Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
335 PM EST Sat Dec 3 2016
terrain drive snow showers in northwest flow persists into
tonight, with valleys seeing more scattered activity.
Precipitation tapers off on Sunday with a brief period of quiet
weather extending into Sunday night. The potential for light
snow returns early Monday through Monday evening. A more active
pattern develops by the middle and later part of next week as
low pressure and deeper moisture push into the region.
Near term /through Sunday/...
as of 335 PM EST Saturday...persistent cloud cover and terrain
driven snow showers under cold air advection in northwest flow
will keep temperatures from falling much into the teens and
upper 20s tonight. Snow showers will diminish in coverage
tonight, but persist in the upslope snow showers. Still some
concern for possible fzdz as drying occurs aloft and moisture
sinks below the snow growth zone for early morning Sunday. Have
therefore included slight chance for fzdz from 09z-12z based on
BUFKIT thermal and moisture profiles. Only kept it at slight
chance since depleting moisture could result in an end to precip
altogether. Additional snowfall accumulation throughout the
near term expect a dusting below 1000 ft, generally less than 1
inch for elevations 2000 ft and below, with 1-4 inches possible
above 2000 ft.
On Sunday the snow will taper off but clouds are expected to
persist under strengthening inversion. Max temperatures will
range from the low 20s to mid 30s.
Short term /Sunday night through Monday night/...
as of 335 PM EST Saturday...upper trough will move into the
area early Monday morning and exit the area to the east Monday
evening. This is not a strong system, but dynamic forcing and
low level warm air advection will move across the area. This
will provide sufficient lift for light precipitation to move
into northern New York after midnight Sunday night and across
Vermont during the morning hours on Monday. Thermal profile
during this time period supports precipitation to be in the form
of light snow with snowfall amounts ranging from a half inch in
northeast Vermont to 1 to 2 inches elsewhere. The light snow
will begin to taper off Monday afternoon and temperatures in the
larger valleys will get into the mid 30s and this may allow for
some light rain to mix in. Dynamic support and warm air
advection moves east Monday night and precipitation should
quickly turn to light snow showers before ending around
Long term /Tuesday through Saturday/...
as of 246 PM EST Saturday...large scale pattern supports
developing mid/upper level trof across the NE Continental U.S. With several
systems expected to impact the forecast area. This will support
an increasing snow pack across the mountains...with
temperatures trending below normal by the end of the week.
Models in pretty good agreement with the strongest system with a
period of precip impacting our region Thursday into
Friday...followed by a period of backside upslope snow and low
level cold air advection. Below are some daily thoughts and
Tuesday...very quiet with building mid/upper level ridge and
1024mb surface high pres directly overhead. Forecast challenge
will be if any low level moisture is trapped below developing
thermal inversion to produce low clouds...lately this has
occurred even when soundings are dry. Will mention partly sunny
with progged 850 to 925mb thermal profiles supporting near
normal temps for early Dec...mainly upper 20s mountains to near
40f warmer valleys.
Wednesday...both GFS/European model (ecmwf) show mid/upper level ridge breaking
down...as southern stream short wave energy and a ribbon of
enhanced 850 to 500mb moisture moves from southwest to northeast
across our region. The energy and moisture seem to be shearing
out in the confluent/fast flow aloft across the NE conus...so
only anticipating a period of mainly light snow activity. Trends
will be monitored for a stronger system with greater moisture
advection from the Gulf of Mexico...as current system is now
beginning to be sampled better. Models have been consistent
showing this system remaining unphased with northern stream
energy over the northern plains. Latest guidance shows both
850mb and 925mb temps <0c...supporting all snow...but thinking
enough boundary layer warming will occur in the Saint Lawrence
and Champlain valleys to support a mix of rain and snow toward
18z. Dusting to several inches expected in the mountains...will
mention likely pops...but thinking impacts will be minimal.
Thursday/Friday...this period features the greatest uncertainty
as large scale pattern change occurs with modify Arctic airmass
and a period of precip. Deep mid/upper level trof will be
developing across the northern plains with the coldest airmass
of the season expected to impact much of the eastern conus. As
this trof deepens potent short wave energy and associated Arctic
boundary will be moving across the central Great Lakes and
eastern conus. GFS/CMC show short wave energy enhancing
cyclogenesis over eastern New England...which helps to develop
precip along the Arctic boundary. This idea would support a
widespread accumulating snowfall for most of the area.
Meanwhile...latest 12z European model (ecmwf) shows an unphased system and no
surface low pres developing....supporting a period of rain/snow
showers with fropa. Given the expected deep trof
amplification...progged potent short wave energy...and magnitude
of cold air advection...will trend toward the higher precip
solution and mention likely pops. This scenario of a very cold
air mass interacting with very warm waters over the western
Atlantic will be monitored closely...for potential greater
impacts. Stay tuned. Temps start near normal for Thursday...but
progged 850mb temps btwn -11c and -13c by 12z Friday...support
highs only in the teens mountains to upper 20s/lower 30s...with
brisk northwest winds.
Saturday...models fall back into better agreement late Friday
into Saturday with a favorable period of accumulating upslope
snow. Deep mid/upper level trof...along with leftover 850 to
500mb moisture and favorable northwest 850mb winds of 40 to 50
knots...all point to a period of terrain driven upslope snow.
Will continue to mention likely pops in the mountains Friday
night into Saturday...with temps only in the teens mountains and
20s in the valleys for highs Saturday.
Aviation /20z Saturday through Thursday/...
through 18z Sunday...widespread MVFR conditions persist across
the north country as combination of northwest flow and plentiful
moisture continue to produce snow showers. Periods of IFR
possible in snow showers. While areal coverage of snow showers
will gradually decrease, focusing around the higher terrain and
western slopes, expect MVFR conditions to persist into Sunday
morning. All but slk and mpv expected to improve to VFR in the
mid to late morning hours, but low VFR deck of clouds will
persist under strong inversion.
Snowfall totals throughout the period will generally be a
dusting to two tenths of an inch in broad valley locations: mss,
pbg, btv, rut. Mpv and slk can expect about a quarter inch to
three quarters of an inch through 18z Sunday.
Outlook 18z Sunday through Thursday...
18z Sunday through 12z Monday...trending mainly VFR with high
pressure building into the area.
12z Monday through 12z Tuesday...trending broken/overcast VFR/MVFR cigs
with scattered areas of light rain or snow, mainly at kmss/kslk.
Brief IFR possible at these terminals with this activity.
12z Tuesday through 06z Wednesday...VFR/high pressure.
06z Wednesday Onward...trending MVFR/IFR in rain/snow showers.