090
FXUS61 KBUF 250025
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
725 PM EST Sun Nov 24 2024

.SYNOPSIS...
While weak high pressure will promote mainly fair dry weather
through at least lunchtime Monday...a relatively weak storm system
moving through the Lower Great Lakes will generate increasingly
widespread rain showers Monday night. 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 MONDAY NIGHT/...
Other than a few sprinkles across the northern Finger Lakes to the
south shore of Lake Ontario, earlier showers have mostly scattered
out. It remains mostly clouds across much of the area, especially
southeast of the lakes where larger lake fetch and/or upstream lake
connections are allowing for better lake responses for now at least.

A broad low amplitude mid level ridge will approach the region
tonight...while drier air will work in from southern Ontario. This will
all but guarantee fair dry weather tonight with skies at least
partially clearing for all but the western Southern Tier.

The crest of the aforementioned ridge will pass over the forecast area
on Monday...and while this will support partly to mostly skies in the
morning...clouds will be on the increase during the midday and
afternoon. This will especially be the case over the far western
counties where a 25-30kt low level jet will push up and over a
tightening H925-70 baroclinic zone. The cirrus cloud cover that will
steadily increase regionwide will thus lower to a solid deck of strato-
cu over the western counties by mid-late afternoon. In fact...the
lowering cigs will be accompanied by some late day showers...
particularly west of the Genesee county/nr Lake Erie. Otherwise...it
will be a relatively mild day with the mercury topping out within a
degree or two of 50 over the western counties and in the mid 40s east
of Lake Ontario.

Monday night will then be guaranteed to be wet...as a negatively tilted
mid level trough lifting across the Great Lakes will push a sfc low
with its corresponding frontal boundaries through our forecast area.
The initial rainfall will come as a result of isentropic lift ahead and
with the passage of the warm front...but heavier showers will be
associated with deep lift ahead of a fairly strong cold front. Basin
average rainfall of a quarter inch is expected Monday night...although
amounts closer to a half inch will certainly be possible east of Lake
Erie/across much of the Srn Tier.

The other thing to note about the busy weather Monday night is that
temperatures should actually rise several degrees early on as a result
of being thrust into the warm sector behind the initial warm front. As
the cold front plows through though towards daybreak...the non-diurnal
temp trend will continue into the following day.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
General model consensus shows that low pressure will pass by just to
our west-northwest Tuesday, with its trailing cold front crossing
the region. Strong CAA behind the front will then usher in a colder
airmass with temperatures falling over the course of the day. It
will also become quite windy, with gusts possibly up to 40 mph. As
the colder air spills in across the Lower Lakes we will also see
some lake/upslope showers (mainly rain or some wet snow higher
terrain) develop within the westerly flow east of both lakes.

Colder air continuing to filter in Tuesday night will push H850 T`s
down to -7C to -9C across the Lower Lakes. This will be plenty cold
enough to support some measure of showers east and southeast of the
lakes through the night. That being said...the challenge will be the
availability of deep moisture which is lacking in the most recent
(12Z) guidance per BUFKIT sounding profiles. Add to that...EQ levels
are forecast to fall fairly quickly from 9K feet all the way down to
5K feet by Wednesday morning. This will either mute the lake
response or crush it all together. Given latest guidance have reduce
PoPs off lake Erie significantly considering the shorter fetch of
the lake. Off lake Ontario...the longer fetch will help to keep some
lake induce showers going east of the lake overnight.

On Wednesday...a couple of shortwaves working around the mid-level
low and a brief injection of moisture may briefly help to re-
invigorate or keep some residual lake effect showers going east of
the lakes. Otherwise...most locales will see dry weather.  By
Wednesday night...drier air working in again and warming mid-levels
will squash any remaining lake induce showers off the lakes. This
should begin a brief period quite weather before more unsettle
weather returns. More on that in the long term disco.

&&

.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 /01Z MONDAY THROUGH FRIDAY/...
VFR conditions will be found across the majority of the region through
tonight...with the exception of across parts of the Srn Tier (ie. KJHW
and KELZ) where lake enhanced low level moisture will support cigs of
700-1500 feet.

On Monday...VFR weather with gradually lowering cigs will be found at
most TAF sites. Once again...the exception will be across the Srn Tier
where IFR to MVFr cigs will persist.

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 Monday. An earlier, tighter
pressure gradient between this system and a building ridge of high
pressure to the west is starting to relax this evening. Winds and
waves have begun to diminish from west to east this evening as the
high further builds into the region. SCAs remain only on the central
and eastern zones of Lake Ontario.

After a period of gentle to modest breezes and generally offshore
wave action, the next low pressure system will move directly over
the eastern Great Lakes Monday night into Tuesday. This will drive a
cold front through the region, with fresh to strong southwesterly
winds likely into Wednesday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 1 AM EST Monday for LOZ043>045.

&&

$$

SYNOPSIS...RSH
NEAR TERM...RSH
SHORT TERM...AR
LONG TERM...JJR
AVIATION...RSH
MARINE...PP