356
FXUS61 KBUF 262238
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
538 PM EST Tue Nov 26 2024

.SYNOPSIS...
Nuisance lake effect rain and wet snow showers will be found east of
Lakes Erie and Ontario into Wednesday...and while this activity could
result in a few inches of snow across the higher terrain...it will NOT
impact holiday travel heading into Thanksgiving. A weak storm passing
to our south will produce a little light rain and or wet snow for
Thanksgiving Day with any accumulations being limited mainly to the
higher terrain. Colder air pouring over the region through the holiday
weekend will then set the stage for SIGNIFICANT lake effect snow east
of Lakes Erie and Ontario.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
...NO Travel problems through at LEAST Wednesday evening...

A cyclonic flow of relatively cold air will generate some nuisance lake
effect rain and wet snow showers east of both lakes into Wednesday. The
most widespread precipitation will be east of Lake Ontario where
a longer fetch will combine with a little more synoptic moisture
to allow for minor one to 3 inch accumulations across the higher
terrain east of Lake Ontario. Off Lake Erie, cloud tops will be
marginally cold enough to support dendritic snow growth,
yielding only lake effect clouds at times.

A flat zonal flow with high pressure centered just to our south will
provide fair dry weather for the bulk of the area on Wednesday...but
there will still be some lake effect rain and wet snow showers east of
both lakes. Very minor accumulations will be possible...mainly in the
vcnty of the Tug Hill where another inch or so of snow could
accumulate. Temperatures Wednesday will top out in the low to mid 40s.

It may get a little interesting across our region later Wednesday
night...as sfc a wave riding along a stalled frontal boundary over the
Tennessee valley could become organized into an area of low pressure
that will move to the Mid Atlantic region. Guidance has had a lot of
difficulty in resolving this scenario...as some packages suggest more
of a wavy frontal boundary further to the south while others favor the
idea of an organized low that could spread a light accumulating snow
fall as far north as Lake Ontario. While the guidance packages have
come a little closer in agreement...there is still enough uncertainty
as to the northern extent of the pcpn to account for a low confidence
forecast.

That being said...will generally maintain cat to likely pops Wednesday
night with the highest potential for minor snowfall being found across
the western Southern Tier where an inch or two of snow cannot be ruled
out. Given road temperatures...forecast low temperatures and expected
snowfall rates...this should not impact travel for the overnight.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Thanksgiving will feature a storm system passing by to our south,
with precipitation brushing by our region through the day. The lead
shortwave within a closed upper level low will drive this surface
low and its associated moisture from the mid-Appalachians to off the
southern New England coastline through the day.

This event will again be an elevation driven event, with the higher
terrain receiving mainly snow, with an inch or two of accumulation
across the Upper Genesee and Tug Hill region...while lower
elevations will feature more of a rain/snow to plain rain event.
Greatest odds for 4 inches of snow (a continued decreasing
percentage that is now around 45%) is atop the Tug Hill Plateau.
Snow will feature a wetter texture through the day, then taper off
as lighter fluffier snow as cold air is drawn southward behind the
departing surface low.

A lull overnight Thursday, this behind the departing storm, and an
approaching secondary shortwave that will return deeper synoptic
moisture as well as draw colder air southward.

...Lake Effect Snow...

Winter storm watches for heavy lake effect snow remain in place with
this forecast package update.

Late Thursday night through Friday night shortwave trough/axis
around a closed upper level low over southern Canada will deepen 850
hPa temperatures to -9 to -10C over the Lower Great Lakes. Heights
at 850 hPa and 500 hPa are not far from analogs for heavy snow
events for the Chautauqua Ridge and Tug Hill Plateau.

Expect lake snows to develop along the southern Lake Erie shoreline
late Thursday night and early Friday morning as the leading front of
deeper moisture intersects with an aligning lower level flow. This
band will impact Chautauqua and inland towards the ridge through the
day with accumulations of several inches. This band of snow will
push inland towards the Boston Hills/Wyoming Hills through the day.
Marginal temperatures across the lower terrain will allow for a
change over to plain rain showers...along the warm Lake Erie
shoreline and inland across the Lake Plain. As the moisture and
deeper colder air moves eastward, a band of lake snows...possibly
settling in across northern Jefferson County early with just an inch
or two of accumulation.

By Friday night a westerly flow will develop behind the shortwave,
with healthy plumes of lake snows oriented due east of the Lakes. A
half to one foot of accumulation, is likely along the Chautauqua
Ridge, with diminishing amounts farther inland across the Southern
Tier...and east of Lake Ontario a half to one foot of accumulation
is likely over the Tug Hill Plateau. This westerly flow will also
allow for minimal impacts for the Buffalo to Rochester corridor,
with likely breaks in the clouds overnight.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Deep cold cyclonic flow will continue throughout this period as the
axis of upper level troughing slides from near the Ontario/Quebec
border to the Canadian Maritimes and New England...with consensus
850 mb temperatures averaging between -9C and -12C. This environment
will support a potential for significant lake effect snows downwind
of the lakes throughout with the latest suite of guidance continuing
to support the idea of a general westerly flow resulting in the lake
snows primarily targeting the traditional snowbelts east of the lakes
through the weekend. As such...Winter Storm Watches for lake effect
snow remain in effect through Sunday night for southern Erie/Wyoming
and Chautauqua/Cattaraugus counties east of Lake Erie...and
Oswego...Jefferson...and Lewis counties east of Lake Ontario.

The above being said...the approach and passage of hard-to-resolve
subtle shortwave impulses could still lead to some fluctuations in
the low level wind field and consequently band placement during the
weekend...with variations in background moisture and environmental
shear also potentially modulating band intensity and organization at
times. As a case in point...a minority of the guidance (meaning that
the following is a rather LOW confidence scenario) currently
suggests the potential for the lake bands to temporarily migrate as
far north as areas northeast of the lakes sometime between later
Saturday and Sunday morning...though at the same time there are also
suggestions that there may also be some drying and an increase in
shear that would act to limit band organization. The bottom line
here is that at this still-somewhat distant vantage point...there is
still MUCH uncertainty in the precise location and strength of the
bands at any given point in time...which make pinning down residence
times and actual snowfall amounts impossible until such details
(hopefully) come into better focus over the coming days...and as the
event draws closer.

As the axis of the upper trough slides east of our longitude later
Sunday/Sunday night through early next week...the large-scale flow
should tend to become more west-northwesterly to northwesterly...
which would result in the lake snows shifting to areas east-southeast
or southeast of the lakes while also tending to become more multibanded
in nature. This may eventually require the issuance of additional
winter weather headlines for early next week for areas south of
Lake Ontario...as well as possible extensions of headlines for those
portions of the current Watch areas still under the influence of
the lake bands at that time (i.e. Chautauqua/ Cattaraugus counties
off Lake Erie...and Oswego county off Lake Ontario).

Otherwise...locations outside of the main lake effect areas should
be largely dry...with just a few scattered snow showers possible at
times. As for temps...the cold airmass will easily ensure below
normal temperatures throughout this period... with daily highs
averaging in the upper 20s to mid 30s...and nightly lows in the
mid/upper teens to mid 20s.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
While mainly VFR conditons with cigs of 3500-5000 will be found
throughout the bulk of the region this afternoon...MVFR cigs in lake
effect rain and wet snow will be found east of both lakes. Sfc winds
this afternoon will average 20 to 30 knots at most locations.

Tonight and Wednesday...VFR conditions will be found at the larger TAF
sites...while lake effect snow will maintain MVFR weather across parts
of the western Southern Tier (ie. KJHW) and for areas east of Lake
Ontario (but south of KART).

Outlook...

Wednesday night...Deteriorating conditions to MVFR/IFR levels in light
snow late.
Thursday...MVFR/IFR with some wet snow and rain.
Friday through Sunday...VFR/MVFR for most of the TAF sites with
scattered light snow showers. IFR/LIFR in moderately heavy  lake effect
snow east of both lakes.

&&

.MARINE...
...Gale Warnings in Effect...

Cold advection within a deep cyclonic flow will support sustained
westerly winds of 30 knots with frequent gusts of 35 to 40
knots. The resulting gale warning will be in effect through this
evening on Lake Erie and through much of tonight on Lake
Ontario.

Weak high pressure passing by to the south on Wednesday will allow
winds and waves to subside, but small craft advisories will
likely be needed, particularly on Lake Ontario.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Storm Watch from Friday afternoon through Monday
     morning for NYZ006>008.
     Winter Storm Watch from Friday morning through Monday morning
     for NYZ012-019-020-085.
MARINE...Small Craft Advisory until 7 AM EST Wednesday for LEZ020.
         Gale Warning until 10 PM EST this evening for LEZ040-041.
         Small Craft Advisory until 10 PM EST this evening for
         LOZ030.
         Gale Warning until 1 AM EST Wednesday for LOZ042-062.
         Gale Warning until 4 AM EST Wednesday for LOZ043>045-
         063>065.
         Small Craft Advisory until 4 AM EST Wednesday for
         SLZ022-024.

&&

$$

SYNOPSIS...RSH
NEAR TERM...Apffel/RSH
SHORT TERM...Thomas
LONG TERM...JJR
AVIATION...RSH
MARINE...Apffel/RSH/TMA