Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 011420

Area Forecast Discussion
National Weather Service Buffalo NY
920 AM EST Thu Dec 1 2016

In the wake of a cold front, a colder airmass will overspread the
region for the remainder of the week, with lake effect rain showers
east-northeast of the lakes today shifting southward and becoming
mixed with wet snow tonight and Friday, before gradually diminishing
Saturday and Saturday night.


Cold air continues to flow across the Eastern Great Lakes region
today, with temperatures at 850 hPa dropping to around -4 to -6C.
This will be cold enough to generate a lake effect response. A band
of lake effect rain is ongoing off Lake Erie this morning, with a
band in its infant stages off Lake Ontario as low level moisture is
just now beginning to return over the lake. A shortwave on water
vapor imagery is nearing the western end of Lake Erie this mid-
morning. Expect this band of rain off Lake Erie to generally remain
in place until about 18Z or which time the upstream
shortwave should be passing by, and winds begin to veer some.

Off Lake Erie...A band of rain is now oriented across Northern Erie
County and in a weakening state extending northeastward towards
Monroe County. This band will be capable of producing a solid three
quarters of an inch to inch of rainfall where it is most persistent
across the western counties today...followed by another general half
inch of precipitation tonight. Across the higher terrain well south
of Buffalo...some of this will manifest itself in slushy snowfall
accumulations of 1 to 3 inches tonight.

Meanwhile off Lake Ontario...a band of lake effect rain will
continue to form on a general 250-260 degree flow...which would
place the activity between Watertown and northern reaches of the Tug
Hill Plateau...where it will then persist and slowly get better
organized through much of the rest of the day. Like its Lake Erie
counterpart...the Lake Ontario lake effect will then gradually shift
southward to the Tug Hill proper late today and tonight as the low
level flow veers more westerly behind the upper level shortwave.
Expect this activity to produce as much as a half inch of rainfall
today and anywhere from a half to three quarters of an inch of
precipitation tonight...some of which will likely come in the form
of a slushy 1-3 inch snowfall across the higher terrain.

Outside of the main lake effect areas...conditions will simply
be cooler and fairly cloudy...with just a low chance of some much
spottier rain showers today...and mixed rain/wet snow showers
tonight. Expect today`s highs to range from the upper 30s across
the Southern Tier to the lower and mid 40s elsewhere...with lows
tonight then mostly ranging through the 30s. The cooler weather
will also be accompanied by fairly breezy to windy conditions
through at least the first part of tonight...with sustained winds
of 15-25 mph and gusts to 30-40 mph fairly commonplace...and
the windiest overall conditions expected along the lakeshores
and along the fringes of the main lake effect bands.


Despite the presence of some lake effect showers and marginally
colder late Fall will be remarkably uneventful during this
period. While we have now started "meteorological winter" (post Dec
1st)...there are no strong signs that astronomical Fall will end
anytime soon.

That being said...the overlying pattern through the weekend will
feature a split jet over the country that will include a progressive
low amplitude flow along the length of the Canadian border. As if
that were not enough in regards to blocking any true cold air from
making it to the `Lower 48` unusually deep mid level
circulation over the Pole will short circuit Siberian air from
crossing to the Canadian Archipelago. There will be a slug of cold
air that will manage to slip south to the Canadian Rockies...but
that air will greatly modify before it makes the long journey to the
Great Lakes. As for the day to day details...

A broad mid level circulation anchored over far eastern Quebec will
keep a trough extended back across the Lower Great Lakes Friday and
Friday night. The typical lack of strong winds within the trough
will align with a strengthening +130kt H25 jet that will be shifting
northward from the Ohio Valley to produce a swath of channelled
vorticity over the Lower Great Lakes. This will help in the overall
synoptic lift that will be enhanced by the lake driven instability.

While there will be a smattering of nuisance rain and wet snow
showers across the region within the moist cyclonic flow Friday and
Friday night...the lake enhanced activity will be focused east of
both lakes. Initially...a well aligned 270-280 flow will be found
over both Lakes Erie and Ontario...directing the bulk of the rain
and wet snow showers over the Western Southern Tier and Tug Hill
respectively. The activity will be tempered by a relatively low cap
of 7k ft over Lk Erie and 10k ft over Lk Ontario...with a less than
impressive depth to the snow dendritic growth zone. While there will
be the likelihood of a quarter inch of liquid in the focused
areas...temps in the lowest couple thousand feet will be above
freezing. This should limit daytime snow accums to an inch or
less...possible up to two across the Tug Hill.

The low level flow will veer to around 300 deg Friday night...while
the cap will further lower a couple thousand feet. The focused areas
of mixed rain and wet snow will settle south as a result...becoming
more common over southern parts of Chautauqua and Catt Co`s as well
as over Oswego...Nrn Cayuga and eastern Wayne Co`s. The mixed pcpn
will change to snow in these areas with an additional couple inches
of accumulations possible. Mins Friday night will range from the mid
30s near the lake shores to the upper 20s in the coldest Srn Tier
Valleys and across parts of the Eastern Lake Ontario region.

On Saturday...broad ridging over the Upper Great Lakes will
gradually build east while its associated surface high will become
centered over the Ohio Valley. The limiting subsidence inversion
over the Lower Great Lakes will correspondingly lower even more to
the point where any lake induced convection will be around 5k ft
deep. Given the short fetch from the 300-310 flow and confluent flow anticipating that the lake response will noticeably
weaken. While the lowest portion of the boundary layer will be a
couple degrees not expecting more than a half to one
inch of additional snow accums southeast of either lake during the
day Saturday. Outside of these lake snow will be
seasonably chilly with a passing flurry or wet snow shower.

Ridging will build across our forecast area Saturday night and
Sunday. While this will finally bring an end to the prolonged
nuisance lake supported pcpn event...the increased areal coverage of
fair weather will be short lived. A potent shortwave within a
negatively tilted trough will push across the Lower Great Lakes
Sunday night. This will produce a round of scattered rain and wet
snow showers...with the emphasis on the frozen p-type.


The big story during this period will be the phasing and subsequent
amplification of the longwave pattern over the continent. A very
strong shortwave will dive south from British Columbia on Sunday...
and this will eventually lead to a deep closed low over the northern
plains. Meanwhile...a strong downstream ridge will amplify over the
east. This pattern will direct a surge of cold air southward across
the Inter-Mountain west...but the opposite will be true for the
eastern third of the country where temperatures should once again
climb to well above normal levels.

The medium range ensembles are in general agreement with this
scenario...although the ECMWF is more pronounced with the
amplification and thus the anomalous nature of the temperatures
across the `Lower 48`.

Looking further down the road...the cold air over the western half
of the country is forecast to make its way across the Great Lakes
and Ohio Valley during the second half of the week. There is
relatively high confidence of this change to more wintry weather...
as H85 temps are expected to finally drop into the negative teens c.
This cold air will likely be accompanied by plenty of synoptic
moisture by the end of the the stacked storm system from
the northern plains will cross by to our north. If this scenario
would hold true...then the stage would be set for a significant lake
effect snow event. The question would then relate to the low level
flow...which at this time cannot be answered with any degree of
confidence. Stay tuned.


In the wake of a cold front today will be mostly cloudy...with
lake effect rain showers east-northeast of the lakes affecting
areas in the vicinity of the KBUF/KART terminals. Conditions will
generally be a mix of MVFR and VFR...with the MVFR conditions
tending to be across the higher terrain and within the lake
effect rain showers.

Tonight the lake effect rain showers will shift southward as the
low level flow veers more westerly...while also becoming mixed
with snow showers with nocturnal cooling of the boundary layer.
Expect MVFR/IFR conditions to predominate within the lake effect
precipitation...with MVFR/VFR conditions prevailing elsewhere.

Friday through Sunday...Mainly VFR with areas of MVFR/IFR and
rain/snow showers east of the lakes.
Monday...MVFR with a chance of rain and snow showers.


A brisk general westerly flow (with winds to as high as 30 knots)
will be found across the Lower Lakes region right through Friday...
before veering to northwesterly and gradually diminishing Friday
night and Saturday. As such...small craft advisories remain in
effect as outlined below.


MARINE...Small Craft Advisory until 6 AM EST Saturday for LEZ040-041.
         Small Craft Advisory until 4 AM EST Friday for LEZ020.
         Small Craft Advisory until 1 AM EST Friday for LOZ030.
         Small Craft Advisory until 6 AM EST Saturday for
         Small Craft Advisory until 6 PM EST Friday for LOZ042.
         Small Craft Advisory until 1 AM EST Friday for SLZ022-



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