Area Forecast Discussion
Issued by NWS Buffalo, NY

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028
FXUS61 KBUF 091840
AFDBUF

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

.SYNOPSIS...
Cold air will continue to flow southeastward across the Great Lakes
region today, bringing lake effect snow mainly off Lake Erie
today, with scattered activity off Lake Ontario. A more pronounced
band of snow is expected to form tonight as upstream lakes bring
additional moisture across the eastern Great Lakes, with a band of
lake effect snow across southwest New York State, and another
band south of Lake Ontario across eastern Orleans to western
Oswego Counties. An 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 TONIGHT/...
Have made some changes to the forecast concerning the lake effect
snow to the south of Lake Ontario. Will upgrade the Lake Snow
Advisory for Monroe County to a Warning, and add Orleans County to
the list with a Lake Snow Advisory. Although the lake snow has
currently extended to the west as far as Niagara, Northern Erie and
Northern Genesee counties, this portion of the snow band has broken
off and will dissipate. The upstream connection from Georgian Bay
will re-establish a stronger lake snow band from Monroe County,
eastward to Northern Cayuga County, requiring an upgrade to a Lake
Snow Warning for Monroe County through tonight. The Lake Ontario
snow band should be at it strongest during the late afternoon today,
through tonight and then start to show indications of moving to the
north as the next synoptic system approaches from the west.

Off Lake Erie, there will likely be an upstream connection to Lake
Huron, such that even the veering winds off Lake Erie will still
maintain some structure to a band of snow, with the snow inching
westward through the day. There may be a time this early afternoon
that the lake effect snow almost leaves the state, falling over NW
PA before winds begin to back in response to a surface high pressure
bulging across the Midwest and Tennessee Valley that will bring the
lake effect snow back across Chautauqua County this afternoon and
evening. Snowfall totals today will near an additional half a foot
over the western part of the County, with much less over eastern
parts of the county, and Cattaraugus. High temperatures today
will likely remain below freezing for much of the region, with
highs in the mid to upper 20s.

The North Country will likely remain dry through this period under
the northwest flow. There may even be a bit of clearing tonight
across inland Jefferson and Lewis Counties. If this were to occur,
overnight lows here may drop well into the lower teens, with
possible upper single digits across the colder spots. South of Lake
Ontario where clouds will be common, overnight lows tonight will be
in the 20s.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
The ingredients for lake effect snow will remain in place on
Saturday with more than ample lake induced instability (850mb temps
about -14C) and lake equilibrium levels between 10k-15k feet. The
main forecast challenge will be winds, since the flow will be a
rather light one, especially across Lake Ontario. Model consensus
brings a weak shortwave across the region during the day, which will
enhance moisture and snowfall rates with its passage. 00Z guidance
now maintains a westerly flow off Lake Erie several hours longer,
lasting through the day. This will maintain lake effect snow across
the Western Southern Tier longer, prompting the Lake Effect Snow
Warning to be extended through the day for Chautauqua and
Cattaraugus counties. This also will keep lake effect snow south of
the Buffalo metro area during the daytime on Saturday.

Off Lake Ontario, the flow will be much lighter, with mesoscale
guidance suggesting a meso-low may stall across Lake Ontario. If
this does drift southeast into the Eastern Lake Ontario region then
it may require advisories with several inches of snow possible. For
now, there is not enough forecast confidence to issue headlines for
this feature yet.

By Saturday night, the flow should to back to more southerly which
would lift the Lake Erie snow band across the Buffalo metro area
Saturday evening. The band will be moving quickly so it will
probably be sub-advisory with only an inch or two accumulation.
Similarly, the more southerly flow will push lake snows north of
Lake Ontario by late Saturday night.

Sunday and Sunday night, a synoptic system will approach the region,
bringing widespread precipitation to all areas. The surface low will
still be across the midwestern states on Sunday however diffuse mid-
level warm air advection will extend northeast of the system and
spread into Western New York during the day. This will strengthen
Sunday night, with the region also in a favorable jet-quadrant for
enhanced lift. Model consensus is in good agreement, supporting
categorical pops by Sunday night and into Monday.

Snowfall rates should be modest with this system, with storm totals
much less impressive than the ongoing lake effect event.  However
because it is synoptic all areas should get at least some snow, and
totals may reach advisory amounts with several inches of snow in
many areas. Guidance still disagrees on the track of the low. Most
guidance brings a weak surface low across or just north of the area
which would likely result in some mixed precipiation late Sunday
night or Monday south of I-90. This would hold amounts down some in
these areas, but still could hinder travel.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
There continues to be a high likelihood of wintry weather persisting
into next week as a much colder arctic sourced airmass is forecast
to dive south towards the Great Lakes region. This arctic air may
bring the coldest temperatures that we have seen this season by mid
to late next week.

The 08/12z GFS and EC continue to show potential for a closed
surface low tracking across the eastern Great Lakes Monday but
remain in some disagreement with regards to the strength of this
low. These models have flip-flopped when compared to 07/12z runs
with the GFS now the deeper low near 992mb tracking just to the
northwest of Buffalo while the EC is weaker than yesterday only
showing a 1007mb low tracking along the NY/PA state line. Have
included likely POPs for Monday as both models do show sufficient
lift and moisture but the strength of the winds will end up coming
down to the exact depth of the low. The deeper GFS scenario would
bring a much stronger wind field with potential for very gusty winds.

This storm will lead in a deep sub-500dm closed low shifting south
out of the Arctic to somewhere between the Great Lakes and James Bay
by mid next week. The models are showing separation in the placement
of this mid level low which has origins from near the pole. This
disagreement is keeping a lower confidence in exactly how cold of an
airmass reaches western and central NY mid to late week. The GFS is
showing 850mb temps in the -20s C reaching our forecast area while
the EC only shows negative teens C. While both airmasses could
support lake effect snows if enough background moisture is
available, the colder airmass would lead to steeper lapse rates and
more intense snow bands. Have continued medium chance POPs for lake
snows east of the lakes Tuesday into Thursday. Aside from the
potential for more lake snows, we are looking at a very cold period
for much of next week. Cold cyclonic flow may contribute to the
coldest temps we have seen this season which could mean highs only
in the teens to mid 20s by Wednesday and Thursday.

&&

.AVIATION /18Z 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 Vayuga 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 today and tonight. Winds near 30 knots early will diminish
through the day today as surface low across eastern Canada pushes
farther eastward over the Atlantic waters. 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 4 AM EST Sunday for LEZ040-041.
         Small Craft Advisory until 7 AM EST Saturday for
         LOZ042>045.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...THOMAS/WCH
SHORT TERM...APFFEL
LONG TERM...SMITH
AVIATION...WCH
MARINE...THOMAS



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