FXUS61 KBTV 221146
Area Forecast Discussion
National Weather Service Burlington VT
746 AM EDT Fri Oct 22 2021
A sharp cold front is passing through the North Country today,
ushering in seasonably cool and dry air. Cyclonic flow around an
upper level low well north of the Great Lakes will periodically
spread clouds and a few mountain showers eastward over the
weekend, otherwise weather will be quiet with areas of sub
freezing temperatures. A quasi stationary frontal boundary will
lift northward early next week supporting increasing chances for
a steady cold rain, with additional wet weather expected by the
end of the week.
.NEAR TERM /THROUGH SATURDAY/...
As of 738 AM EDT Friday...Forecast is on track with cold and dry
air filtering in behind the front in northern New York at this
hour right on schedule, with a 36 degree wind chill at
Ogdensburg indicative of the change in air mass. A few light
showers are out ahead of the front mainly up by the
International Border, with otherwise dry conditions for the
rest of the day.
A potent upper level system is currently moving through the
North Country bringing widespread showers. GOES-16 nighttime
microphysics satellite imagery shows deep clouds over the entire
region with shallower clouds just to the southwest where water
vapor imagery shows much drier air punching in behind the upper
level low. Therefore showers will not last much longer and
little if any precipitation will be along the surface frontal
passage as it moves through this morning. Additionally, the
drying aloft is already resulting in lowering clouds across the
St. Lawrence Valley and expect gray skies to persist areawide
for much of the day given the sharpening inversion as cooling
low level air undercuts relatively warm air above.
The combination of modest cold air advection on northwest wind,
cloud cover, and drier air will help make it feel much colder than
yesterday. Temperatures will fall behind the front, resulting in
midday temperatures only in the 40 to 45 range across northern New
York. In Vermont, temperatures will tick downward during the
afternoon hours after being generally steady in the 50s through the
first part of the day. Forecast soundings for tonight show the cloud
layer may persist along with continuous mixing of the boundary layer
below the inversion as low level cold air advection continues. As a
result, while temperatures will cool into the upper 20s to mid 30s
in most locations, frost will likely be patchy at most, but will
need to consider it a possibility nevertheless with the lack of
freezing temperatures so far this season.
While surface high pressure and daytime heating will erode the low
clouds, shortwave energy lifting northeastward will spread some
higher clouds across the region Saturday morning before a clearing
trend gets underway. The cyclonic west-southwest flow aloft will
support at least low chances of sprinkles or even flurries across
parts of the Adirondacks, but it will generally be a dry day with
temperatures mainly in the mid and upper 40s, or about 5 degrees
below normal, with light winds.
.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 409 AM EDT Friday...Mid/upper lvl trof prevails acrs the
northern Great Lakes into the NE CONUS during this time frame. The
core of coldest air looks to remain just north of our cwa, as fast
confluent westerly flow continues thru Sunday evening. Have
continued with schc/chc pops for late Saturday night into Sunday
morning associated with secondary vort, pocket of 850 to 500mb rh
>70%, and modest lake instability. However, cloud layer flow is <30
knots and from a westerly direction, so areal coverage downwind of
Lake Ontario will be limited. Highest pops will be acrs northern NY
btwn 06-12z Sunday. Temps wl be seasonably cool Sat night with lows
upper 20s to near 40F, warmest near Lake Champlain, while highs
climb back into the upper 40s to l/m 50s on Sunday, with summits
holding in the 30s. Sunday night fast confluent flow increases as
mid/upper lvl trof tries to dig south, while ridge builds acrs the
SE CONUS. This produces strong 500mb winds of 50 to 80 knots acrs
our fa, while sharpening the north-south moisture and thermal
fields. Latest 00z trends in all the guidance has been for a shift
northward in this gradient, producing stronger forcing and better
moisture acrs our central/southern cwa by 12z Monday. Have bumped
pops into the schc near International Border to likely for
Rutland/Windsor Counties, with sharp north-south gradient
anticipated. Expect additional shifts in the pops/qpf fields as we
head into the weekend, especially if northerly flow develops from
sfc high pres near Hudson Bay and drier air advects southward. Given
thermal profiles some wet snow is likely above 4000 feet late
Sunday Night, as progged 850mb temps hover btwn -1C and 0C.
Coolest temps wl be NEK with lows mid/upper 20s to lower 40s
southern SLV on Sunday Night.
.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 409 AM EDT Friday...Fcst challenge remains pops/qpf for early
week, associated with sharp boundary draped acrs the Mid Atlantic/NE
CONUS. 00z trends in all the guidance has been to place higher 850
to 500mb rh fields further north, along with better fgen forcing
associated with tightening thermal gradient acrs our fa for Monday
into Tues. Have noted GFS/GEM and UKMET in good agreement, while
ECMWF is still the slowest with building precip fields northward
into our cwa. Given the trends and position of sfc high pres near
Hudson Bay instead of building southward into our cwa, I have
included pops into the likely range from central/southern cwa with
chc for northern areas on Monday. These pops are tapered back to chc
for Monday night into Tuesday, but if trends prevail wl need to
increase some more, especially if 00z guidance is correct. A cold,
raw and damp day is likely acrs our cwa Monday, with progged 925mb
to 850mb temps hovering btwn -2C to +2C from north to south acrs our
fa. These values support the idea of snow levels near 4000 ft on
Monday from the northern Dacks into the higher summits of VT, with
several inches possible. Have trimmed back temps and trended toward
the NBM 25% values for Monday/Tues based on northerly winds, clouds
and precip, which support upper 30s/lower 40s to mid/upper 40s,
while summits hold in the 30s. Still some uncertainty on how fast
mid/upper lvl system and associated sfc low pres eject eastward into
the Northern Atlantic for Tues/Weds, with ECMWF/GEM much slower,
while GFS is the fastest. The ECMWF/GEM show deepening and closing
off 7h/5h circulation over SNE, with 996mb low pres over Cape Cod by
12z Weds, while GFS has same idea, but well east of the 40/70
benchmark. The overall pattern has a low predictability especially
when guidance is trying to transition from a fast confluent flow
aloft to more of a blocking/amplifying mid/upper lvl pattern. Based
on this have continued with chc pops for Tues/Weds with temps on the
cooler side of guidance, especially for daily highs. Next large
scale synoptic system looks to approach fa late Thurs into Friday
with additional precip chcs, along with some wind threat. Overall
system evolution and strength wl be better modeled in the days
ahead, so stay tuned.
.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Through 12Z Saturday...A mix of VFR/MVFR/IFR conditions across
the air space with lowering ceilings behind a cold front
currently over the Adirondacks. Some post-frontal gustiness in
the 20 to 25 knot range has been observed at MSS which should
diminish gradually in the next couple of hours. Expect less
gusty winds farther east, but brief gusts to 20 knots will be
possible at BTV in advance of the front through 15Z. Lifting of
low clouds is expected with time behind the front, with return
to VFR ceilings expected at MSS after 19Z but may remain MVFR at
SLK through 06Z.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. Slight chance SHRA.
Sunday: VFR. Slight chance SHRA.
Sunday Night: Mainly VFR, with local MVFR possible. Chance RA.
Monday: Mainly MVFR, with areas VFR possible. Chance RA.
Monday Night: Mainly MVFR, with areas IFR possible. Chance RA,
Tuesday: Mainly IFR, with local MVFR possible. Chance RA.