Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 040029

Area Forecast Discussion
National Weather Service Burlington VT
729 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.


As of 705 PM EST Saturday...The going forecast remains in good
shape with persistent northwest unblocked flow. This is leading
to long duration powder in the mountains with not much precip
elsewhere to speak up. Froude numbers show the flow becoming
blocked overnight however RH becomes unsaturated in the -12C to
-18C layer, and so I dont anticipate much snow backing up to
the western slopes or the Champlain Valley. However there should
be enough moisture that with some orographic lift the snow
showers will persist on the mountain summits through the early
morning hours.

Previous discussion...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.


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


As of 246 PM EST Saturday...Large scale pattern supports
developing mid/upper level trof across the NE CONUS 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
forecaster perspective.

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/ECMWF show mid/upper level ridge breaking 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
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 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 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
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 /00Z Sunday THROUGH Thursday/...
Through 00Z Sunday...A mix of MVFR and VFR conditions exist as
of 00z with snow falling at SLK/MPV/RUT. Expect brief periods of
IFR visibilities in snow showers at both SLK and MPV although
drier air should be moving into SLK by 03-04z. Persistent
northwest flow and plentiful low-mid level moisture will lead to
snow showers at MPV possible through the mid morning tomorrow.
Any remaining snow showers will be focused mainly in the higher
terrain and along the western slopes of the Greens. Expect MVFR
ceilings to build in at all terminals except PBG as a low level
inversion looks to trap the low level moisture through Sunday
morning. At PBG expect the downsloping wind component to help
keep ceilings above MVFR thresholds. All sites expected to
return to VFR by late morning and by mid afternoon the temp
inversion may break down enough to lead to some possible breaks
in the cloud cover.

Outlook 00Z Sunday through Thursday...

00Z Sunday through 12Z Monday...Trending mainly VFR with high
pressure building into the area.

12Z Monday through 12Z Tuesday...Trending BKN/OVC VFR/MVFR cigs
with scattered areas of light rain or snow, mainly at
KMSS/KSLK. Brief IFR possible at these terminals with this

12Z Tuesday through 06Z Wednesday...VFR/high pressure.

06Z Wednesday onward...trending MVFR/IFR in rain/snow showers.




SHORT TERM...Evenson
AVIATION...Deal/KGM is the U.S. government's official web portal to all federal, state and local government web resources and services.