Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 121902
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
202 PM EST Tue Dec 12 2017

.SYNOPSIS...
A cold northwesterly flow will result in lake effect snow and
blowing snow across the region overnight and into Wednesday.  A
short break is possible late Wednesday before another weak system
moves into the region Wednesday night.  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 WEDNESDAY/...
A deepening surface low continues to move northeast into New England
as an anomalously deep upper level trough plows into the lower Great
Lakes region. Behind the low, lake effect is quickly filling in
behind the synoptic system with multi-bands of lake effect seen
throughout the Great Lakes.

Off Lake Erie...As is often the case in northwest flow, there are a
few stronger bands within the multiband setup.  The strongest area
currently appears to off Lake Huron.  This area should develop a
connection to Lake Erie with some stronger bands moving southward
this evening across the Chautauqua Ridge and then toward or over the
PA border, but with accumulating snow showers on either side of the
strongest area.  The bands should begin to migrate slowly back north
in a weakening state on Wednesday as the next system approaches.
Lake Effect Warnings will remain in place.

The Niagara Frontier should fair better than areas to the south, but
there will still be plenty of multibands overnight plus a
contribution from an arctic boundary dropping south from central
Ontario overnight.  In addition, there will be plenty of blowing
snow to warrant the continuation of a winter advisory into
Wednesday.

Resulting (additional) snow accumulations through Wednesday will
vary substantially from location to location due to transitory
banding, but here are a few areas of interest:
* Inland Chautauqua County:  Highest amounts - over a foot.
* Buffalo area Southtowns:  around or below the 6inch range.
* Other higher terrain...:  4-8 inches.
* Niagara Frontier.......:  1-4 inches.
* Allegany...............:  T-4 inches.

East of Lake Ontario, westerly flow should allow for a potential
short-lived by strong lake band late this afternoon/early evening
with a focus on Oswego County.  Some shore banding is possible too,
but this could be fairly significant in terms of blowing snow and
snow rates exceeding 2"/hr in places.  Later tonight, an arctic
boundary should allow this band to sink south.  12Z models and
hourly HRRR runs continue to show this boundary moving across the
Lake Ontario shoreline around/after midnight with a mesolow on the
west side.  Have yet to see it show up on observations, but it`s
worth watching the Georgian Bay for development later this
afternoon.  Once this moves through, expect multibands on an NW flow
primarily affecting Wayne east through Oswego County into Wed AM. A
connection to the Georgian Bay may continue new band formation
across the shoreline Wed - first over Niagara County, then east to
Wayne County be the end of the day.

Like Erie, resulting (additional) snow accumulations through
Wednesday will vary substantially from location to location due to
transitory banding, but here are a few areas of interest:

* Shorelines west of Rochester: 1-5 inches
* Rochester Area..............: 4-10 -   highest E, less W.
* Wayne to Oswego.............: Possibly a foot overnight.
* Tug Hill Plateau............: 6-12 highest south.
* Watertown...................: Highly variable, but in general 3-5.

&&

.SHORT TERM /WEDNESDAY NIGHT 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 MONDAY/...
Cold and active pattern will persist into Saturday as
several more lower amplitude shortwaves progress through the
longwave trough in place across the eastern CONUS. The result will
be additional snow shower chances.

A deamplifying flow pattern will bring in some slightly milder air
by Sunday and Monday, but will also open the door for stronger
pacific energy to bring a more widespread/heavier, possibly mixed
precipitation maker through Great Lakes Sunday. Models are all over
the place at this time range resulting in a low confidence forecast
beyond Saturday.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
A deepening surface low continues to move northeast into New England
as an anomalously deep upper level trough plows into the lower Great
Lakes region. Behind the low, lake effect is quickly filling in
behind the synoptic system with multi-bands of lake effect seen
throughout the Great Lakes. In terms of flight conditions...general
MVFR/IFR area expected, with IFR within lake effect bands.

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 into New England
as an anomalously deep upper level trough plows into the lower Great
Lakes region. Behind the low, lake effect is quickly filling in
behind the synoptic system with multi-bands of lake effect seen
throughout the Great Lakes.  In general, expect a northwest flow
through at least Wednesday with small craft advisory conditions and
some brief gales over Lake Erie this evening.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Storm Warning until 7 PM EST Wednesday for NYZ003>008.
     Winter Weather Advisory until 1 PM EST Wednesday for NYZ001-
     002-010-011-013-014-021.
     Lake Effect Snow Warning until 7 PM EST Wednesday for NYZ012-
     019-020-085.
MARINE...Small Craft Advisory until 4 PM EST this afternoon for LEZ040-
         041.
         Gale Warning until 4 AM EST Wednesday 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...ZAFF
NEAR TERM...ZAFF
SHORT TERM...HITCHCOCK
LONG TERM...TMA
AVIATION...ZAFF
MARINE...ZAFF


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