Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
319 PM EST sun Nov 29 2015
a period of light snow is expected 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 325 PM EST Sunday...through early this evening...the
combination of blocked flow with some additional low level
moisture and weak cold air advection has resulted in light snow
developing over the central and northern Champlain Valley and
parts of the mountains of Vermont/New York this afternoon. Expect this
activity to continue through early this evening...but moisture
decreases quickly by midnight. Only a dusting of snow is
expected. Have mention slight chance to chance probability of precipitation in these
Clouds and impacts on temperatures will once again be the focus for
tonight. Surface analysis shows weak cold front across northern New York
into Vermont with plenty of low clouds over our northern County Warning Area. The
combination of weak upslope flow and some increase surface to 700mb
moisture will produce a few light snow showers and flurries over the
northern mountains this evening. A dusting of snow is possible
across the northern dacks and parts of the northern greens from
Sugarbush to Stowe/smuggs to Jay Peak. Still some uncertainty about
amount of clearing after midnight. GFS shows much faster decrease in
low level moisture...while higher resolution btv4 and nam12 Show Low
level moisture lingering through 03z in the mountains. Given satellite
trends will hold onto clouds through 03z over the terrain and mention
mostly clear by 06z. The combination of clearing skies and light
winds associated with building high pressure will result in very
cold temperatures by Monday morning. Will mention lows near 10f
slk/Northeast Kingdom to near 20f Lake Champlain. If clearing
develops faster...a few colder valley locations could see low
temperatures in the single digits by Monday morning. Thinking the
1 spot off the mav for slk is a bit too cold given the conditions
and lack of snow cover.
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
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 /20z Sunday through Friday/...
through 18z Monday...VFR/MVFR ceilings expected for the rest of
today into this evening as low level moisture persists across the
north country. A period of MVFR ceilings expected this afternoon
into early tonight as moisture associated with cold front pushes
south across forecast area. As front pushes further south
overnight expect a return to VFR conditions with skies clearing
after midnight. Skies will remain clear during the day on Monday.
West winds will become northwest and then north at 5-10 knots this
afternoon/evening. Light and variable winds overnight will become
southerly 5-10 knots during Monday.
Outlook 18z Monday through Friday...
18z Monday 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.