Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
923 PM EST Thursday Dec 12 2013
reinforcing cold front will cross the area Friday
morning...accompanied by snow squalls...especially across our
northern zones during the early morning hours. Lake effect snow
will continue overnight in southern Saint Lawrence County. Wind
chill values will be 20 degrees below zero in the Adirondacks on
Friday with temperatures in the single digits and strong winds.
Temperatures remain cold through the short term...well below
seasonal normals. A fast moving low pressure system will pass
along the New England coast Saturday night bringing some more
snow to the north country.
Near term /until 7 am Friday morning/...
as of 923 PM EST Thursday...forecast remains in decent shape and
only slight adjustments to T/dew point trends through the overnight and
morning hours on Friday needed at this time. Temperatures to more or less
hold steady on light to moderate S/SW flow tonight...then slowly
fall through the day on Friday behind Arctic frontal passage. Lake Ontario
snow band now reaching its furthest northward extent into our southwestern
dacks and will hold steady state through about midnight before
sinking slowly south once again as flow begins to veer ahead of
approaching front. Snow totals in lake Snow Advisory area from 3-6
inches looks right on track per radar estimates/hourly accums so
current headlines all remain in place. Have a great night.
some modest changes to sky cover and wind gusts as we head
through the evening and overnight hours based off current
observational trends and rap/WRF data. Many areas across our
central and southern counties showing more pronounced breaks in
the clouds and given south to southwesterly flow overnight believe
this trend will continue so have adjusted cloud cover downward in
these areas. Also backed off on the degree of gustiness slightly
across central/western counties...but moreso across eastern Vermont where
planetary boundary layer has already decoupled. Feel trends will be for gradually
increasing gustiness Champlain Valley/western slopes westward through
the night as p-gradient tightens ahead of approaching Arctic
boundary...but much lighter in the valleys of eastern Vermont where planetary boundary layer
mixing will be tougher to come by. Rest of forecast in great shape
with scattered shsn becoming more numerous by later tonight in
association with approaching secondary Arctic surge. Best...most
consistent coverage/accums overnight across the southwestern dacks in
association with Lake Ontario snow band as flow backs slightly
ahead of frontal boundary. As alluded to in earlier
discussion...temperatures quite tricky given variability in planetary boundary layer
mixing processes and the degree of cloud cover but overall idea
will be for readings to range in the 5 to 15 above range by
morning. Have a great evening.
Short term /7 am Friday morning through Saturday night/...
as of 400 PM EST Thursday...aforementioned cold front will
continue to drop south across our forecast area Friday morning.
Will continue to see some squall activity from 12z through 18z as
front continues to move northwest to southeast across our
forecast area. Mainly a dusting to two inches of snow expected
with perhaps a few 3 to 4 inch readings where the squalls are
heaviest. Activity ends from north to south across our area and
high pressure begins to ridge into the area during the afternoon
hours. This drier air should bring some partly sunny skies.
Friday will be even slightly colder than today with cold air advection and temperatures
only reaching the single digits and teens. Coldest temperatures will be
in the Adirondacks...and along with strong winds associated with
the frontal passage and behind it...expect wind chill values to
reach advisory criteria...negative 20 wind chills. Maximum
temperatures will be reached early in the day and fall through
the afternoon. A Wind Chill Advisory is in effect for the
Adirondacks from 12z Friday through 00z Saturday.
Friday night will also be very cold as surface high pressure
slides southeast and over our forecast area. Cold air advection
continues but winds will die down. For this reason think we will
reach the negative 20s for temperatures but without sufficient wind will
likely have to issue an Special Weather Statement rather than a Wind Chill Advisory.
Unseasonably cold weather continues into the weekend with high
temperatures on Saturday even colder than the past couple
days...single digits to low teens expected. Clouds will increase
from the south during the day on Saturday ahead of next
approaching low pressure system. Light snow will also develop
from southwest to northeast across the region late Saturday into
Saturday night. By 00z Sunday there will be a pair of low
pressure systems...one in the Ohio River valley and one off the
middle Atlantic coast. The two lows will track northeastward
Saturday night with the low off the New England coast becoming
the stronger of the two. Model consensus is becoming better with
most models showing low passing inside the benchmark.
Temperatures will continue to be very cold...thus very fluffy
flow is expected. With up to a half an inch of quantitative precipitation forecast in some parts
of our County Warning Area...some warning level snow is expected with the most
likely area being southeastern Vermont. This is a fast moving
system and bulk of snow will fall Saturday night.
Long term /Sunday through Thursday/...
as of 300 PM EST Thursday...little change with regards to
departing storm on Sunday and overall large scale synoptic
pattern for early next week. GFS/European model (ecmwf) and ensemble members continue
to support mean trough across the NE Continental U.S. With potential for some
ridging toward the middle of next week. Models have trended slightly
closer to the coast for low pressure on Sunday with track from
eastern Long Island to just inside the benchmark by 18z Sunday.
This will result in a widespread accumulating snow event for Sat
night into Sunday...with most of the snow ending by 18z Sunday.
System continues to be very progressive in the fast 700 to 500mb SW
flow aloft...with middle level dry slot impacting our County Warning Area by early
Sunday afternoon...resulting in a overall decrease in snowfall.
Thinking storm total quantitative precipitation forecast will range between 0.20 and 0.50" across our
County Warning Area with highest values across the southeast upslope regions. Given the
very cold thermal profiles expecting very high fluff factor with
ratios between 20 and 30 to 1. This will result in a general advisory
type event with slightly higher amounts across southeast Vermont zones. Soundings
show good relative humidity in favorable snow growth region...along with some
850 to 700mb Omega...which will help in snow flake production.
Otherwise...deep layer moisture quickly shifts NE of forecast area by 00z
Monday with areas of flurries expected. Temperatures will struggle in the
teens to lower 20s on Sunday.
Both European model (ecmwf)/GFS show potent northern stream energy and closed
500 mb/7h circulation passing to our north Sunday night into
Monday...but moisture is limited. The dynamics combined with a
weak surface trough will probably produce additional snow shower
activity. Prognosticated 850 mb temperatures drop once again to near -20c by 12z
Monday...supporting much blw normal temperatures. The combination of
departing low pressure and building high pressure will result in some brisk
conditions on Monday. Next clipper like system approaches County Warning Area on
Tuesday/Wednesday with additional moisture/dynamics. Initial surface low pressure
is expected to pass north of our County Warning Area...but latest 12z Gem/European model (ecmwf)
show some secondary development across southern New England...which could result in
another brief period of light snow. Will mention high chance probability of precipitation
at this time...with temperatures warming back into the upper teens to M/u 20s in
the warmer valleys. Lows will be tricky through the period...with the
coldest temperatures on Sunday/Monday night...with readings blw zero to
Aviation /02z Friday through Tuesday/...
through 00z Saturday...composite radar loop showing lake effect
snow showers off of Lake Ontario at 00z Friday moving into the Adirondacks
at this time. Expecting areas of IFR lake effect snow showers
across portions of the Adirondacks overnight into Friday morning.
Otherwise mainly VFR conditions across Vermont and most of the
remainder of northern New York overnight. An Arctic cold front
will move into the region overnight with some areas of MVFR/IFR in
snow showers with the passage of this front. Expecting surface
wind gusts of 20 knots or greater to develop between 06z-10z Friday
with the passage of this Arctic cold front. Expecting surface
winds to diminish to 10 knots or less by 21z Friday as a ridge of
high pressure builds into the region.
Outlook 00z Saturday through Tuesday...surface high pressure with VFR
conditions 00z Saturday through 18z Saturday. Next system impacts all
our taf sites with widespread IFR conditions late Sat into
Sunday...with periods of LIFR conditions possible in the heavier
snow on Sat night. A slow clring trend is expected after 18z Sunday
with VFR conditions developing. Winds will generally be from the
north on Friday into Saturday...before shifting to the
south/southeast with some localized higher gusts possible near
Rutland on Saturday night. VFR conditions expected Monday and
Monday night as a ridge of high pressure will be over the region.
IFR/MVFR conditions expected on Tuesday as a warm front
approaching the region will bring some light snow.
New York...Wind Chill Advisory from 7 am to 7 PM EST Friday for
Lake effect Snow Advisory until 7 am EST Friday for nyz029.