Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 090556
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1256 AM EST Fri Dec 9 2016

.SYNOPSIS...
Cold air will cross the Eastern Great Lakes through Saturday,
producing bands of lake effect snow that will oscillate along the
southeast shores of the Lakes Erie and Ontario. Accumulations of
snow may be measured in feet on the higher elevations to the east of
the lakes, before diminishing in intensity later Saturday. An area
of low pressure will then move through the Great Lakes region Sunday
and Monday, producing a general snow for much of the region.

&&

.NEAR TERM /THROUGH TODAY/...
Will drop the Lake Effect Snow Warning for Jefferson and Lewis Cos.
with this update. A surface trough continues to drop southward this
morning across Lake Ontario, pushing the Lake effect snow southward
towards the southern shoreline and points inland. A few upslope snow
showers will linger across Lewis Co. this early morning, with just
another inch or two of accumulation.

The Lake Erie band has weakened substantially possibly in response
to increasing shear with the passage of a mid level shortwave, and
also in response to a changing low level wind field. The snow should
become better organized again after midnight as the boundary layer
flow becomes better aligned again from the northwest.

Through the night, a surface trough connected to the surface low
tracking east across Quebec will drop across southern Canada and
towards the Eastern Great Lakes. This trough will not only increase
the low level lift and snowfall rates, but also begin to shove the
lake effect snow southward.

Off Lake Ontario overnight into Friday...

The warm waters of Lake Ontario may delay the passage of the trough
some through the night, but by dawn tomorrow morning northwest flow
will be well established. During the trough passage, expect much of
the east/west oriented band to be captured and moved onshore bodily,
with a burst of snow moving south along the south shore of the lake
from the Rochester area to Oswego County during the wee hours of the
morning. Following this, multiple bands will likely develop in the
northwest flow regime behind the trough. Snowfall rates will still
be 1-3 inches per hour until the trough passage, then the lake
effect snow will weaken significantly.

On Friday a push of drier mid level air, and a shorter northwest
fetch will greatly limit the intensity of lake effect snow southeast
of the lake. Expect relatively light lake effect snow showers to
continue from the Rochester area east to Oswego County, with only 1-
3 inches of accumulation in the more persistent bands. There will
also be a Georgian Bay band meandering around, which may bring an
inch or so of accumulation to the Niagara Frontier west of Rochester
and northeast of Buffalo.

Off Lake Erie overnight into Friday...

The lake snow band east of Lake Erie will reorient to the new
northwesterly wind overnight, forcing the stronger band of snow to
shift southwest across Chautauqua and western Cattaraugus counties,
with weaker multiple bands developing in its wake. There will also
be a dynamic upstream connection developing late tonight to the snow
off southern Lake Huron to seed the band off Lake Erie. This
upstream connection will be the main focus for the heaviest snowfall
rates for Friday. Expect this to drift into far western Chautauqua
County near Findlay Lake during the morning and possibly into Erie
County PA for a time, before moving back east and into Chautauqua
County later in the afternoon. This band with an upstream connection
may still produce 1-2 inch per hour snowfall rates. Otherwise across
the rest of the western Southern Tier, weaker multiple bands and
weaker upslope flow will bring occasional light to moderate snow
showers.

There will also be a gusty wind this period, especially around the
edges of the lake effect snow bands tonight. Wind gusts may near 30
to 35 mph that will bring additional blowing and drifting to the
snows.

Air temperatures will be seasonable this period...with overnight
lows remaining in the 20s. High temperatures on Friday will not be
much warmer with readings in the upper 20s to the lower 30s.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
A 290 to 300 degrees low level flow should be in place Friday night,
continuing to focus the heavier lake snows into the western Southern
Tier off Lake Erie and into Northern Wayne and Cayuga counties,
perhaps clipping Northern Monroe county. Over-lake instability
continues to be impressive with lake induced CAPES around 700 j/kg
and lake equilibrium levels between 10k-15k feet. This suggest that
snowfall rates will continue to be in excess of an inch per hour.
Additional accumulations Friday night could be significant within
the warning areas.

Steering winds will gradually back late Friday night and Saturday as
the upper level trough gradually weakens. This will bring low
level winds from 290/300 degrees to 240/250 by Saturday
afternoon/evening. Expect the band off Lake Erie to remain organized
as it briefly focuses on Southern Erie county before lifting north
across the Buffalo metro area. Amounts will be limited due to the
transitory nature of the band, but depending on how intense the band
it, it is possible that several inches of snow could push into the
Buffalo metro area during the day Saturday.

By Saturday night, the flow should continue to back to more
southerly which would push whatever lake effect snow to our west.
A similar story will play out off Lake Ontario, with lake effect
snows lifting northward.

Sunday and Sunday night, the above mentioned backing flow is
expected ahead of the next system expected to arrive during this
time period. Consensus model blend would suggest that isentropically
driven snow arrives very late Saturday night or early Sunday,
continuing through into Sunday night. This system does have a tap
into Gulf moisture, with profiles showing deep moisture through the
dendritic growth zone which would help snowfall rates. It is very
possible that several inches of widespread snow will fall Sunday
into Sunday night with another possible winter weather headline
event looming.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
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 /06Z FRIDAY THROUGH TUESDAY/...
For the 06Z TAFs bands of lake effect snow continue with poor flight
conditions. Off Lake Erie the band of snow will likely linger the
longest over KJHW where a northwest flow will maintain IFR or lower
flight conditions into the late morning hours. Off Lake Ontario, a
southward push to the lake snows will bring a period of IFR flight
conditions to KROC early in the TAF period before activity weakens
and thins through the dawn hours, and thereafter.

Today winds will become northerly, possibly bringing the LES to the
west of KJHW, while weak multi banded snow bands will be possible
south of Lake ONtario, including the KROC airfield, and possibly
KIAG.

This evening winds will begin to back some as surface high pressure
creeps closer to the region from the Central Plains. It will
continue to remain cold enough, and moist enough for lake effect
snow with upstream connections to lake Huron and Georgian Bay
bringing narrow bands of moderate to heavy snow towards KJHW and
KROC through Friday night. Certainty this far out will be medium at
best as the wind fields remain light, and any minor fluctuation in
wind direction will change the course of both upstream and over the
nearby lake snowbands.

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.

&&

.MARINE...
High end small craft advisory conditions will continue right through
Saturday on both lakes Erie and Ontario as low pressure moves very
slowly east across Quebec, producing moderate to strong west to
northwest winds on the Lower Great Lakes. Winds will be strongest on
Lake Ontario, reaching a solid 30 knots tonight on the central and
eastern waters.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lake Effect Snow Warning until 6 AM EST Saturday for NYZ006-
     012-019-020-085.
     Lake Effect Snow Warning until 6 AM EST Saturday for NYZ004-
     005.
     Lake Effect Snow Advisory until 6 AM EST Saturday for NYZ003.
     Lake Effect Snow Advisory until 10 AM EST this morning for
     NYZ021.
MARINE...Small Craft Advisory until 7 PM EST this evening for LEZ040-
         041.
         Small Craft Advisory until 4 AM EST early this morning for
         LEZ020.
         Small Craft Advisory until 7 AM EST Saturday for
         LOZ042>045.

&&

$$

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



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