Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
644 PM EST sun Nov 29 2015
any light snow showers will be coming to an end this evening before
clearing skies develop overnight and temperatures cool into the
teens and 20s by morning. A building area of high pressure will
produce mostly sunny skies on Monday with slightly below normal
temperatures the next weather system arrives late Tuesday into
Wednesday. A brief wintry mix is possible with the initial surge
of moisture...but expect mostly rain with this event as
temperatures warm back above normal.
Near term /until 6 am Monday morning/...
as of 644 PM EST Sunday...steadier light snow has tapered off and
there will just be some lingering light snow showers through about
10:00 PM before finally ending. North to northeast low level flow
is bringing drier air down from Canada and this will slowly erode
the clouds...but not until after midnight. Cold air advection
overnight will allow temperatures to fall into the teens and 20s.
Short term /6 am Monday morning through Tuesday night/...
as of 325 PM EST Sunday...surface high pressure and building
ridge aloft on Monday ahead of our next system will result in
mostly sunny skies and dry conditions. After a cold start
temperatures will warm back into the upper 20s to upper 30s on
Monday very close to normal for late November. Another cold night
is expected on Monday night with surface high pressure slowly
shifting into northern Maine. Thinking the coldest temperatures
near 10f will be across the Northeast Kingdom with l/M 20s in the
Champlain Valley. Expect a sharp thermal inversion to develop as
prognosticated 850 mb temperatures climb to near 0c by 12z Tuesday...supporting
temperatures warming to near freezing on the mountain summits by
On Tuesday clouds will increase quickly with rain arriving by early
afternoon. Still noting some timing differences in the arrival of
initial surge of warm air advection moisture with the GFS about 3 to
5 hours faster than the NAM. GFS tends to capture arriving of warm
air advection moisture and lift better so will use in grids. Thermal
profiles show 850mb temperatures near 0c when precipitation is
arriving...but these quickly surge well north of our region by 00z
Wednesday. However the combination of evaporational cooling and soundings
showing a cold layer between 1000 and 2000 feet with temperatures
between -1c and -3c will result in a brief 1 to 2 hour window of
freezing rain and sleet when the precipitation arrives on Tuesday
afternoon....especially in the mountains of New York and Vermont.
Any ice accumulation will be very light. Quantitative precipitation forecast with initial surge of
lift will be between 0.05 and 0.25 with the highest amounts over the
southeast upslope regions of The Greens/dacks.
Greater uncertainty develops on Tuesday night associated with
position...track...and development of secondary area of low pressure
along the coast. NAM is the most aggressive with this feature and
tracks it close enough to the coast to cause another surge of
precipitation overnight Tuesday...especially for central/eastern
and southern Vermont. Meanwhile...the GFS is much less suppressed with
secondary system and keeps this feature well off the coast with
limited impacts. Will trend toward a GFS solution and keep higher
probability of precipitation/quantitative precipitation forecast with frontal passage after midnight Tuesday into Wednesday
morning. Thermal profiles overnight will continue to warm and
support all rain through 12z Wednesday. Temperatures will hold steady
or rise some overnight in the middle/upper 30s to middle 40s. Some
shadowing is possible across the Champlain Valley given prognosticated
850mb flow of 35 to 45 knots from the southwest overnight. Will
add this detail into the grids. Thinking additional quantitative precipitation forecast will range
between 0.10 and 0.30 associated with frontal passage.
Long term /Wednesday through Sunday/...
as of 228 PM EST Sunday...more showers Wednesday as upper low and
surface cold/occluded front make their eastward into forecast
area during the day and then pass east of the area Wednesday night
into Thursday morning. Cooling temperatures aloft Wednesday afternoon
and evening...so a mix or changeover to some snow expected in the
mountains. With passage of upper low later Wednesday night...deep
northwest flow and cold air advection combined with sufficient
low-middle level moisture will allow for any showers to transition to
mainly snow showers before tapering off. Bulk of activity by this
time will be orographic in nature...favoring the western slopes.
Forecast area expected to remain under cyclonic flow on Thursday
from a deepening low pressure area over the Canadian Maritimes on
Thursday. Have continued with slight to low chance probability of precipitation for snow
showers on Thursday...mainly over the higher elevations of the
Adirondacks and Green Mountains. Expect some minor snow
accumulations Wednesday night into Thursday over the higher
terrain. Any lingering snow showers will come to an end Thursday
afternoon. Dry conditions with some clearing will follow for late
Thursday into Thursday night as a ridge of high pressure builds
into the region. Disturbance in northwest flow aloft may bring
some clouds and slight chance for a few rain/snow showers Friday.
Large area of high pressure both at surface and aloft will then
build in for next weekend...with fair and dry conditions expected
along with milder temperatures.
Aviation /00z Monday through Friday/...
through 00z Tuesday...widespread MVFR/VFR ceilings will persist
through midnight before slowly decreasing in areal coverage
through 12z. After 12z VFR conditions will exist through the
remainder of the period. North to northeast winds overnight will
generally be less than 10 knots...then shift to the south and
southeast after 12z.
Outlook 00z Tuesday through Friday...
00z Tuesday through 18z Tuesday...VFR under high pressure.
18z Tuesday through 18z Thursday...VFR conditions deteriorating to
MVFR/IFR as low pressure system brings rain to the region Tuesday
afternoon into Wednesday. Rain transitions to snow showers Wednesday
night into Thursday morning before ending.
18z Thursday Onward...mainly VFR.