Current conditions from King Hill
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  Thursday September 20, 2018


NWS Area Forecast Discussion

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FXUS61 KBTV 192336

Area Forecast Discussion
National Weather Service Burlington VT
736 PM EDT Wed Sep 19 2018

High pressure settling southward into the region will provide
dry conditions, occasional cloudiness and near normal
temperatures to the region through Thursday. A strong low
pressure system tracking northeast of the forecast area will
bring a windy conditions Thursday night into Friday, along with
periods of showers and possibly thunderstorms Friday night as
the associated cold front pushes through. Behind this front
cooler and drier weather are expected for the upcoming weekend.


As of 733 PM EDT Wednesday...Still a really tough call on the
cloud cover here tonight, which leads to challenge of fog
formation or not. Did not make any large changes for the 730 pm
update. Previous discussion follows.

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 18Z Thursday...Very tricky aviation forecast for the
next 24 hours as despite high pressure building overhead, an
abundance of low level moisture and possible developing
inversion overnight will make for variable cloud cover with the
potential for lots of MVFR/IFR. Highest confidence in the
forecast is this afternoon and early evening where mainly VFR
is expected with current areas of MVFR ceilings lifting to VFR
over the next couple of hours. VFR persists through sunset
before the low level inversion begins to develop trapping low
level moisture at the surface. Beyond 02Z confidence is low as
to the expected ceiling height where currently the forecast is
more pessimistic with ceilings lowering to a mix of VFR to IFR
with areas of FG/BR possible. If low flight categories do
develop, they`ll likely last into mid-morning Thursday before
lifting to VFR by 16-18Z. In regard to winds, should be
generally north to northeast 5-10kts this afternoon, and become
light and variable overnight.


Thursday Night: VFR. Chance SHRA.
Friday: Mainly VFR, with areas MVFR possible. Chance SHRA, Slight
chance TSRA.
Friday Night: Mainly VFR, with areas MVFR possible. Likely 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. Slight chance SHRA.
Monday: VFR. Slight chance SHRA.




NEAR TERM...Lahiff/Neiles

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