Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 092033
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
333 PM EST Fri Dec 9 2016

.SYNOPSIS...
Cold air will continue to flow across the Great Lakes region with
areas of lake effect snow to the south and east of Lakes Erie and
Ontario. These lake snow bands are expected to intensify overnight,
the move to the north as low pressure approaches from the west. This
area of low pressure will then move through the Great Lakes region
Sunday and Monday, producing a general snow, possibly mixed with a
little rain or sleet for much of the region.

&&

.NEAR TERM /THROUGH SATURDAY/...
Will continue the Lake Snow Warnings and Advisory through the night
as lake effect snow remains off Lakes Erie and Ontario.

One of the main factors in the persistence and strength of the lake
snow is the connection to lake effect snow plumes from Great Lakes
waters farther upwind of the eastern lakes. We have one plume from
the southern end of Lake Huron crossing the northern tip of Lake
Erie, and inland  to the hills of Chautauqua and Cattaraugus
counties. This nearly continuous area of lake snow is at times
formed as multiple bands or as a single plume, occasionally broken,
but still delivering snow at a rate of a half inch to an inch an
hour. The steady accumulation of snow adds up over time and many
locations within the lake snow bands have received another foot of
snow, or more, just today with more snow expected through the night
and Saturday.

The conditions to the south of Lake Ontario have become more
disrupted as the connection to Georgian Bay broke off earlier today,
but will reform late today and through the night. The area of lake
snow is expected to cross a larger fetch on the lake and come
onshore at Monroe County. Light converging winds and a westerly
shore component will direct the lake band along the shore to the
east and bring the heavier snow to eastern Monroe County, across
Wayne and Northern Cayuga to Southern Oswego County. The intensity
and steady state of the snow plume could drop up to another foot of
snow over central Wayne and Northern Cayuga counties.

Westerly winds across the bulk of Western and Central New York will
keep the flow of snow moving eastward from the lakes. Winds across
the Lake Ontario basin and Northern New York will be light and
variable, producing a zone of convergence along the south shore of
the lake, further enhancing the lake snow band. Winds are expected
to shift to a more southwesterly direction on Saturday night.

Temperatures will drop to the teens and low 20s overnight, with
single number east of Lake Ontario, in areas of clearing skies and
fresh snow. Highs on Saturday will rise to the mid 20s to lower 30s.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
Lingering lake effect snow will continue east of the lakes Saturday
night, and will slowly lift northward toward Buffalo and Watertown
by Sunday morning while weakening and decreasing in inland extent.
While a few more inches of snow accumulation are expect across the
western Southern Tier and Tug Hill region, the weakening snow bands
may only result in an inch or two of snow across the Buffalo and
Water town areas Sunday morning.

Our attention then turns to the widespread snowfall event that is
setting up for Sunday night, which may bring some slow downs to
morning commutes across the region Monday morning. This weather
system evolves out of the low pressure system currently coming on
shore in the Pacific Northwest. The shortwave trough, and
accompanying surface low reflection, will track along the baroclinic
zone across the Great Lakes Sunday night and Monday. Ahead of the
wave and surface low, widespread snowfall will develop in the warm
air advection and along the band of frontogensis, with the region
also in a favorable jet-quadrant for enhanced lift. Model consensus
is in good agreement, supporting 100 PoPs Sunday night.

Model guidance is improving with the track of this system, with more
guidance now pointing to keeping the above freezing air aloft south
of the forecast area, across PA. This means there is a decreasing
chance of a wintry mix of precipitation Sunday night into Monday,
with most of the precipitation falling as all snow Sunday night. With
the track of the surface low still just north and west of the
forecast area, we will see warmer surface temperatures pushing into
the mid 30s during the day Monday. Precipitation will also end from
west to east Monday morning through mid-day as mid and upper level
dry air moves in across the area, which will result in snow ending
and changing over to a light drizzle on Monday. The the increasing
likelihood of all snow Sunday night, snowfall amounts will likely
end up warranting an advisory, with most locations picking up 4 to 6
inches.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
The active and very wintry pattern will continue through the long
term, and even intensify by late next week. Looking at the longwave
pattern, a sharp upper level ridge will build over Alaska early next
week and allow for a period of cross polar flow, with Siberian air
making the trip across the Arctic and into northern Canada. The
Alaskan ridge will remain in place through much of the week and
force a deep longwave trough to develop over central and eastern
North America. A large piece of true arctic air will move south
through the Canadian Prairies and reach the Great Lakes and New
England later next week. This may set the stage for another round of
significant lake effect snow for Thursday and Friday. As the cold
air comes in, another baroclinic wave may bring some widespread
general snow Wednesday.

Looking at the details, on Tuesday and Tuesday night a weak trough
will pass through the Great Lakes and may produce a few light snow
showers of little consequence. There may also be some limited lake
effect snow east of the lakes, but marginal instability will keep
this light.

On Wednesday the longwave trough will begin to dig into the Northern
Plains and Upper Great Lakes. Ahead of the trough, medium range
model guidance develops a baroclinic wave over the Ohio Valley and
Northeast. The GFS and most of it`s ensemble members along with the
Canadian GEM are more aggressive with this, and would produce a
general light to moderate snowfall across the entire area. The 12Z
ECMWF is much weaker with this feature. The ECMWF has shown a good
deal of inconsistency with this system, as previous runs looked more
similar to the current 12Z GFS. With this in mind, went closer to
GFS based guidance with snow likely for Wednesday.

In the wake of this system cold air will flood into the Great Lakes
Thursday and Friday. This will be the coldest air of the season,
with 850mb temps plummeting to -20C or colder. This will translate
into highs in the teens and lows in the single numbers away from the
immediate lakeshores. The deep cold air crossing the lakes and the
overall pattern is suggestive of more significant lake effect snow
downwind of the lakes for Thursday and Friday, however there are
significant differences in wind direction, not to be unexpected
given this is still 6-7 days out.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
Cold air remains across the region with areas of lake effect snow to
the east and south of Lakes Erie and Ontario. Through 18Z on
Saturday, the lake snow bands will be persistent across the Western
Southern Tier and the snows will redevelop and intensify across the
south shore of Lake Ontario.

TAF sites most affected by the snow will be KJHW and KROC. KJHW
will remain in the lake snow band`s influence with MVFR visibilities
degrading to IFR/IFR after 12Z Saturday. KROC starts VFR until the
lake snow connection to Georgian Bay links up with Lake Ontario and
MVFR conditions at 05Z lower to near IFR conditions at 12Z Saturday.
Weather conditions to the east of Rochester will be much worse as
the lake snow moves onshore across Wayne and Cayuga counties. The
remaining TAF sites should stay out of the heavier snow with VFR
ceilings and light snow although there may be periods after 18z
Saturday when conditions degrade as the winds become more
southwesterly and push the snow to the north ahead of an approaching
low pressure system, due to cross the region later in the weekend
and early workweek.

Outlook...

Saturday...IFR in lake effect snow southeast of the lakes.
Occasional snow showers with more brief IFR elsewhere.
Sunday and Monday...MVFR/IFR in widespread light snow.
Tuesday...MVFR with a chance of snow showers.
Wednesday...MVFR/IFR in snow.

&&

.MARINE...
Small craft advisories will remain in place across the Eastern Great
Lakes tonight. Winds will diminish as low pressure across Eastern
Canada pushes farther eastward over the Atlantic waters. Although
winds will fall below small craft advisory levels along the Lake
Ontario shore, and advisories will be dropped there, winds will
again increase Saturday, and will likely continue SCA on Lake Erie
through the night of Saturday.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lake Effect Snow Warning until 6 AM EST Saturday for
     NYZ003>006.
     Lake Effect Snow Advisory until 6 AM EST Saturday for NYZ002.
     Lake Effect Snow Warning until 6 PM EST Saturday for NYZ019-
     020.
MARINE...Small Craft Advisory until 7 AM EST Sunday for LEZ040-041.
         Small Craft Advisory until 4 AM EST Saturday for
         LOZ043>045.
         Small Craft Advisory until 10 PM EST this evening for
         LOZ042.

&&

$$

SYNOPSIS...WCH
NEAR TERM...WCH
SHORT TERM...CHURCH
LONG TERM...HITCHCOCK
AVIATION...WCH
MARINE...WCH



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