Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 042159
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
459 PM EST Sun Dec 4 2016

.SYNOPSIS...
A weak disturbance will pass over the area tonight, producing a
several hour period of widespread light snow. Minor accumulations
are likely over the higher elevations. Another surface high will
bring a short break from the unsettled conditions Monday afternoon
and night before our weather will become quite active for the
remainder of the week. This will include a trend towards wintry
weather after Wednesday when significant lake snows will impact
areas east of both lakes.

&&

.NEAR TERM /THROUGH MONDAY/...
...Light snow accumulation to bring periods of slick travel starting
this evening into Monday morning...

Uneventful into early this evening as clouds will be on the
increase from the west as surface high pressure and upper level
ridging slowly depart.

The weather certainly looks to turn more active this evening and
tonight as an upstream shortwave trough races northeast, becoming
negative tilted in the process. Attendant strong surge of
isentropic lift collocated nicely with plume of deeper moisture,
both of which are set to slide through our area tonight. Thermal
profiles are marginal to start the event, so initially expecting a
rain/snow mix as precipitation arrives into the west this evening.
Magnitude of lift and cooling through the melting process should
transition all areas over to snow rather quickly although lake
modification may keep areas right along the Lake Erie and Lake
Ontario shorelines in a mixed precipitation regime a but longer.

Latest mesoscale models similar in showing a rather quick moving
system, but given forcing and available moisture, hard to argue
with guidance blend QPF totals of around a quarter or so. To
complicate matters, low level thermal environment remains cold
enough for some potential lake enhancement off both Lake Erie, as
well as Lake Ontario on a general westerly flow regime. Cooling
thermal profiles and strong support for periods of enhanced lift
in the dendritic growth layer suggests snow-to-liquid ratios
pushing 12:1 values, especially for interior section. All in
all, continuity amounts of 1-3"/2-4" snow totals still look
reasonable, with the highest amounts centered across interior
higher elevations of the western Southern Tier and Tug
Hill/Western Adirondacks, where localized amounts could push
toward 5" if there is a better contribution from lake
enhancement. Probably no more than a coating to an inch for the
lower elevations along the lakeshore.

As we get in to Monday morning, the snow winds down from west to
east as forcing races off to the northeast. We may even see a brief
period of drizzle/freezing drizzle as mid level moisture departs.
Post-system airmass remains cold enough for some continued lake
contribution as winds turn northwest. Lake equilibrium levels
remain awfully shallow, suggesting any lingering lake effect snow
showers will remain light at best.

Headline considerations, at this point, we are expecting a
widespread snowfall event with accumulations remaining just advisory
levels, with some travel impacts, especially overnight and early
Monday morning when snowfall rates overcome initial warm road
conditions. Since specific criteria is not expected to be met,
have decided to forgo specific headlines and will use the HWO and
SPS products accordingly and as needed to handle any specific
impacts.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
Any lingering light snow/drizzle east of Lake Ontario Monday night
will end through the evening hours as lake inversion heights fall,
and moisture falls beneath the good snow dentritic growth zones.
Otherwise the night will be dry with some breaks in the clouds.

Tuesday will begin dry as a ridge of high pressure crosses the
region. A closed low seen over western Mexico Sunday afternoon will
open up as it races northeastward across the United States Monday
and Monday night. This feature will bring the next period of
unsettled weather through the midday hours Tuesday, and then into
Tuesday night. Given the source region of this shortwave within the
Southern Branch of the jet stream there will be more rain than snow
falling Tuesday, though through the night a few lower elevations
could see a mix of wet snow/rain in addition to the snow falling
over the higher terrain. Snow accumulations will be minor, with
again a general inch or two across higher terrain.

There may be lingering precipitation early Wednesday across the
region, and likely east of Lake Ontario where a moist, upslope flow
will maintain precipitation through the morning hours. A ridge of
high pressure extending across the Plains, will briefly extend
eastward towards the Eastern Great Lakes region, a spell a brief
period of dry weather before cold air advection under cyclonic flow
aloft, and moist westerly flow increases chances for light snow east
of the lakes later Wednesday night.

High temperatures will run a few degrees above normal, with
afternoon temperatures reaching the upper 30s to lower 40s Monday
and Tuesday. There will be no bitter cold this period with
overnight lows in the mid 20s to mid 30s.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
The period will feature cold temperatures with frequent opportunities
for snow. 12Z model guidance has trended away a potential
synoptic system, with a consensus now suggesting most of the snow
will be lake effect or at least lake enhanced. There is still
uncertainty in the wind direction and thus the location of lake
effect snow. There is the potential for significant snowfall,
especially considering the prolonged nature of the event which
runs Thursday through Saturday. Now for the details...

On Thursday a trough will dig across the Great Lakes region,
which will advect much colder air into Western New York. 850mb
temperatures will plummet and will average -12C to -14C across
the region Thursday night through Saturday. This will be cold
enough to support lake effect snow, with precipitation changing to
all snow by Thursday afternoon. The cyclonic flow aloft will
provide ample moisture, with embedded shortwaves likely to provide
periodic enhancement. For Thursday and Thursday night, it appears
that a WNW flow will be predominant. This may support banding east
or southeast of Lake Ontario, with less organized but persistent
bands off Lake Erie due to upsloping and moisture from Lake Huron.

On Friday and Friday night, predominantly a NW flow is expected,
which would continue lake effect snows but push the steadiest
snows a bit southward. By Saturday the upper trough axis will
shift east of the New England coast, with a weak surface high
building behind it across the Great Lakes region. This should
bring in slightly drier air and lower equilibrium levels, but
conditions still support localized lake effect snows to continue.
Winds are forecast to veer to the southwest and eventually the
south by Sunday. This would lift what is left of lake effect snow
bands northeast of the lakes.

Although consensus agrees on the cold pattern, there is still a
considerable spread among model guidance in terms of specifics.
Even a subtle shift in winds would significantly impact the
location of the heaviest snows. This said, the pattern generally
favors the greatest amounts southeast of Lake Ontario (probably focused
near Oswego county) and the Western Southern Tier. It is still too
early for specific snowfall amounts and even these areas of focus
may change as new model guidance becomes available.

Otherwise, temperatures will be considerably colder than they have
been with highs on Friday and Saturday ranging from the mid 20s to
around freezing. The forecast favors a blend of raw model
guidance due to the wind and cloud cover which will limit daytime
heating and radiational cooling.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
Ceilings have improved to VFR at many locations this afternoon.
The exception is at KJHW where ceilings will likely hover near 3k
or just below through the afternoon.

Tonight...a disturbance over the Ohio valley will push northeast
across the Lower Great Lakes. This feature will produce widespread
light snow with high confidence that conditions will deteriorate to
at least MVFR levels. The snow will likely reduce vsbys to IFR
levels for a period of several hours after 03z.

Outlook...
Monday...MVFR with a chance of rain and snow showers.
Tuesday...Mainly VFR.
Tuesday night and Wednesday...VFR deteriorating to MVFR with some
rain becoming likely.
Thursday and Friday...MVFR/IFR with snow likely.

&&

.MARINE...
Weak high pressure will slide east this evening. A disturbance with
widespread light snow will push across the region tonight, winds are
not expected to notably freshen until Monday when the gradient will
temporarily tighten between the exiting system and the next surface
high. A period of small craft advisories will likely be needed.

Winds and waves will subside with the arrival of another surface
high overnight Monday night.

While winds will freshen from the east on Tuesday, but they will
remain below small craft advisory levels as the higher waves will be
confined to Canadian waters.

Looking further ahead, a deep storm forecast to track across
James Bay late in the week may generate gale force winds over the
Lower Great Lakes Thursday night and Friday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 4 AM to 7 PM EST Monday for LEZ040-
         041.
         Small Craft Advisory from 10 AM to 10 PM EST Monday
         for LOZ043-044.
         Small Craft Advisory from 7 AM to 7 PM EST Monday for
         LOZ042.
         Small Craft Advisory from 1 PM to 10 PM EST Monday for
         LOZ045.

&&

$$

SYNOPSIS...TMA
NEAR TERM...TMA
SHORT TERM...THOMAS
LONG TERM...APFFEL
AVIATION...TMA
MARINE...TMA



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