Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 260019

Area Forecast Discussion
National Weather Service Burlington VT
819 PM EDT Tue Sep 25 2018

A moist southerly low-level flow will remain in place across
the North Country tonight into Wednesday. Low clouds with
periods of showers and patchy drizzle are generally expected
tonight, with temperatures slowly rising into the upper 50s to
lower 60s. A strong cold front will approach from southeastern
Ontario and the Great Lakes region on Wednesday. Will see breezy
conditions areawide, with gusts of 30 to 40 mph possible in the
Champlain Valley. During the mid afternoon and evening hours, a
band of showers and embedded thunderstorms are expected as the
cold front crosses northern New York and Vermont. Some
thunderstorms may contain locally damaging winds, along with
brief heavy downpours. High pressure returns with dry conditions
and seasonable temperatures for Thursday and Friday.


As of 803 PM EDT Tuesday...Only have a few updates to the
forecast this evening largely to drop back the chances for
rain showers from chance to slight chance. The radar is largely
shower much of the North Country is quiet through the rest of
the overnight with a few areas of drizzle possible mainly in the
higher terrain. There`s another weak shortwave ahead of the main
cold front that could squeak into the Saint Lawrence Valley this
evening and produce some light showers but we`ll have to see if
it holds together.

Previous discussion...Near-term wx conditions remain active,
culminating in possible thunderstorms with locally damaging
winds mid-late Wednesday afternoon into Wednesday evening as
strong cold front crosses the region.

Best 850-700mb warm advection and associated steady
precipitation is shifting ewd across central/ern VT, and will
generally move east of the CT River by early this evening.
Rainfall amts with the warm front ranged from 0.25-0.35" across
much of nrn NY and VT so far today, with heavier totals across
the southern Green Mtns of 0.5-1.0". For tonight, will remain
embedded in a moist southerly low level flow, with surface winds
around 10-15 mph. Will see persistent low stratus with patchy
drizzle. Looking upstream, next shortwave trough in swly
850-700mb flow regime across swrn NY and wrn PA will cross our
region during the late evening and overnight hours. Maintained
30-60% for rain showers associated with this feature, but
rainfall will not be as persistent as it was earlier today.
Overnight temperatures and dewpoints will generally slowly climb
reaching the lower 60s in most areas before daybreak.

Interesting wx day Wednesday with building sfc-850mb theta-E
ridge in meridional flow regime. Will see continued moderately
strong S-SW gradient winds. In the Champlain Valley, channeled
flow will yield sustained winds 15-25 mph with gusts 30-40 mph
at times during the morning and afternoon hrs Wednesday.

Main question will be potential for convective storms as cold
front approaches from sern Ontario during the aftn hrs, reaching
the St. Lawrence Valley around 19Z, and the Champlain Valley
around 21Z. Per BTV-4km WRF and NAM-Nest, potential exists for
narrow frontal rain band with strong convergence and strong
deep-layer forcing. The sfc-6km bulk shear is also strong at
50-60kts. Appears BINOVC in advance of the cold front will be
limited, and with moist adiabatic lapse rates, max SBCAPE should
be limited to 800-1200 J/kg. However, with temps in the mid 70s
and dewpoints in the mid-upr 60s, should still be sufficient
instability for some lightning potential based on model fcst
soundings. Also, with strong wind fields in place, will need to
monitor for possible strong convective elements in strongly
sheared environment. If storms can become organized with LEWP,
would be concerned for gusts to 60 mph with some of the bowing
elements. We`ll continue to monitor this potential for the
aftn/early eve on Wednesday.

Thereafter, cold front sweeps quickly thru the region with NWLY
winds 15-25 mph following the front. Appears we`ll see partial
clearing from west-east during the overnight hrs, and especially
after midnight. May see a few lingering showers across the mtns
and central/ern VT thru midnight. Lows Wednesday night mainly in
the upr 40s to lower 50s, with dewpoints falling into the upr
40s to lower 50s.


As of 300 PM EDT Tuesday...High pressure will be quick to build across
the region Thursday morning which will abruptly put an end to
rainfall across the North Country. A few days ago it looked like
precipitation may continue to upslope across the higher terrain
of the Green and Adirondack Mountains but given the amount of
dry air and southwesterly flow aloft, the chances look very
unlikely at the moment. Thursday should be a very beautiful fall
day across the region with mostly sunny skies and near normal
high temperatures (upper 50s to mid 60s) expected. Winds will
also be diminishing through the day after multiple gusty days
observed on Tuesday and Wednesday as the pressure gradient
relaxes and upper level support diminishes. Thursday night will
be near normal (lower 40s to lower 50s) as some clouds begin to
move in overnight. There is the potential for fog with recent
rainfall and calm winds Thursday night but the details for that
will be worked out in the coming days.


As of 300 PM EDT Tuesday...Friday morning could be a little showery
across southern Vermont as a decent shortwave traverses the
southwesterly flow aloft. This disturbance will quickly lift
north and eastward into Maine by late morning allowing for
rainfall chances to diminish once again. However, by Friday
afternoon, another cold front will begin to approach northern
New York from the northwest. With moisture lacking following the
passage of the cold front Wednesday and the fact that any upper
level support will likely be north of the international border,
rain chances will be rather low as the cold front pushes
through. This front will largely act as a reinforcing shot of
colder air heading into the weekend rather than a significant
rain maker. Temperatures through the weekend will max out in the
mid 50s to lower 60s with overnight lows in the lower 30s to
mid 40s with Saturday night currently looking to be the coldest
of the two nights.

The pattern becomes more complicated come Monday as a surge of
moisture begins to rotate around the upper level high pressure
centered over the southeastern United States. This will pass through
the North Country sometime between late Monday and late Tuesday as a
warm front which will warm temperatures slightly Monday into Tuesday
but still keeping temperatures near their climatological normals.
Models are actually in very good agreement with the system and
placement sans timing which gives us good confidence in the 66 to 7
day timeframe that we could see another widespread quarter to three
quarters of an inch rainfall sometime late Monday through


Through 18Z Wednesday...Expect generally MVFR/VFR ceilings
through the rest of the overnight with a brief period of IFR in
low stratus at BTV. The may be some patchy drizzle overnights
as were in the warm sector between a warm and a cold front.
A modest low level jet will continue over the Green this evening
leading to some LLWS mainly impacting MPV. Expect MVFR/VFR
ceilings to continue through mid day on Wednesday as a line of
showers will sweep across the North Country with some potential
for strong gusty winds. Ahead of the front we`ll see the
gradient winds significant increase with 20-30kts possible out
of the south. Wind shift associated with the frontal system
should occur between 18-20z for SLK/MSS and 20-22z for the
Champlain Valley and east.


Wednesday Night: Mainly VFR, with local MVFR possible. Chance
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: VFR. Slight chance SHRA.
Friday Night: VFR. Chance SHRA.
Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.
Saturday Night: VFR. Slight chance SHRA.
Sunday: Mainly VFR, with local MVFR possible. Slight chance SHRA.


The Lake Wind Advisory will be extended through tonight, and
will likely need to be continued through the day Wednesday.
South winds will remain in the 20-30 kt range, with waves
generally 3 to 5 feet through tonight, and possibly 4 to 6 feet
across the northern half of the broad portion of Lake Champlain
during the daylight hours Wednesday. A cold front will bring
possible thunderstorms and high winds late Wednesday afternoon,
followed by a wind shift to northwesterly at 15-25kt Wednesday




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