Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 130647
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
147 AM EST Wed Dec 13 2017

.SYNOPSIS...
A cold northwesterly flow will result in continued lake effect snow
and blowing snow across the region today. A short break is possible
this coming evening before another weak system moves into the region
tonight. Yet another system with both some lake effect and
widespread snow will move in by Friday and last through least part
of the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
A deepening surface low continues to move northeast across the Gulf
of Maine early this morning as an anomalously deep upper level
trough plows into the Lower Great Lakes region. Behind the low,
northwest flow continues to drive lake effect snow over the southern
lakeshores. A southward pushing surface trough/arctic boundary will
back steering flow pressing lake bands south and west this morning.

Off Lake Erie, a single stronger bands remains embedded within
weaker multibands. The strongest band which is sliding to the
south across Chautauqua county as the surface trough presses
south across Lake Ontario has a Lake Huron connection supporting
the better organized lake band. The bands should begin to
migrate slowly back north in a weakening state after daybreak as
the next system approaches. Lake Effect Warnings will remain in
place.

The Niagara Frontier has recently come under increasing snow
intensity as some of the Lake Ontario multibands press southwest on
the nose of the surface trough/arctic boundary. In addition, there
will be plenty of blowing snow to warrant the continuation of a
winter advisory into this morning.

Resulting (additional) snow accumulations through today will vary
substantially from location to location due to transitory banding,
but here are a few areas of interest:
* Inland Chautauqua County:  6-10 inches.
* Buffalo area Southtowns:  4-7 inches
* Other higher terrain...:  4-8 inches.
* Niagara Frontier.......:  1-2 inches.
* Allegany...............:  T-4 inches.

Off Lake Ontario, the surface trough/arctic boundary is also
pushing multibanded snow to the south and west. These will
primarily affect Wayne county east through western Oswego
County. A connection to Georgian Bay continues to provide
additional support for an embedded stronger band shifting across
Northern Cayuga near 1am. Resulting (additional) snow
accumulations through today will vary substantially from
location to location due to transitory banding, but here are a
few areas of interest:

* Shorelines west of Rochester: 1-2 inches
* Rochester Area..............: 3-6 inches
* Wayne to Oswego.............: 6-10 inches
* Tug Hill Plateau............: 5-9 highest south
* Watertown...................: 2-4 inches

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
Some lake effect snow may linger Wednesday evening southeast of Lake
Ontario, mainly across northeast Wayne, northern Cayuga, and
southern Oswego counties. This may produce another 1-3 inches before
breaking up overnight.

The 06Z and now the 12Z model guidance has trended a little farther
north and a little stronger with the next clipper, set to move
through PA Wednesday night. A period of DPVA ahead of the associated
mid level shortwave will combine with a broad area of warm advection
and isentropic ascent to the north of the low track to produce a
period of weak lift across the region. This will bring an area of
light, accumulating snow to at least the Southern Tier, possibly
spreading up into the Thruway corridor as well. Expect the snow to
enter Chautauqua County by late afternoon Wednesday, then spread
into the rest of Western NY during the early evening, reaching
central NY by late evening. What remains of the lake effect snow
over Lake Ontario may help to moisten the low levels enough to bring
some light synoptic snow all the way to the south shore of Lake
Ontario. Amounts will be light with this system, with around 2
inches across the western Southern Tier, and an inch or less from
the Thruway northward. The North Country should remain dry.

Any remaining synoptic snow will quickly end early Thursday morning.
A cold northwest flow in the wake of this system will allow some
limited lake effect snow to develop southeast of Lakes Erie and
Ontario Thursday and Thursday night, but a fairly dry background
synoptic scale airmass should keep accumulations somewhat limited.
This may produce 1-2 inches Thursday, and another 2-3 inches
Thursday night in persistent bands. Off Lake Erie, this would
primarily focus on the Chautauqua Ridge, and off Lake Ontario mainly
across Oswego County, and far northern Cayuga County. Outside of
lake effect areas, expect mainly dry conditions with just a few
flurries or light snow showers Thursday. Temperatures will remain
cold, with highs in the upper teens to lower 20s in most locations.
The higher terrain east of Lake Ontario may struggle to reach 10.

Late Thursday night and Friday morning boundary layer flow will back
to the west and southwest ahead of the next system. This will carry
the Lake Erie lake effect northward across Buffalo, and the Lake
Ontario band northward across Watertown Friday morning. The bands
should not be particularly strong at that point given the lowering
inversion heights and quickly backing winds, but could drop some
minor accumulations.

Later Friday afternoon and Friday night yet another clipper will
cross the region. This time, the surface low will pass to the north
of the area across Southern Ontario. This will produce another round
of light snow across the region, with lake enhancement developing
east and northeast of the lakes which may add an extra few inches to
what is otherwise a minor snow event.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
A ridge builds in Saturday in the wake of a trough passage Friday
night. With cold air and moisture in place Saturday morning behind
the trough, lake effect snows would be ongoing downwind of the
eastern Great Lakes. However, the ridge and warm advection quickly
move in during the day Saturday, which will shut down any lingering
lake snows.

The pattern deamplifies briefly for Sunday into Monday, with a
slightly more zonal, Pacific influenced flow across the Great Lakes.
Temperatures will be more mild, with daytime highs in the 30s both
day. Transient shortwaves will provide a few chances for snow
showers, and possibly some mixed precipitation. Beyond that, the
next cold push of air comes late Tuesday into Wednesday.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
Lake snows south of both lakes will continue to result in IFR vsbys
...otherwise scattered snow showers will accompany VFR to
occasionally MVFR conditions elsewhere. A frontal boundary sagging
south across the region has returned KBUF/KIAG to IFR levels early
this morning.

IFR to MVFR conditions will continue for most locations to about 18z
with KART likely seeing the most improved conditons of all TAF sites
under northwest flow. The lowest vsbys for the lake snows will be
found at KJHW where LIFR conditions should persist.

Lake snows east of both lakes will gradually diminish this afternoon
with IFR to MVFR conditons briefly improving to VFR by the end of
the day. Tonight, another clipper will shift south of NY but will
bring back additional widespread light snow and IFR especially toward
the southern half of western NY after 00z Thursday.

Outlook...

Thursday through Sunday...Several systems will move across the
region over the course the the week and weekend with both widespread
snow and localized lake effect with resulting IFR conditions.
There will be several periods of VFR between systems.

&&

.MARINE...
A deepening surface low continues to move northeast across the Gulf
of Maine this morning as an anomalously deep upper level trough
plows into the lower Great Lakes region. Behind the low, multi-
banded lake effect snow in northwest flow will continue into today.
Small craft advisory conditions continue on Lake Ontario with gales
continuing over Lake Erie early this morning.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Storm Warning until 7 PM EST this evening for
     NYZ003>008.
     Winter Weather Advisory until 1 PM EST this afternoon for
     NYZ001-002-010-011-013-014-021.
     Lake Effect Snow Warning until 7 PM EST this evening for
     NYZ012-019-020-085.
MARINE...Gale Warning until 4 AM EST early this morning for LEZ040-041.
         Small Craft Advisory until 1 AM EST Thursday for LEZ020.
         Small Craft Advisory until 4 AM EST Thursday for
         LOZ042-043.
         Small Craft Advisory until 7 PM EST Thursday for LOZ044-
         045.

&&

$$

SYNOPSIS...SMITH/ZAFF
NEAR TERM...RSH/SMITH/ZAFF
SHORT TERM...HITCHCOCK
LONG TERM...CHURCH
AVIATION...RSH/SMITH
MARINE...SMITH/ZAFF



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