Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 110840
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
340 AM EST Mon Dec 11 2017

.SYNOPSIS...
Remnant weak lake snows southeast of Lakes Erie and Ontario will end
altogether this morning as high pressure briefly builds across the
region...with fair and largely dry weather otherwise prevailing
today. Low pressure will then cross the region tonight through
Tuesday night...bringing periods of widespread accumulating snow
that will last through Wednesday. Several additional weak systems
will then cross the area late in the week along with additional
chances of snow.

&&

.NEAR TERM /THROUGH TONIGHT/...
Regional surface analysis as of 0830Z shows the arctic cold front
draped along a line from a south of Buffalo to south of Watertown.
In response to the continued southward advance of this boundary...
the Lake Ontario lake snows continue to slide southward and have
weakened into a broad area of light snow extending from Northern
Cayuga county eastward to Lewis County. This activity will continue
to weaken and get shunted southward early this morning...with much
weaker multi-banded lake snows then setting up across areas southeast
of Lake Ontario in the rather sheared northwesterly flow regime
following the frontal passage.

Meanwhile off Lake Erie...a much broader and weaker area of lake
enhanced snow continues across the higher terrain of the western
Southern Tier and Southern Erie/Wyoming counties...just out ahead of
the arctic cold front. Like its Lake Ontario counterpart...this too
will continue to weaken and slide southward with the passage of the
arctic front...with only very weak multibanded lake snows setting up
within the sheared north-northwesterly flow in the wake of the
boundary

Given the above expectations of largely weak and disorganized lake
snows to the southeast of the lakes (and only minor additional
accumulations)...all remaining Lake Effect Snow Warnings will be
cancelled with the forthcoming forecast update.

During the course of today...the remnant weak lake snows southeast
of both lakes will quickly fall apart altogether during the course
of this morning as weak high pressure slides eastward across our
region...the low level flow becomes rather light and even more
sheared...and inversion heights fall to between 3-5 kft. Otherwise
we can expect a welcome quiet and largely dry day under the
transient surface ridge...with daytime highs ranging from the lower
to mid 20s across the North Country to the upper 20s/near 30
elsewhere.

Tonight...our brief period of fair and dry weather will quickly come
to an end...as a slowly strengthening surface low pushes eastward
from the Upper Great Lakes. Increasing warm air advection/isentropic
upglide out ahead of this system will result in widespread light
snow spreading across the region from west to east...with the snow
picking up a bit during the overnight hours as the main surface low
pushes to our western doorstep...and available moisture/lift both
ramp up. At this point total nighttime snowfall accumulations appear
as if they will range from 1-2 inches...with a few spots potentially
receiving between 2-3 inches. Low temps will range from around 20
east of Lake Ontario to the mid 20s elsewhere and should occur
during the first half of the night...before giving way to slowly
rising temps overnight in the warm advection regime out ahead of the
approaching surface low.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
There is high confidence for a widespread general snowfall Monday
night into Tuesday as a clipper low tracks across the Eastern Great
Lakes into Northern NY. Plentiful synoptic moisture and lift will be
forced by an anomalous 2-3 SD below normal, near 500dm, mid-level
trough digging south across the Great Lakes. Additional support for
widespread snow will come from warm advection near 850mb. A blend of
12z QPF guidance with SLR between 15:1 and 20:1 in a cooling airmass
will bring a general 2-3 inches Monday night. As the surface low
begins to center to the east of Lake Ontario Tuesday afternoon,
winds will veer to west then northwest while becoming gusty in
steeping low level lapse rates as cold advection sets in. Additional
synoptic snow is expected areawide through Tuesday in wrap around
moisture where another 2-3 inches will be possible. A Winter Weather
Advisory may be needed especially if snow rates/totals come in
higher with later guidance. Temperatures Monday night will dip into
the teens and low 20s with highs into the mid 20s to around 30
Tuesday. Gusty winds in the wake of the systems cold front should
run 20-30 mph especially south of the low center across the western
Southern Tier driving wind chills into the teens.

Later Tuesday into Wednesday we will see a transition into another
potentially significant lake effect snow event with headlines
possible. Lake effect snows are expected to develop south or
southeast of the lakes as 850mb temps cool aloft. BUFKIT cross
sections indicate healthy lake plumes with equilibrium heights
running 10-15kft and sufficient synoptic moisture and lift
intersecting the dendritic snow growth zone. Tuesday night into
Wednesday will perhaps be the most significant time period of
accumulating lake snows with equilibrium level peaking. With current
Lake Effect headlines in effect and the best period for the next
event still 3 days out we will continue with the mention in the
Hazardous Weather Outlook. The core of the anomalously deep 500mb
low will pass over our region Tuesday night and Wednesday which will
bring the coldest air yet this month with lows dipping into the
single digits to teens Tuesday night and only peaking in the teens
to maybe 20 on Wednesday. Lake effect then continues to look like it
will begin to weaken later Wednesday night as high pressure over the
Ohio Valley is forecast to nose north into western NY.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
Medium range guidance continues to indicate two more clipper lows
working across the Great Lakes later this week and next weekend. A
fair amount of uncertainty remains regarding the timing and
tracking of either of these clipper lows as well as any potenial
lake enhancement. Have continued broadbrush chance POPs for snow
showers through Saturday until more certain details arise in newer
guidance. Temperatures will remain below average through the end of
the week, as the region will remain embedded within longwave
troughiness. The eastern trough may break down over the weekend
which would potentially allow warmer air to return to our region.
Blend of model temperature guidance indicates temps may rise back to
normal by Saturday and possibly above normal for Sunday. If this
occurs rain/snow would be possible Sunday. Longer range guidance
suggests that this break from the cold may only be temporary, as a
longwave trough becomes re-established over the East in the week
following.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
Through this morning...remnant weak lake snows and attendant
reductions to IFR/MVFR east and southeast of both Lakes Erie and
Ontario will continue to sink southward and eventually come to an
end...leaving behind largely dry weather and mainly VFR conditions
for the balance of the day.

Conditions will then deteriorate back to IFR from west to east
tonight as low pressure advances eastward across the Great Lakes and
spreads widespread light snow across the region.

Outlook...
Tuesday through Wednesday...Widespread IFR in periods of snow.
Thursday and Friday...Areas of MVFR/IFR with snow showers likely.

&&

.MARINE...
An arctic cold front will finish crossing the Lower Great Lakes
early this morning. In its wake...weak high pressure will build
across the region today...with moderate northwesterlies tending
light and variable by midday/early afternoon. As a result...winds
and waves will fall below advisory levels during this morning...with
fairly quiet conditions then following for this afternoon.

Low pressure tracking eastward from the Upper Great Lakes will then
pass directly overhead late tonight and Tuesday morning. Winds will
increase in the wake of this system Tuesday through Wednesday...with
another period of solid Small Craft Advisory conditions expected
areawide. On Lake Erie...it is not out of the question that conditions
could approach or even reach marginal gale force levels from Tuesday
into early Tuesday evening...however at this point confidence in this
remains too low for a Gale Watch.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Storm Watch from this evening through Wednesday
     afternoon for NYZ001>008-010>012-019-020-085.
MARINE...Small Craft Advisory until 7 AM EST this morning for LEZ040-
         041.
         Small Craft Advisory until 10 AM EST this morning for
         LOZ043-044.
         Small Craft Advisory until 7 AM EST this morning for
         LOZ042-045.

&&

$$

SYNOPSIS...JJR
NEAR TERM...JJR
SHORT TERM...SMITH
LONG TERM...SMITH
AVIATION...JJR
MARINE...JJR



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