Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 050022
AFDBUF

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

.SYNOPSIS...
A weak disturbance will pass over the area tonight, producing a
several hour period of widespread light to moderate snow. Minor
accumulations are most 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 to moderate snow accumulation to bring periods of slick
travel starting this evening into Monday morning...

An upstream trough is becoming negatively tilted while racing across
the Central Great Lakes this evening. Attendant strong surge of
isentropic lift collocated nicely with plume of deeper moisture,
both of which are set to slide through our area overnight. Thermal
profiles are marginal to start with the 00z KBUF RAOB showing dry
and unstable environment through 850mb with a warm advection
associated inversion above 850mb. Surface temperatures across
western NY are still above freezing but readings are in the 20s east
of Lake Ontario. First radar returns over western NY should be just
virga with dry low levels but expect onset of precip to occur near 9-
10pm in the western counties. 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.

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 weak 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 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.

The worst conditons should be waning across western NY by the time
the morning commute is in full swing while the eastern Lake
Ontario region will likely see the height of the event centered on
the morning commute.

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 under
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 /01Z MONDAY THROUGH FRIDAY/...
VFR cigs at 00z will deteriorate to MVFR with isolated IFR later
this evening with the arrival of a rain/snow mix changing over to
all light to moderate snow. This is associated with a disturbance
that will push northeast across the Lower Great Lakes. The snow will
likely reduce vsbys to IFR levels at all sites for a period of
several hours after 02-03z in western NY and 06-07z for Central NY.

The disturbance will shift east of the area on Monday with snow and
associated worst conditons ending by 12z for western NY but holding
through the morning for central NY. MVFR level cigs will the linger
through the rest of Monday in the wake of the disturbance.

Outlook...

Monday night...MVFR cigs improving to VFR. 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...
A disturbance with widespread light to moderate snow will push
across the region overnight, 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 has been issued for the nearshore waters on
Lakes Erie and Ontario.

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...SMITH/TMA
NEAR TERM...SMITH/TMA
SHORT TERM...THOMAS
LONG TERM...APFFEL
AVIATION...SMITH/TMA
MARINE...SMITH/TMA



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