Area Forecast Discussion
Issued by NWS Buffalo, NY

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503
FXUS61 KBUF 041953
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
253 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 SATURDAY/...
This period will feature a major pattern change across our region...
as deep upper level troughing develops across eastern North America
and drags much colder Canadian air into our region...with 850 mb
temperatures consequently dropping off into the negative mid teens
by the end of the week. For our area...this will translate into
the arrival of considerably more wintry temperatures later on in
the week...as well as the development of potentially significant
lake effect snows downwind of the Great Lakes.

As the trough digs toward our region early on in the period...it
should spur the development of yet another wave of low pressure on
its eastern flank during the Wednesday night-Thursday time frame...
though the medium range guidance continues to exhibit considerable
differences with the timing and strength of this wave...with the
00Z/04 ECMWF remaining consistently deeper and slower with this
feature than the much weaker and faster GFS.

For our region...this wave will likely bring another round of
fairly widespread snow and rain showers as it passes through our
region later on in the week...with these remaining centered on
Thursday at this time following both a model consensus approach
and our existing continuity.

Following the passage of this wave...much colder Canadian air will
then flood across our region through the remainder of the week as
highlighted above. Coupled with what should be plentiful moisture...
this will set the stage for a round of potentially significant lake
snows Thursday night through Friday night...with these then likely
weakening at least some and shrinking up in coverage on Saturday as
high pressure and drier air ridge into our area from the Central
Great Lakes and Ohio Valley.

With respect to the location of the lake snows...current guidance
continues to suggest that the large-scale flow across our region
will generally be westerly to west-northwesterly once the colder
air arrives later on in the week...which would tend to direct the
most significant lake snows across the traditional snow belts east
and east-southeast of the lakes. The above stated...attempting to
pin down exact band locations this far in advance is generally a
fruitless enterprise as much can still change...with even small
variations in the low level wind field having a large influence
on lake band positions and consequently the areas of greatest
overall forecast concern. With this in mind...it will likely be
at least a few more days before the exact details of this next
event begin to become more clear.

As for temperatures...these will progressively lower through the
period...with daytime highs in the mid to upper 30s Thursday
dropping off to typical midwinter levels in the mid 20s to lower
30s in time for both Friday and Saturday.

&&

.AVIATION /20Z 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 will likely generate gale force winds
over the Lower Great Lakes Thursday night and Friday.

&&

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

&&

$$

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



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