623
FXUS61 KBUF 191452
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
952 AM EST Sun Jan 19 2025

.SYNOPSIS...
An arctic airmass will settle across the eastern Great Lakes
region today through early next week. The coldest air in more
than five years will build over the region Monday through
Wednesday and this will result in dangerously low wind chills
regionwide, along with accumulating lake snows east and
northeast of the lakes.

&&

.NEAR TERM /THROUGH TONIGHT/...
Regional radar shows light echos amounting to light snow showers
and flurries across western New York this morning. An arctic
airmass will settle across the eastern Great Lakes region
through tonight. Cold air advection will continue with 850 mb
temperatures falling to -18C by late tonight. This will result
in temperatures not rising much today, with highs in the upper
teens to lower 20s. There is only a shallow layer of moisture
this morning which will keep clouds and flurries around through
late morning or so. A coastal low will develop off the Mid-
Atlantic coast today and moisture will increase from the south
which may lead to a 3-6hr period of very light snowfall across
western NY this afternoon.

As the coastal low pulls away to our east, the boundary layer flow
will come around to the west and lake effect snow showers will move
onshore tonight. Forecast guidance is in good agreement that a lake
aggregate trough will develop on the Lakes tonight. Off Lake
Ontario...Hi-res guidance depicts a mesolow developing on Lake
Ontario which will excite lake snows along this boundary.
Accumulating snow is expected to move onto the southern shore of
Lake Ontario with 2-4" possible from Niagara county to Wayne county.
Off Lake Erie... westerly winds will develop multi-bands of lake
effect snow across the western Southern Tier and into southern Erie
and Wyoming counties. Accumulating snows of 1-3" are possible late
tonight with localized higher amounts along the Chautauqua Ridge.
Elsewhere, snow showers are possible as a shortwave trough moves
across the region. Minor accumulations of 1-2" are possible. Lows
will fall to the single digits across western NY to the minus single
digits east of Lake Ontario.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
...FRIGID COLD WITH SIGNIFICANT LAKE EFFECT SNOWS EXPECTED...

During this period the axis of deep upper level troughing will
slowly make its way from the Plains States to New England...with its
attendant pool of arctic air crossing our region in the process.
This will lead to bone-chilling cold as 850 mb temps of around
-20C at the start of Monday fall to as low as -25C or so by Tuesday
and Tuesday night. This will result in high temperatures struggling
to get much above the upper single digits to mid teens Monday...and
then the 5 to 15 above zero range on Tuesday. Meanwhile lows will
fall to the 5 below to 5 above zero range Monday night...and to the
negative single digits in areas away from the lakeshores Tuesday
night. Coupled with expected winds...this will result in apparent
temperatures dipping into the -15 to -25 range at times from later
Monday through Tuesday night...which will eventually necessitate the
issuance of some Cold Weather Advisories.

The bitterly cold airmass will also allow significant lake snows to
develop east of the lakes Monday into Monday night as the low level
flow backs to westerly/west-southwesterly...and as lake induced
equilibrium levels rapidly climb to between 10 and 12 kft over Lake
Erie...and to around 13 kft off Lake Ontario. This general
environment will then remain in place through Tuesday and into
Tuesday evening...before approaching low level ridging begins
introducing drier air and lowering lake-induced EQLs through the
remainder of Tuesday night. This will result in the lake bands
weakening while drifting back southward again Tuesday night as the
low level flow veers a bit more westerly with the approach/passage
of the main upper level trough axis.

While the overall setup is not perfect as the best dendritic snow
growth zone will lie within the lowest couple thousand feet AGL and
below the region of best lift/richest moisture (a factor that could
hold back snowfall ratios/rates somewhat)...the otherwise favorable
thermodynamic environment and long fetch across the lakes should
still be supportive of significant lake effect snows...and with this
in mind the Winter Storm Watches have been upgraded to Lake Effect
Snow Warnings as outlined below.

Digging a bit further into the details...

Off Lake Erie...light to moderate lake snows east of the lake (from
Chautauqua/Cattaraugus counties into southernmost Erie and SW
Wyoming counties) at the start of the Monday will consolidate and
become better organized while lifting northward through the day as
the low level flow backs to about 260 degrees...with the band
eventually spreading across the Buffalo southtowns/southern Genesee
county during Monday afternoon. The lake snows will then remain in
this general vicinity (extending from far northern portions of the
Southern Tier to the Buffalo southtowns and southern Genesee county)
through Tuesday with some subtle north-south oscillations possible
at times...before slipping back southward across southern
Erie/Wyoming counties and deeper into the Southern Tier Tuesday
night as winds veer more westerly again.

Snowfall totals through this period will be heavily dependent upon
the exact orientation of the low level flow and its influence on
band placement and residence time...with some uncertainty still
noted with this in the latest short term guidance. Of note...the
Canadian GEM is furthest north and brings the band directly across
the Buffalo area Monday night into Tuesday...however this model is a
bit of an northern outlier compared to the other guidance...and has
also been so with some other events so far this winter season...
during which it also has turned out to be a bit too far north with
its band positioning. With this in mind...with this forecast have
aimed more toward a band position that`s in between those depicted
by the NAM/GFS and GEM. Based on this...snowfall totals currently
look to range from between 1 to 2 feet from northern portions of
Chautauqua/Cattaraugus counties northeastward across Southern Erie
county...to as much as 8 to 16 inches from south Buffalo and the
Buffalo Southtowns eastward into southern Genesee County.

Off Lake Ontario...expect a broader swath of light to moderate lake
effect snow along/inland of much south shore of the lake at the
start of Monday morning...attendant to a lake-aggregate thermal
trough axis and one or more mesolows rippling eastward along this
boundary. As we push through Monday...all this will gradually shift
eastward to Oswego county while consolidating into a single band as
winds gradually back to more westerly...before shifting further
north to the northern Tug Hill region and intensifying further
Monday night as it aligns with the long axis of the lake. The heart
of the band may then shift a little further north and closer to
(though likely remaining just south of Watertown) on Tuesday...
before slipping back south to Oswego county and weakening/retracting
back toward the lakeshore Tuesday night as the flow across the
eastern half of the lake weakens.

At this point...it appears that snowfall totals may reach 2-3 feet
from the northern Tug Hill region to areas just south of
Watertown...with a larger surrounding envelope of 1-2 foot
accumulations including the Watertown area itself. Meanwhile areas
along the south shore of the lake from Niagara to northern Cayuga
county should see totals of up to 4-8" between late Sunday evening
and Monday...for which Winter Weather Advisories for Lake Effect
Snow have been issued as outlined below. This latter area will need
to be closely monitored in case the snow associated with the lake
aggregate trough/mesolows appears as if it will be a bit heavier
than currently forecast...in which case a shorter-fused upgrades to
a Lake Effect Snow Warning could become necessary.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
A ridge will build into the region for Wednesday and Thursday, which
is expected to cut down on the lake response off of both lakes.
Winds will shift to the south-southwest, resulting in any remaining
lake effect to push north through the day Wednesday and Wednesday
night. 850H temperatures are expected to remain favorable for most
of the period, but drier air moving into the region with the ridge,
will also help cut down on the lake potential. A few weak passing
disturbances for later Wednesday into Thursday will help to keep
lake snow showers to some extent downwind of both lakes, whether
it`s in Canada or the BUF CWA will depend on the day and the winds.

A passing shortwave trough on Friday will help increase the lake
response off of both lakes, while also bringing the lake bands back
south, generally east-northeast of the lakes. A brief increase of
synoptic moisture within the trough is also expected.

As the trough exits to the east and a ridge starts to build into the
region on Friday night, the lake response will once again start to
weaken and shift north. Lake snow will continue to weaken and push
north on Saturday as an area of low pressure tracks just north of
the area and the frontal boundaries come into play. There is still
too much uncertainty among the various guidance packages for the
Saturday setup.

Temperatures for the period will start out well below normal for
Wednesday with highs in the single digits to low teens. Day-to-day
warming will bring temperatures back close to normal by Saturday
with highs in the mid 20s to low 30s. 850H temperatures will remain
around -14C or colder through Friday afternoon, before warm air
advection increases these values to above -10C through the day on
Saturday.

&&

.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
Northerly winds will continue across western and north central NY
this morning. Weak lake effect snow showers will be possible across
western NY through this morning. Ceilings are mostly MVFR with VFR
between the lake clouds, mainly across KROC and KART. Moisture will
approach the region from the south and ceilings will likely move
back into MVFR. Light snow showers will brush up against the region
this afternoon. This will cause a period of light snow showers,
mainly south and east of the TAF sites. Lake effect snow showers
will develop near the Lake Erie shoreline and the southern shoreline
of Lake Ontario tonight. This activity has a greater potential to
bring IFR or below conditions at KJHW, KIAG, and KROC into Monday
morning.

Outlook...

Monday through Wednesday...Local LIFR in lake effect snow east of
the lakes, mainly VFR elsewhere.

Thursday...Mainly VFR.

&&

.MARINE...
Light winds will continue on the Lakes today.

A prolonged period of Small Craft Advisory conditions will occur
tonight and through most if not all of next week as one of the
coldest airmasses of the season, and in a few years for that
matter passes over the eastern Great Lakes. As such the
combination of cold temperatures and breezy winds will bring
freezing spray to at least Lake Erie, and possibly Lake Ontario
as well from time to time through Thursday morning.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory from 10 PM this evening to 4 PM EST
     Monday for NYZ001>003.
     Winter Weather Advisory from 1 AM to 7 PM EST Monday for
     NYZ004-005.
     Lake Effect Snow Warning from 1 PM Monday to 1 PM EST
     Wednesday for NYZ006.
     Lake Effect Snow Warning from 1 PM Monday to 7 AM EST
     Wednesday for NYZ007-008.
     Lake Effect Snow Warning from 10 AM Monday to 4 AM EST
     Wednesday for NYZ010-011.
     Lake Effect Snow Warning from 1 AM Monday to 10 AM EST
     Wednesday for NYZ012-020-085.
     Lake Effect Snow Warning from 7 PM this evening to 10 AM EST
     Wednesday for NYZ019.
MARINE...Heavy Freezing Spray Warning from 1 AM Monday to 1 AM EST
         Wednesday for LEZ040-041.

&&

$$

SYNOPSIS...HSK/Thomas
NEAR TERM...HSK/TMA
SHORT TERM...JJR
LONG TERM...SW
AVIATION...HSK/TMA
MARINE...HSK/Thomas