Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 202349

Area Forecast Discussion
National Weather Service Buffalo NY
649 PM EST Mon Nov 20 2017

High pressure over the Tennessee River Valley will move off the mid
Atlantic Coast tonight. Warmer air will move into the region Tuesday
before the next cold front plows across the area Tuesday night
bringing rain showers. Colder air moving in behind the front could
bring some light mixed precipitation later Tuesday night with some
minor lake effect snow showers Wednesday and Thursday.


Lake effect snow showers have tapered off considerably late this
afternoon with only light activity remaining east of Lake
Ontario. Expect little if any additional snow accumulation this

Southwest flow of drier and milder air will continue to lift
this cloud area northward tonight, as the surface high centered
over the Tennessee River Valley shifts east to the Mid Atlantic
coast. The mainly clear skies over the western counties this
evening will make it into the north country by midnight or
shortly thereafter after. The strength of the warm advection
will support a non-diurnal temperature trend tonight, as our
lows should occur by midnight or so with gradually rising
temperatures through daybreak.

The high pressure situated off to our southeast will allow for a
much milder day with brisk southwest winds ahead of an approaching
cold front. Precipitation associated with the front will likely hold
off until early evening leaving nearly the entire daylight hours
rainfree with a decent amount of sunshine. Trajectories bring our
air in from the Ohio/Tennessee Valleys which would support guidance
high temperatures in the upper 40s to lower 50s.


Tuesday night a cold front will cross the region forced by a
shortwave moving through the lower Great Lakes. Rain showers will
spread across the region along and ahead of the cold front,
eventually switch to and ending as snow late Tuesday night. Any snow
accumulations will be limited to the higher elevation of the
Southern Tier and east of Lake Ontario, and will likely be on the
order of a half inch with a few isolated spots up to a inch.
Precipitation will shut down fairly quickly in the cold air
advection behind the cold front, however some minor lake response
will linger east of Lake Erie and Lake Ontario in Wednesday morning.

High pressure will build across the region Wednesday, which will
help suppress any lingering lake effect Wednesday morning, causing
it to diminish through the day. This will produce a mainly dry day
on Wednesday for Thanksgiving travel, along with near normal

Expect seasonable conditions for Thanksgiving as surface high
pressure to our south shifts eastward. Another shortwave passing
well to our north will drag a weak cold front near the North County
by Thanksgiving evening, and may help elicit a weak lake effect
enhancement off Lake Ontario Thanksgiving night. This will likely
produce some scattered snow showers and light accumulations there.
Otherwise, expect a mainly dry Thanksgiving day across the region.

On Friday...mainly dry and uneventful weather will return as another
narrow ridge of high pressure quickly traverses the region in the
wake of Thursday night`s cold front. As the axis of this ridge
departs to our east...developing warm air advection will help
afternoon highs to largely climb back into the lower 40s south of
Lake Ontario...and into the mid to upper 30s across the North


12Z global models are in agreement with tracking a deep storm system
north of the Great Lakes Friday night and into Central Quebec
Saturday. Southerly flow ahead of this system should result in a non-
diurnal temperature trend Friday night with surface temps rising
ahead of an approaching cold front. Expect that temperature profiles
by the time the cold front arrives will support mainly plain rain on
Saturday with some gusty winds. A strong low level jet and cold
front will combine with a deepening mid-level trough to force this
period of rain showers Saturday as the system passes to our north.
Synoptic moisture is not expected to be anomalously high which
does not support a significant amount of rainfall while the jet
trailing the front would likely keep wind gust sub-advisory level.
Surface highs on Saturday will be pre-frontal with a model consensus
pointing toward mid to upper 40s.

A trailing blast of arctic air behind the cold front should support
a good chance of some upslope and lake effect snow showers Sunday
into Monday. 850mb temps are forecast at this time to dip close to
-15C on Sunday which would support some extreme lake induced
instability and lake induced equilibrium levels rising above 10kft.
Northwest flow would steer lake effect snow bands and lighter
upslope snow showers to the southeast of the lakes with what appears
to be enough synoptic moisture to support a decent lake effect
event. With this still being 6-7 days away have limited POPs to
chance range but this will be something to watch closely especially
for those traveling back home after Thanksgiving. Surface
temperatures will run well below normal with the forecasted blast of
arctic air. Highs Sunday and Monday will likely remain below or just
at freezing.


Expect widespread VFR conditions tonight and Tuesday. The main
concern will be LLWS due to increasing winds aloft which will
not mix to the surface overnight. Winds at 2k ft will increase
to around 45kts after 03Z. LLWS will subside when winds mix to
the surface more readily during the day Tuesday, resulting in
gusty surface winds in some spots.


Tuesday night...Mainly VFR, lowering late.
Wednesday...Rain and snow showers with a chance of MVFR/IFR.
Thursday...VFR, but MVFR in lake effect -SHSN E of the lakes.
Friday and Saturday...Mainly VFR.


Fresh to strong southwesterlies will continue across the lower Great
Lakes through Tuesday, before a cold front moves through Tuesday
night, turning the winds out of the northwest. Moderate to fresh
northwesterlies then will continue through the mid week period.
While the small craft advisories will continue through Tuesday on
the Niagara River and Buffalo harbor, the headiness will be extended
through Wednesday for the Lake Erie and Lake Ontario nearshores.
Conditions may briefly improves Thursday as the graident relaxes,
but winds and waves will again increase toward the weekend ahead of
the next approaching low from central Canada.


MARINE...Small Craft Advisory until 6 PM EST Tuesday for LEZ020.
         Small Craft Advisory until 1 PM EST Wednesday for LEZ040-
         Small Craft Advisory until 6 PM EST Tuesday for
         Small Craft Advisory until 7 PM EST Wednesday for



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