Current conditions from King Hill
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  Thursday September 20, 2018


NWS Area Forecast Discussion

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FXUS61 KBTV 200549

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

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 are expected for the
upcoming weekend.


As of 133 AM EDT Thursday...Forecast challenge for the next 36
hours is going to be cloud cover as once again dirty high
pressure is settling over the region from the north. Abundant
cloud cover persisted across the CWA today and despite some
peaks of sunshine, temps never made it out of the 60s for most
locations. Looking upstream there`s still a lot of cloud cover
present under the high and models continue to indicate a
subsidence inversion setting up overnight. Forecasting just how
much low level moisture gets trapped below the inversion is
tricky, but based on the latest satellite trends I`m going with
the more pessimistic forecast highlighting more cloud cover than
less, especially across the Adirondacks and eastern Vermont.
The deeper valleys will likely see the most clearing. Temps
tonight will subsequently be difficult, and stayed generally
close to MOS with lows generally in the mid 40s to low 50s.

On Thursday, mid/upper level ridging continues build across the
area and we should see the low level inversion break by mid-
morning allowing skies to scatter out to partly sunny for the
remainder of the day. PoPs are nil and 925mb temps of +11-15C
will support highs close to normal values in the mid 60s to low
70s. Quiet conditions persist through the first half of Thursday
night as well, but after midnight low pressure approaching from
the west will increase cloud cover and southerly winds across
the area. Lows ranging through the 50s will likely occur early
in the night, then gradually rise after midnight with chances
for showers increasing as well with low level moisture and
broad synoptic ascent increasing along the approaching warm


As of 323 PM EDT Wednesday...A low pressure system will track from
the northwestern Great Lakes Region to central Quebec Friday,
pushing a series of fronts through New England that will control the
short term forecast. Plenty of baroclinicity associated with
the early fall system, so should see some impressive temperature
advection over the area Friday. The cyclone`s warm front will
cross the forecast area Thursday night through Friday morning,
spreading some rain through the North Country as it does so.
Very little dynamic support in the upper-levels over our area
(much more impressive further north...), but a broad area of
synoptic-scale ascent from isentropic lift will ensure that most
areas see at least some measurable rain. Given the strength of
the impressive 50+ kt LLJ within the warm-sector of the cyclone,
QPF will vary greatly with terrain. The Saint Lawrence Valley
should see the most precipitation under this setup, while much
of the Champlain Valley will get rain- shadowed, resulting in
significantly lower QPF amounts. Overall for many areas, should
be a higher PoP/lower QPF scenario. Some marginal (<500 J/kg)
elevated CAPE will be present over northern New York, so an
isolated rumble of thunder Friday morning can`t be ruled out.

Winds Friday will be quite gusty from the south/southwest. Strongest
winds will be at highest elevations and in channeled valleys.
Areas of the Saint Lawrence Valley and the Champlain Valley will
see gusts in excess of 25 mph during the afternoon hours as
higher momentum air within the LLJ is mixed to the surface.

High temperatures Friday will be highly variable across the CWA.
Strong warm air advection will allow temperatures to climb into
the low 80s in the Saint Lawrence Valley. The Champlain Valley
should also warm up quite a bit, with highs near or at 80
degrees not out of the realm of possibilities with strong
downsloping southwesterly winds in place. Areas east of the
Green Mountains, however, will be noticeably cooler, topping out
in the upper 60s to low 70s.

Friday night, the system will sweep a strong cold front through
the area, reinvigorating shower activity. Better dynamics aloft
associated with this frontal passage, however best upper
support does lag quite a bit behind the frontal passage. Given
the overnight timing of the frontal passage and the subsequent
lack of much instability, along with the offset of surface
forcing and upper-level support, not overly impressed at this
point with thunderstorm potential. If any thunderstorms are able
to develop along the front however, the strong shear/flow aloft
could support some gusty winds reaching the surface. Once
again, best chances of an isolated thunderstorm or two would be
in the Saint Lawrence Valley, where the earlier timing of the
frontal passage would line up with better instability.


As of 323 PM EDT Wednesday...Large scale pattern shows confluent flow
aloft with general trof across the ne conus as large 1028mb
high pres extents from northern Great Lakes into northern New
England. Overall this pattern supports below normal precip
chances and temps thru early next week. The ECMWF shows a
secondary surge with passage of weak boundary on Sunday, along
with progged 850mb temps dropping to 0c near the international
border. Moisture is very limited, so only expecting clouds
associated with increasing 850 to 500mb rh fields, while best
upper level forcing associated with 5h vort stays north of our
cwa. These northern stream fronts with limited moisture
typically have limited moisture with a wind shift and cooling
low level thermal profiles. Overnight low temps during this time
period will be challenging based on winds with advection and
potential clouds. Have kept very close to guidance, but values
could be 4 to 8 degrees lower if more clearing and lighter winds
develop. Have kept very close to superblend values for days 4
thru 7. This supports highs mainly in the 60s and lowers in the
mid 30s to mid/upper 40s depending upon location, warmest values
near the Lake Champlain. A warming trend with increasingly
moisture arrives on Tues into Weds of next week. Still plenty of
uncertainty on timing of moisture and magnitude of waa.


Through 06Z Friday...Anticyclonic flow around high pressure
over the Canadian Maritimes continues to feed some low-level
moisture into the North Country from the northeast. This
moisture is becoming trapped under a steepening subsidence
inversion, resulting in low stratus clouds loitering over much
of Vermont and into parts of northern New York. Aside from these
stratus clouds, skies are currently clear. These conditions all
combine to make a very tricky overnight aviation forecast, with
a mix of VFR clear skies, MVFR/IFR ceilings under stratus
clouds, and the potential for some localized LIFR conditions if
any of the areas with clear skies see the development of
radiational fog.

Thinking Vermont TAF sites along with KPBG will stay locked under
stratus clouds, with bouncing ceilings generally between 2000
and 4000 ft. Satellite imagery shows a sharp gradient between
stratus clouds east of the northern Adirondacks, and clear skies
along and west of the northern Adirondacks. This puts KMSS and
KSLK in prime conditions for fog development, so expecting some
reduced visibilities within br/fg through the night at these
sites. Lowest visibilities will be at KSLK, which has the
potential to see IFR/LIFR visibilities through around 14Z.

After 14Z, most TAF sites should see conditions to approve to
VFR, however some temporary MVFR ceilings will be possible
throughout the day tomorrow at KMPV and KRUT.

Winds will generally be light and variable through the TAF


Friday: Mainly VFR, with local MVFR possible. Windy with gusts to
35 kt. Chance SHRA, Slight chance TSRA.
Friday Night: Mainly VFR, with areas MVFR possible. Windy with
gusts to 30 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.





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