Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
646 PM EST Thursday Dec 25 2014
an area of weak high pressure will build into the north
country overnight...but with lots of leftover moisture around expect
plenty of clouds. Temperatures with clouds and breezy west winds
will stay above freezing in the valleys and drop into the 20s in the
mountains. A weak cold front will produce mainly mountain rain and
snow showers on Saturday into Sunday...along with much colder
temperatures by early next week.
Near term /until 8 am Friday morning/...
as of 646 PM EST Thursday...have raised min temperatures up a few
degrees in several locations overnight...based on the latest GFS
lamp guidance and the 18z GFS MOS guidance. Also...combination of
cloud cover and gusty winds across the region overnight should
provide enough mixing to help to keep temperatures up as well.
Otherwise...no other changes to the forecast at this time.
Previous discussion from 1214 PM EST Thursday...visible satellite pics
this afternoon show plenty of clouds across the NE Continental U.S. And upstream
over the Great Lakes. Given the anticylonic follow around surface high
pressure to our south...expect plenty of low clouds across our County Warning Area
tonight. NAM BUFKIT soundings at slk shows plenty of moisture
trapped blw a developing subsidence inversion between surface and 3000
feet. In addition...favorable westerly trajectory will help advect
Lake Ontario moisture into the dacks along with the upslope follow
may produce a few light snow showers. A dusting to 1 inch of snow
is possible overnight into Friday morning across the mountains soundings
show very limited moisture in the favorable snow growth
region...so anticipate more snizzle or rime across the mountain summits
overnight into Friday. Temperatures will range from near 20f mountain summits to
M/u 20s midslope areas to middle 30s warmer valleys (cpv/slv).
Short term /8 am Friday morning through Saturday night/...
as of 323 PM EST Thursday...very quiet weather anticipated Friday through
Saturday night with only light chances for mainly mountain rain/snow
showers during this time period. Large scale setup continues to show a
middle/upper level ridge along the East Coast with surface high pressure over
the Middle Atlantic States. This will produce a fast westerly follow aloft
across our County Warning Area...with limited deep layer moisture.
However...soundings continue to support plenty of low level moisture blw
subsidence inversion on Friday into Saturday...and given the
shallow nature of the moisture...thinking higher mountain summits may
experience some sunshine on Friday...especially above 3000 feet.
Also...thinking a few breaks in the overcast will be possible in the
cpv/lower CT River Valley associated with westerly downslope
follow...and latest 12z soundings showing moisture thinning
significantly toward 18z Friday. Thermal advection behind initial
cold front is mainly aloft with prognosticated 850 mb temperatures dropping between -3c
and -5c...resulting in summits cooling...but valleys holding in
the 40s. For Friday...thinking a similar type scenario will play
out...with valleys warming into the u30s to m40s...while summits
hold in the upper 20s to lower 30s. Winds will be generally
southwest to west at 5 T 15 knots with some higher gusts in the
aligned valleys and mountain summits.
Friday night-Saturday night...on Friday night into Saturday both
GFS/NAM show weak 500 mb vorticity in westerly follow aloft crossing near the
international border along with a weak ribbon of enhanced 850 to
500mb relative humidity...which with favorable westerly low level follow will produce some
light rain/snow showers mainly across the mountains will mention chance probability of precipitation
with quantitative precipitation forecast values <0.10" and snow levels above 1000 feet. Snow
accumulations will range once again between a dusting to 2 inches...across
the northern dacks and along The Spine of Jay Peak to Montana Mansfield.
Very light and limited quantitative precipitation forecast anticipated in the valleys with only a
few sprinkles or flurries possible. Another weak system in the fast
follow aloft impacts the region on Saturday night into Sunday with
another shot of light rain and snow showers. Not expecting much quantitative precipitation forecast
or snowfall. Temperatures through this period will be above normal with lows
mainly in the 20s mountains to 30s valley and highs in the 30s to middle
Long term /Sunday through Thursday/...
as of 233 PM EST Thursday...biggest issue in extended period is
return to below normal temperatures behind cold front lingering
probability of precipitation on Sunday with exiting shortwave trough and surface cold
front. Low level flow turns northwest and cold air advection
regime to persist through middle week. Upper flow is westerly in
broad trough over the east with northern branch of the jet stream
near or north of the Canadian border. Surface high pressure behind
the front into middle week on an east-west axis with center of
surface high plunging south into central Continental U.S..
925 mb temperatures around 0c on Sunday fall to negative teens by
Wednesday. From about Tuesday Onward low level winds turn more
westerly with neutral temperature advection and no additional cooling or
warming for that matter. Gridded maximum/min temperatures for Tuesday and Wednesday
colder than previous run...and weren't supported by 925 mb temperatures
so adjusted those up a degree or two. From middle week on westerly
low level flow and cold temperatures off Lake Ontario will generate lake
effect clouds and snow. Models did not pick up on lake effect
scenario and had to draw in probability of precipitation for lake effect snow in the
western Adirondacks and far west St. Lawrence Valley.
Aviation /00z Friday through Tuesday/...
through 00z Saturday...primarily VFR/MVFR conditions due to
ceilings through the period. Except for a periodic -shsn at kslk
it should be dry through the period. Gusty west/southwest winds
with gusts 20+ knots will gradually decrease this evening and
overnight...becoming southwest 5-15 knots on Friday.
Outlook 00z Saturday through Tuesday...
00z Saturday-18z Saturday...brief ridge of surface high pressure
builds into the region. Mainly VFR expected...but periods of
lingering MVFR still possible.
18z Saturday-00z Monday...a chance of mainly rain showers along with
MVFR ceilings possible with frontal passage...especially mss/slk/mpv.
00z Monday Onward...mainly VFR with high pressure building in.
a lake Wind Advisory remains in effect through midnight tonight.
Southwest winds from 15 to 25 knots will continue through this
evening...before decreasing to 10 to 20 knots overnight. Waves
from 1 to 3 feet will gradually subside overnight.
marine...weather forecast office btv