243
FXUS61 KBUF 250845
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
345 AM EST Mon Nov 25 2024

.SYNOPSIS...
While weak high pressure will promote mainly fair dry weather
through at least lunchtime today, a relatively weak storm system
moving through the Lower Great Lakes will generate increasingly
widespread rain showers tonight. The rain could mix with a bit of
wet snow east of Lake Ontario. Colder air in the wake of this system
will then promote some lake effect rain and snow east of both lakes
for Tuesday and Tuesday night with some accumulation expected east
of Lake Ontario. While some nuisance rain or wet snow showers will
be possible for the big travel day on Wednesday...there is the
chance for unsettled weather on Thanksgiving and then potentially
SIGNIFICANT lake snows east of the lakes for Thanksgiving weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
A ridge of surface high pressure directly over the region this
morning will shift east to New England through the day today.
Generally quiet weather can be expected through much of the day with
some patchy lake effect and upslope cloud cover early on as residual
moisture remains trapped under the subsidence inversion. This lower
cloud cover should continue to slowly scatter out through the
morning as temps aloft warm. Sfc temps will be seasonably chilly to
start the day, especially where skies have stayed clear for longer
east of Lake Ontario.

Upstream WV satellite imagery this morning indicates one fairly
compact shortwave near the Saskatchewan/Manitoba border and a
secondary mid-level disturbance over the Upper Midwest. These two
features will slowly combine to drive an increasingly negatively
tilted trough across the Great Lakes tonight, with the corresponding
sfc low tracking northeast from southern Michigan to southern
Ontario. A 30kt LLJ within the warm sector of this system will begin
nosing into the eastern Great Lakes by the mid to late afternoon,
leading to an initial increase in cirrus followed by lower mid cloud
cover. There could be a few showers accompanying this thicker deck
of cloud cover, though widespread rain will arrive as the system`s
cold front draws closer tonight. Rain could initially start off as
some wet snow east of Lake Ontario with colder boundary layer temps
to start, while the steadier precipitation should begin to wane in
coverage across far western NY very late in the night as a
drier airmass advects into the region behind the front. Basin
averaged rainfall amounts of about 0.25" are expected, though
totals closer to a half inch will be possible in the western
Southern Tier and southeast of Lake Ontario.

Warmer air surging northward ahead of the front will cause a non-
diurnal trend across the region tonight. Temperatures will likely
hit their lows early on before rising several degrees overnight,
only bottoming out in the low to mid 40s across western NY with
low 30s east of Lake Ontario.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
Low pressure will track just to the north of the region Tuesday as
its associated cold front finishes crossing the area. A boost in
cold air advection behind the frontal passage will cause
temperatures to slowly fall off during the day. Elevated mixing
heights within the cold advection will bring windy conditions with
gusts up to 40 mph possible, with the strongest winds focused closer
to the Lake Erie and Lake Ontario. As the colder air spills in
across the lower Great Lakes we will see some lake/upslope showers
(mainly rain or some wet snow higher terrain) develop within the
westerly flow east of both lakes.

Colder air within a westerly flow will continuing to filter in
Tuesday night with 850 mb temperatures down to around -8C. This will
be plenty cold enough to support lake induced precipitation east of
the lakes. Lower elevations probably stay with mixed showers, but
high terrain will change over to snow. Lowering inversion heights
off Lake Erie should limit the potential for accumulation. Better
moisture and longer fetch will bring a better environment east of
Lake Ontario, with the Tug Hill potentially seeing a few to several
inches of snow through Wednesday morning.

Westerly flow will remain into Wednesday morning, with lake effect
showers continuing east of the lakes. A backing flow will take what
is left of the lake effect showers and shift the activity northward
through the day and into the evening.

Low pressure tracking from the Tennessee into the Ohio Valley later
Wednesday night could bring a period of light rain and snow, but
this time period remains uncertain as the GFS and CMC keep the
northern shield of the precipitation associated with the advancing
low south of the region, while the more consistent Euro is farther
north with the associated area of precipitation.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
While there remains good agreement on the next surface cyclone
taking shape across the southern Plains states by sometime on
Wednesday...there also remains considerable uncertainty on the
evolution of this system through the first couple days of this
period. These appear to be the result in differences in the degree
of phasing that occur between the shortwave initially responsible
for the development of the surface low...and the larger-scale upper
level trough over eastern Canada and the northern CONUS. Of the
three main operational models...the ECMWF continues to insist on a
greater degree of phasing and subsequently a more northerly overall
track to the low (albeit a bit further south than in its previous
run)...with the center passing along the Mason-Dixon line during
Thanksgiving Day...then ejecting northeastward along the New England
coast Thursday night. Were the low to take such a track...a fairly
widespread accumulating snowfall would be likely from late in the
Short Term period through the Thanksgiving holiday and into Thursday
night. Meanwhile...the GEM and GFS remain just as equally insistent
on a much more southerly track which would keep the precip from this
system either largely or totally south of our area...with just some
limited lake effect possible to the lee of the lakes. Given the
rather large changes seen in the guidance suite for this timeframe
over the past 48 hours (from largely dry two days ago to much wetter
yesterday...and then to last night`s and today`s disparate
solutions)...the resulting forecast uncertainty requires keeping
PoPs for the Thanksgiving holiday confined to the chance range for
now.

What does appear much more certain is that once this system passes
by our longitude...a cyclonic flow of much colder air will
overspread our region from Friday through the upcoming weekend and
beyond...just in time for the start of December and meteorological
winter. This will not only ensure that temperatures will fall to
below normal levels (with highs struggling to get much above the mid
20s to mid 30s next weekend)...but should also support potentially
significant accumulating lake snows downwind of the lakes. At this
VERY early juncture...the pattern appears to support a general
westerly to northwesterly flow that would tend to favor areas east
and southeast of the lakes...though it must be emphasized that the
inherent uncertainties in wind direction and consequently band
placement this far out make pinpointing more precise locations/
amounts a futile exercise. Needless to say...this time frame will
require close monitoring as we move through the upcoming week.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
Mainly VFR weather will continue overnight as surface high pressure
moves over the region. There remains some patchy lake induced cloud
cover with cigs 2.5-3.5kft south of Lake Ontario as higher cloud
cover gradually thicken from the west. MVFR cigs with pockets of IFR
will be more commonplace across the higher terrain of the Southern
Tier (KJHW to KELZ).

Cigs will gradually lower from VFR to MVFR from west to east Monday
afternoon ahead of an approaching low pressure system. There is a
low-end chance for showers before 21z, though more widespread rain
will arrive at the western terminals (KIAG/KBUF/KJHW) closer to 00z
Tuesday before spreading eastward. MVFR vsbys will be possible
within this area of rain while cigs continue lowering to IFR near
the end of the 06z TAF cycle.

Outlook...

Monday night...MVFR to IFR cigs in widespread rain showers.
Tuesday...Mainly MVFR conditions with rain and snow showers.
Wednesday...VFR weather for most areas except MVFR conditions in lake
effect  rain and snow showers east of Lake Ontario.
Thursday and Friday....MVFR conditions in mixed rain and snow.

&&

.MARINE...
A large low pressure system over the Canadian Maritimes will slowly
weaken and drift east into the Atlantic today. The pressure gradient
over the eastern Great Lakes has relaxed as surface high pressure
moves over the region, thus allowing winds and waves to diminish
below SCA thresholds.

After a period of gentle to modest breezes and generally offshore
wave action, the next low pressure system will move just north
of the eastern Great Lakes tonight into Tuesday. This will
drive a cold front through the region, with fresh to strong
southwesterly winds lasting into Wednesday. Gale force winds
will be possible on both lakes Tuesday morning into Tuesday
night.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Gale Watch from Tuesday morning through Tuesday evening for
         LEZ040-041.
         Gale Watch from Tuesday morning through late Tuesday
         night for LOZ042-062.
         Gale Watch from Tuesday morning through late Tuesday night
         for LOZ043>045-063>065.

&&

$$

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