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  Thursday September 20, 2018

 

NWS Area Forecast Discussion


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364
FXUS61 KBTV 201129
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
729 AM EDT Thu Sep 20 2018

.SYNOPSIS...
High pressure to our north and east will provide another quiet
day today for the North Country. The weather becomes more active
tonight, however, as a Canadian low to our northwest pushes a
series of fronts through the forecast area Friday and Friday
night. Expect windy conditions and some showers through the day
Friday, with a potential for a few thunderstorms Friday night.
Behind the system, cooler and drier weather is expected for the
upcoming weekend.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 544 AM EDT Thursday...Tweaked hourly temperature and
dewpoint forecast to match observations, otherwise no other
updates needed. Satellite imagery shows low stratus persisting
over much of the forecast area, while high clouds begin to move
in to northern NY from the west ahead of an approaching warm
front.

Previous discussion...Stout subsidence inversion over much
of New England is trapping low-level moisture near the surface,
result in widespread low stratus clouds that will persist
through this morning. The exception to this is the northwestern
portion of the forecast area, which is further removed from the
influence of the Canadian Maritime high, and seeing clear skies
and some patchy fog development early this morning. Forecasting
just how long the stratus clouds will lurk around today remains
a challenge, but given the rising heights aloft, should see
enough sun today to mix out the low-levels and break out of the
clouds by the early afternoon in most locations. High
temperatures today will again be in the 60s. Given the warm
start to September, this may feel relatively chilly, but today`s
high temperatures will actually be near or still slightly above
climatological normals for late September.

Through the day, high clouds will spread over the area from
west to east in advance of an approaching warm front. The
passage of the warm front will occur during the overnight hours
tonight, setting up fairly impressive warm air advection
overnight. Low temperatures in northern New York and the
Champlain Valley will occur shortly after midnight tonight, then
temperatures will stay near constant or gradually rise through
the remainder of the night. East of the Green Mountains in
Vermont, temperatures will exhibit a more typical diurnal trend
as the warmer air won`t arrive till the day time hours. A broad
area of isentropic ascent within the warm air advection regime
will support some shower activity over the CWA tonight through
Friday morning, however lack of upper support and a strong (50+
kt) southwesterly LLJ will limit QPF amounts in many areas.
Models continue to indicate the best chances for measurable
precipitation over the Saint Lawrence Valley and along the
US/Canadian border, while the Champlain Valley will likely be
downsloped and see less precipitation. Overall, forecasting a
tenth to a quarter of an inch of QPF Friday morning through
Friday afternoon in northern NY and far northern VT, while the
Champlain Valley, central, and southern VT will only see a few
hundredths of precipitation associated with the warm front
passage.

Winds will be quite gusty Friday as strong flow aloft sets up
over the CWA.  Southwesterly/southerly winds will pick up through
the morning, peaking with gusts between 25 and 40 mph during
the afternoon hours as mixing within the lower-levels
transports higher momentum air from aloft down to the surface.
The strong warm air advection will limit the depth of the PBL
during the afternoon, so not expecting the full brunt of the LLJ
to mix to the surface. Not expecting to reach wind advisory
criteria for this reason, but nonetheless, a windy day can be
expected. Strongest winds will be along the higher peaks along
with channeled valleys, including the Saint Lawrence and
Champlain Valleys.

High temperatures Friday will be highly varied across the
forecast area. Warmest temperatures will be in the Saint
Lawrence Valley, where strong waa will support highs reaching
the low to mid 80s. The Champlain Valley will also see well
above normal temperatures, topping out in the mid to upper 70s.
Some degree of adiabatic warming within the strong downsloping
winds should be expected east of the northern Adirondacks, so
have locally nudged temperatures up a degree or two in the
northern Champlain Valley.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
As of 323 AM EDT Thursday...Another round of showers is expected
Friday night as a strong cold front crosses the region. Conditions
not looking that favorable for any convection; frontal passage will
mainly be after dark and the surface/upper support will not be
coincident. However, shear will be ample with a strong low-level jet
resulting in 0-6km shear values of 50+ kt. Hence if any
thunderstorms are able to develop along the front, they will be
capable of producing gusty winds. Our northern NY zones will have
the best chances of seeing any convection, particularly the St
Lawrence Valley as the frontal passage will occur closer to daytime
heating there. Gusty winds will continue both ahead and behind the
front, first from the south, then turning to the west and northwest
post-front. Drier air will quickly work into the region behind the
front and anticipate showers will be ending by daybreak Saturday.
North to northwest winds will remain brisk through at least the
morning hours, making for a fall-like feel, though afternoon
sunshine will help. Highs will be in the upper 50s to lower 60s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 323 AM EDT Thursday...High pressure will dominate the region`s
weather through the first part of next week. A secondary push of
colder air will filter in Sunday, but this frontal passage looks to
be dry as available moisture will be limited. Temperatures will be
near to below normal during this time frame, with highs in the upper
50s to lower 60s and lows in the mid 30s to lower 40s; some patchy
frost will be possible in the usual cold spots in the Northeast
Kingdom and Adirondacks where temperatures will flirt with the
freezing mark. The high will shift to our east Tuesday as a trough
digs to our west, placing us under deep southwest flow. Hence expect
a warming trend with increasing moisture for mid week. Precipitation
chances will return Tuesday and Wednesday as much of the long-range
guidance indicates a frontal passage sometime during this time
frame. Have capped PoPs at high chance/low likely owing to
uncertainty in arrival of deeper moisture and timing of the front.

&&

.AVIATION /11Z THURSDAY THROUGH MONDAY/...
Through 12Z Friday...Early morning fog has lifted in most areas,
however stratus clouds with ceilings between 2000 ft and 4500
ft persist throughout the forecast area. Expecting all TAF sites to
see ceilings rise to above 3000 ft by 14Z, with VFR conditions
continuing through the day. High clouds in advance of an
approaching warm front will thicken through the evening. As the
warm front moves through overnight, some scattered showers will
develop, mainly after 06Z. Flight conditions will deteriorate
after 06Z as ceilings lower to below 1000 to 3000 ft throughout
the forecast area.

Light and variable winds today will become southerly 10-15 kts
after 06Z.

Outlook...

Friday: Mainly VFR, with local MVFR possible. Windy with gusts to
30 kt. Chance SHRA.
Friday Night: Mainly VFR, with areas MVFR possible. Windy with
gusts to 35 kt. Chance SHRA.
Saturday: Mainly VFR, with local MVFR possible. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. NO SIG WX.
Sunday Night: VFR. NO SIG WX.
Monday: VFR. NO SIG WX.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.

&&

$$
SYNOPSIS...RSD
NEAR TERM...RSD
SHORT TERM...Hastings
LONG TERM...Hastings
AVIATION...RSD



 
 
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