Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 061943

Area Forecast Discussion
National Weather Service Buffalo NY
243 PM EST Wed Dec 6 2017

A persistent flow of cold air across the wide open waters of the
Lower Great Lakes will produce accumulating lake snows in the snow
belts east of both lakes during the next couple of days. The most
significant accumulations are expected tonight into early Friday. It
will then remain cold through the weekend with all areas forecast to
pick up a little snow late Saturday into Sunday.


Cold air continues to deepen this afternoon which is contributing to
the better organization of Lake Effect snows mixed with graupel off
Lakes Erie and Ontario. Lake Effect snow Warnings and Advisories are
in place but we have shifted the start time for the Advisory for
Northern Erie and Genesee counties forward to 140pm as radar shows
the Lake Erie band extending right down the axis of the lake
extending over Metro Buffalo and out to Rochester on the eastern
end. The Lake Ontario band remains extended down the Saint Lawrence
River Valley south the Watertown. The colder air has helped lake
induced equilibrium levels to rise to around 7kft per earlier
aircraft soundings. We expect the cap to continue to rise to around
10k feet over both lakes by this evening. Expecting moderate
snowfall rates within the bands averaging a half to one inch per
hour by tonight tonight.

As far as placement of the lake snow tonight...the band off Lake
Erie is forecast to gradually push south across central Erie County
and Wyoming County to the Southern Tier by daybreak Thursday as the
steering flow will veer to about 260 degrees. This is what the Lake
Effect Snow Warning east of Lake Erie covers for lasting into
Thursday night. Expect snow accumulations across the southern half
of Erie county and Wyoming county overnight up to 6 inches.

Meanwhile off Lake Ontario...winds below 700 mb will remain fairly
consistent...ranging from 240-250 degrees. While this will allow the
lake snows to push south across Watertown...the bulk of the snow
will stay north of the Tug Hill. This will result in the highest
overnight accumulations being found over central Jefferson county
and across the northern tip of Lewis county...with overnight
snowfall amounts forecast to be as high as 6 inches.

Elsewhere across the region...this afternoon and tonight will
continue brisk winds and temperatures to will average close to
seasonal values. Max temps today will generally be in the mid to
upper 30s while mins tonight will be in the mid to upper 20s.

Thursday, significant lake effect snow will continue east of both
lakes as a deep longwave trough remains centered over Quebec. This
will maintain cold westerly flow across the eastern Great Lakes.
Outside of lake effect areas, it will remain dry with even some
sunshine outside of the lake effect clouds.

Lake effect parameters remain favorable with lake induced
equilibrium levels around 10K feet off both lakes. Flow will be well
aligned most of the time. A favorably deep layer of dendritic
crystal growth will be found in the cloud bearing layer beneath the
equilibrium levels.

Off Lake Erie...

Thursday morning the band should be focused along the Lake Erie
shore of Chautauqua County, and extending into the Boston Hills of
southern Erie County and the higher terrain of western Wyoming
County. Boundary layer flow may back ever so slightly Thursday
morning and early afternoon, centering the band across southern Erie
and western Wyoming counties. The band may briefly reach as far
north as some of the more distant southern suburbs of Buffalo from
Hamburg to East Aurora. Later Thursday afternoon boundary layer flow
will veer more westerly, carrying the band back into central
Chautauqua and central/northern Cattaraugus counties.

The eastern end of the Lake Erie band will occasionally extend into
portions of Livingston and Ontario counties, and also the western
and northern portions of Allegany County. Spotty minor accumulations
are likely in these counties, but not enough for any advisories.

The Lake Erie band will likely reach its best organization on
Thursday, with snowfall rates of 1-2 inches possible at times in the
heaviest portion of this band. Storm totals through Thursday night
are still expected to reach 1.5 feet. The highest amounts are
expected across the Boston Hills in southern Erie County, the higher
terrain in southwest Wyoming County, and portions of the Chautauqua
Ridge in northern Chautauqua and northwest Cattaraugus counties.

Off Lake Ontario...

Thursday the band is expected to remain fairly stationary with just
a few minor north/south wiggles. The band should be focused on
central Jefferson and far northern Lewis counties during this time,
including the Watertown area. Snowfall rates may briefly reach
around 1 inch per hour at times Thursday within this band.

Storm total snowfall into Friday morning is still expected to reach
about 1.5 feet in the most persistent bands. This is most likely
across central Jefferson County (likely just inland from Watertown
and away from the influence of warmer Lake Ontario water). Totals
may also approach 1.5 feet across the northern Tug Hill.


Lake effect snow will continue Thursday night and then taper
off during the day Friday. A subtle shortwave will slide into
New England Thursday evening. This will cause winds to briefly
shift to the west, but most 12Z guidance suggests winds will
quickly shift back to the southwest Thursday night. As a
result, the lake effect band off Lake Erie should lift northward
and intensify. The WSW flow late Thursday night will be well
aligned while taking advantage of the long fetch down the length
of Lake Erie. This is supported by high resolution QPF guidance
with the RGEM favored due to its placement of the lake effect
band. This band will continue to lift northward across the
Buffalo metro area and drop a quick few inches Friday morning
before weakening later Friday.

A similar trend will play out east of Lake Ontario, but about 6
hours later. It is possible the band will meander into Oswego
county Thursday night. It is uncertain how long the band will
remain there, with a chance that advisory criteria will be
reached. Outside of lake effect bands, expect mainly dry weather
with partly cloudy skies.

Increasing directional shear and a wind shift to the SSW direction
will cause lake effect snows to taper off and mainly lift out of the
area on Friday. Some light additional accumulations are possible
near the Saint Lawrence River Friday afternoon. The southerly flow
will promote clearing skies south of Interstate 90. Temperatures
will continue to be cold with highs in the upper 20s to lower 30s.

Winds will shift back to the southwest Friday night, but there will
continue to be some directional shear which will inhibit lake
effect snow development. There may be some light snow showers
northeast of Lake Erie and Ontario but no significant
accumulations are expected. Otherwise it will be dry with chilly
overnight lows ranging from the upper teens to upper 20s.

On Saturday a weak surface low across Michigan will gradually
approach the region as it moves with the upper level trough axis.
There will be increasing chances of some light and generally
synoptically driven snow Saturday afternoon. Any accumulations
should be minor and generally confined to far Western New York.


Friday night through Saturday morning will be relatively quiet, with
just a few light snow showers possible northeast of Lakes Erie and
Ontario. Later Saturday afternoon and Saturday night, both the GFS
and ECMWF have trended a little stronger with a clipper moving
across the area. This will bring some general light snowfall to much
of the region, with some lake enhancement likely. The lake
enhancement would initially be east and northeast of the lakes on
west to southwest flow, then move southeast of the lakes by Sunday
morning as boundary layer flow becomes northwest behind the clipper.
Some lake effect snow will continue Sunday southeast of the lakes,
but this appears to be relatively minor at this point. Another
clipper will cross the area Monday and Monday night with some
additional light snow, with another round of northwest flow lake
effect behind it. Significant lake effect snow does not appear
likely Saturday through Tuesday given the frequent changes in wind
direction and disruption from clippers, but a number of minor
snowfalls will produce slick travel at times.

Temperatures will run below normal, with the coldest days likely to
be Sunday and again Tuesday behind each clipper as a fresh batches
of cold air arrive. This cold and active pattern will likely
continue through the 2nd and 3rd weeks of December. The position of
the longwave trough suggests a parade of clippers will cross the
area with frequent light snow and opportunities for lake effect snow
as each fresh batch of cold air moves into the area.


Lake Effect snow has become more organized this afternoon and will
continue to ramp up into this evening as cold air deepens and
moisture increases. KBUF has lowered to IFR VSBY at 18z with KJHW
CIGS running at MVFR. KART is expected to lower to IFR by 21z as
Lake effect snow pushes south over the terminal.

Tonight, lake snows will persist east and northeast of both lakes.
Lake snows are expected to keep MVFR to IFR VSBYS in the vcnty of
KBUF/KART/KGTB but the snows off Lake Erie should push far enough
south to allow KBUF to improve to VFR by 04z but should also remain
mainly north of KJHW. The remainder of the region will keep their
VFR conditions.

Thursday, Lake Effect Snow will remain well organized east of the
Lakes. KART will see the worst conditions remaining in IFR or lower
under the snow band through much of the day. Off Erie, the band is
forecast to generally remain between KBUF and KJHW.

Thursday night...Areas of IFR in heavy lake effect snow
east and northeast of the lakes...with mainly VFR conditions
Friday through Saturday...VFR/MVFR with scattered to occasionally
more numerous snow showers.
Sunday and Monday...IFR in Lake Effect Snows but VFR elsewhere.


Winds have lowered below Gale Force this afternoon. Have dropped the
Warnings and raised Small Craft Advisories which extend into the
weekend due to a fairly tight surface pressure gradient remaining
over the Lower Great Lakes.


NY...Lake Effect Snow Warning from 7 PM this evening to 10 AM EST
     Friday for NYZ007-008.
     Winter Weather Advisory until 1 AM EST Thursday for NYZ010-011.
     Lake Effect Snow Warning from 7 PM this evening to 7 AM EST
     Friday for NYZ012-019-020-085.
MARINE...Small Craft Advisory until 7 PM EST Saturday for LEZ040-041.
         Small Craft Advisory until 7 PM EST this evening for
         Small Craft Advisory until 7 PM EST Saturday for
         Small Craft Advisory until 7 AM EST Saturday for LOZ042.
         Small Craft Advisory until 5 PM EST this afternoon
         for SLZ022-024.



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