ice.
Temperatures will quickly warm into the mid to upper 30s by 11 am on
Monday which will put an end to any chances for freezing rain. Based
on the current forecast, it looks like anywhere from 0.01 to 0.05
inches of freezing rain will be possible Monday morning.
Precipitable water (pwat) values will increase to 0.80 to 0.85
Monday afternoon as temperatures warm and deep moisture continues to
advect into the region. This will put US above the 90th percentile
for the day which shows how anomalously moist this air mass will be.
Southwesterly winds in the low levels will increase as the gradient
between a departing high pressure and a developing surface low
moving toward the St. Lawrence Valley increases. The low level jet
will strengthen to 40 to 50 knots during the afternoon hours which
will begin to downslope the Champlain Valley. This should limit
rainfall in the Champlain Valley while maximizing rainfall amounts
across the western slopes of the green and Adirondack Mountains.
Overall, rainfall totals will range from a third of an inch across
the Champlain Valley to about three quarters of an inch across
southern Vermont. We are monitoring the potential for some river
rises in response to melting snow and rainfall but it looks like
most rivers will remain within bankful given the latest ensemble
river forecasts. However, should we get more rainfall than we
currently have forecasted, greater rises will be possible on area
Long term /Tuesday through Saturday/...
as of 245 PM EST Saturday...we will still be under the influence of
southwesterly flow Tuesday morning which will prevent the lows from
the Monday night from cooling off too much. Temperatures during the
pre-dawn hours will likely linger in the mid to upper 30s while rain
begins to taper off. A strong cold front will move into northern New
York around sunrise and work its way eastward through the north
country during the morning and early afternoon hours. This should
allow temperatures to cool throughout the day following the frontal
passage with the possibility of a few snow showers developing
underneath an upper level short wave and associated jet streak.
Overall, it should be dry behind the front with lows Tuesday night
expected to fall into the mid teens to lower 20s.
A Good Lake effect snow pattern sets up on Wednesday with a long
westerly fetch developing across Lake Ontario an a very cold air
mass sitting on top of a Warm Lake. While it's hard to get a good
grasp on the placement of this feature, it looks like portions of
Essex and Franklin counties in New York could see some decent
snowfall before winds begin to shift from the west to the northwest
Wednesday night. Drier weather will then return on Thursday with a
1040+ mb high situating across the north country. Temperatures on
Thursday will be well below normal with temperatures struggling to
reach 20 degrees in the deeper valleys with mid teens elsewhere.
Friday and Saturday look like they could be wet across the northeast
with a low pressure system tracking somewhere near benchmark. There
isn't really any run-to-run consistency at this time so it's hard to
say whether it will impact US and if so will it bring rain or snow.
Aviation /00z Sunday through Thursday/...
through 00z Monday...overall looking at VFR conditions through
much of the period as little in the way of cloud cover is
expected. However...there will be one exception. Lingering
lower clouds and snow showers will likely produce MVFR to IFR
conditions for a short period of time through 03z at kslk and
kmpv. The other item of note will be the winds and the
development of low level wind shear. Winds will be light through
about 12z...then increase through 18z from the south and
southwest. Expect gusts as high as 15 to 20 knots during this
period with a few higher gusts after 18z. Stronger flow aloft
begins to move over the region after about 15z and persists
through the remainder of the period. Expect south to southwest
winds at 2000 feet reach speeds in the 40 to 50 knot range which
will create low level wind shear conditions.
Sunday night: mainly VFR, with local MVFR possible. Chance shra,
chance freezing rain.
Monday: mainly MVFR, with areas IFR possible. Definite ra, likely
Monday night: mainly IFR, with areas MVFR possible. Definite ra,
chance rain showers.
Tuesday: mainly MVFR, with local VFR possible. Chance shra,
Tuesday night: mainly VFR, with local MVFR possible. Chance shsn.
Wednesday: VFR. Chance shsn.
Wednesday night: mainly VFR, with local MVFR possible. Slight
Thursday: VFR. No sig weather.