Winter Storm Watch 10, NWS Buffalo, NY

Area Forecast Discussion
National Weather Service Buffalo NY
148 PM EST Sun Dec 17 2023

.SYNOPSIS...
Low pressure tracking along the Atlantic coast will bring
moderate to heavy rainfall tonight into Monday for areas east
of the Genesee Valley, and especially toward Central NY. Rain
will change to snow late Monday, with accumulating snows east of
Lake Erie through Tuesday morning. A drier stretch of weather
returns late Tuesday through the rest of the week.

&&

.NEAR TERM /THROUGH MONDAY/...
Early this afternoon radar shows rain across Chautauqua County
and areas north and west of Buffalo. Steadier rain will spread
across the rest of the forecast area through early evening. Although
this will be a very dynamic system, the deeper maritime moisture
is well to the south now, so rainfall through this evening will
not be terribly heavy since it's mainly being driven by the
trough and not the coastal low. Gusty southerly downslope winds
will diminish with the start of the rain, but still could see
some gusts of 30 to 40 mph this afternoon.

Tonight, low pressure tracking along the Atlantic coast will
merge with the northern branch shortwave, intensifying into a
major storm as it tracks across New England on Monday. This will
set up a strong southerly flow across southern New England (90+
kts at 850mb) which will tap into Atlantic/GOMEX moisture.
Models have trended east and are now in agreement that our area
will be on the western fringe of this system, with the deepest
moisture and strongest LLJ staying to our east. There will be a
sharp cut- off in the heavy rainfall amounts, with a westerly
flow keeping the moisture away from the Genesee Valley westward.
Heavy rain will clip the eastern Lake Ontario region, late
tonight into Monday morning, with around 2 inches of rain
expected here. Have trended down rainfall amounts across the
rest of Western NY with only a quarter to half inch expected
from Rochester westward. In fact, the rain may even taper off
across far Western NY late this evening as the LLJ weakens
there.

Based on these trends and the lack of snow pack, the flood risk
is relatively low. The Black River and its tributaries are
likely to reach action stage, but MMEFS ensembles show low
chances for these to flood.

On Monday, steady rain from Rochester east will end from west to
east as the storm system moves north and mid-level winds shift
to the northwest. This will usher in cooler air aloft, which
will eventually change rain over to snow across higher terrain
late Monday afternoon. 850mb temperatures will only drop to
around -5C across Lake Erie by sunset Monday which is not cold
enough to support lake effect yet. There will be upslope
enhancement across higher terrain, with maybe a slushy inch of
accumulation across higher terrain in the Southern Tier. Lower
elevations should remain all rain during the daylight hours.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
Monday night through Tuesday morning the sharp mid level trough
and deep wrap around moisture will cross the eastern Great
Lakes. Rain will continue to change to snow from west to east.
Snow will become widespread across the entire region later
Monday night through early Tuesday morning as forcing and
moisture maximize. Lake enhancement and northwest upslope flow
will be superimposed on the general area of synoptic snow,
enhancing snowfall rates and amounts southeast of Lake Erie and
Lake Ontario and across higher terrain. The dendritic growth
zone becomes quite deep and nearly saturated later Monday night
through early Tuesday, supporting increasing snow:water ratios
after an initially slushy start to the event.

Model guidance continues to suggest the best and longest lasting
juxtaposition of large scale forcing, lake enhancement, and upslope
flow will focus along the Chautauqua Ridge. Early estimates suggest
a narrow zone of 5-8" along the Chautauqua Ridge, with a broader
area of 3-5" across the higher terrain east of Lake Erie including
the Boston Hills, ridges of western and central Wyoming County, and
western/northern Cattaraugus County. There is at least some
potential for low end warning amounts along the Chautauqua Ridge,
but the areal footprint of this potential is very limited so we will
hold off on a Watch for now.

Elsewhere across the rest of the area, expect snow amounts Monday
night through Tuesday to be in the 1-3" (spotty 4") range, with the
higher end of that range most likely for higher terrain and along
the south shore of Lake Ontario with lake and upslope enhancement.
Snow amounts will be limited, but the combination of snow and
falling temperatures will impact travel, including the Tuesday
morning commute.

The widespread snow of Tuesday morning will quickly taper off from
west to east from late morning through the afternoon as the mid
level trough moves east to New England and is rapidly replaced by a
building surface ridge and dry air. Snow will be mostly over by
midday across Western NY, with the last of the lake effect snow
showers ending southeast of Lake Ontario by Tuesday evening.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Another extended period of mainly dry weather will start Wednesday
and last through the end of the week as a broad upper level ridge
dominates the central and eastern US. Surface high pressure will
remain in place over the eastern US Wednesday through Friday with
dry weather and temperatures running a few degrees above average.

Friday night and Saturday a weak system meandering through the mean
upper level ridge will drift into the Ohio Valley. Most operational
and ensemble model runs have kept this weak system west of our area,
although the 00Z ECMWF brings some light precip into Western NY by
late Friday night and Saturday with rain or rain/wet snow mix. Even
if this materializes, the weak nature of the system will keep
amounts very light with minimal impact.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Mainly VFR flight conditions at the start of the 18Z TAF cycle
will deteriorate this afternoon and evening. It will start with
mainly MVFR cigs developing following the start of rainfall
which will move from west to east across the area. Then lower
cigs and some fog are expected tonight as a surface trough moves
through and winds shift from the south to the southwest and
eventually northwest. Heavier rain is possible late tonight into
Monday at KART with vsby restrictions. Otherwise, LLWS at KJHW
and KART will diminish later this afternoon when the LLJ
weakens.

Steady rain will end from west to east late tonight through
mid-day Monday. There will be lingering showers along with
IFR/MVFR cigs for much of the day. Cooler air will build in,
changing rain to snow across higher terrain Monday afternoon.

Outlook...

Monday night...MVFR/IFR with rain and snow showers changing to
all snow and generally decreasing in coverage.

Tuesday...MVFR improving to VFR. Leftover snow showers east of
the lakes ending.

Wednesday through Friday...VFR.

&&

.MARINE...
This afternoon and tonight winds will temporarily weaken as a
relative lull develops across the Lower Great Lakes
Region, before picking up markedly out of the northwest Monday
and Monday night as a coastal low tracks northeastward across
New England and intensifies. This will likely necessitate
another round of high-end Small Craft Advisories...with
northwesterlies to 30 knots expected at times Monday and Monday
night.

&&

.CLIMATE...
...RECORD WARM LOW TEMPERATURES LIKELY TO BE BROKEN TODAY...

While record highs are fairly safe today, the record warm low
temperatures are in jeopardy for all 3 of our climate sites.
Last night, since midnight Buffalo has not dropped below 48F,
Rochester 47F, and Watertown 45F. Based on the current
forecast, temperatures are not expected to drop below the
records for December 17th before midnight tonight.

Record warm minimum temperatures for December 17th...

City 		Temp (Year)

Buffalo 	43 (1921)
Rochester 	44 (2012)
Watertown 	42 (2012)

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

SYNOPSIS...Apffel/SW
NEAR TERM...Apffel
SHORT TERM...Hitchcock
LONG TERM...EAJ
AVIATION...Apffel
MARINE...Apffel
CLIMATE...Apffel

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