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  Thursday September 20, 2018

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 190725
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
325 AM EDT Wed Sep 19 2018

.SYNOPSIS...
Morning clouds will give way to partial sunshine this afternoon
as high pressure and it`s cooler airmass settle south across
the region. Temperatures gradually warm by Thursday into Friday
before a strong cold front and associated showers push through
the area Friday evening. Behind this front cooler and drier
weather are expected for the upcoming weekend.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 325 AM EDT Wednesday...Variable cloud cover continues to
advect slowly south into the forecast area this morning behind a
departing early fall cold front. A secondary, back door front
is also pushing southwestward across eastern New England and
will reach the CT River Valley by sunrise with additional clouds
and perhaps spotty drizzle under a more maritime airmass. The
forecast challenge today will be how soon these clouds mix out
and the degree to which boundary layer warming governs
temperature maxima. I feel the NAM output continues to
exaggerate the strength of the frontal inversion and it`s much
cloudier/cooler thermal profiles are too pessimistic, especially
west of the Greens. Time will tell but for now have leaned more
toward a model-blended solution showing skies trending partly
sunny by afternoon in most areas with temperatures ranging
through the mid and upper 60s under modest boundary layer
mixing. It is September, not December.

By tonight weak surface high pressure bridges into the area with
large scale height rises aloft. Winds will be light north to
northeasterly, with occasional clouds being most prevalent across
eastern VT counties under lingering maritime airmass affects. Again,
some spotty drizzle may be possible in these areas. Low temperatures
a blend of mainly bias-corrected guidance ranging through the 40s to
around 50, though locally milder near Lake Champlain.

By Thursday surface to mid level ridging continues across the area
with light north to northeasterly winds tending to veer more
east/southeasterly toward evening in advance of our next system.
Partly sunny skies should be the rule with some broad increase in
mid to upper level cloud cover across northern NY toward day`s end.
Temperatures to moderate slightly with max values mainly from the
mid 60s to lower 70s.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 300 AM 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.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 300 AM EDT Wednesday...Weather turns more benign, but
noticeably cooler, this weekend as we settle into fall-like
conditions behind the cold front. Highs Saturday and Sunday will
only be in the low to mid 60s. Saturday night will be the
coolest night in quite some time with temperatures in the mid
30s to mid 40s expected. Areas of the Northeast Kingdom and
northern Adirondacks will be the coldest, and should see a frost
or possibly even a freeze Saturday night.

Monday night, high pressure will shift offshore and return southerly
flow will advect in some warmer air. Temperatures will
gradually climb back towards seasonal values towards the middle
of the week. The next chance of precipitation looks to be in the
Tuesday/Wednesday time-frame as another low tracks
northeastward through Canada, sending a warm front through the
northeastern US.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
Through 06Z Thursday...Widespread IFR/MVFR cigs expected
through the 12-14Z time frame as post-frontal low stratus
settles slowly south and west across the region. Some patchy
drizzle possible with higher terrain obscured. Only exception
will be KPBG where mainly VFR is expected. After 15Z cigs lift
to VFR at all terminals and trend SCT from 035-040 over time.
Winds generally north to northeasterly 5-10 kts through the
forecast period.

Outlook...

Thursday: VFR. Slight chance SHRA, Patchy BR.
Thursday Night: Mainly VFR, with local MVFR possible. Likely
SHRA.
Friday: Mainly MVFR, with local VFR possible. Likely SHRA.
Friday Night: Mainly MVFR, with areas VFR possible. Likely SHRA.
Saturday: Mainly VFR, with local MVFR possible. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. NO SIG WX.

&&

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

&&

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


 
 
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