Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 080604
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
104 AM EST Thu Dec 8 2016

.SYNOPSIS...
Much colder air will filter in tonight and Thursday and allow lake
effect snow to develop east of the lakes. Lake effect snow will then
intensify later Thursday before becoming oriented southeast of the
lakes Thursday night through Saturday as winds become northwest.
Lake effect snow will finally begin to diminish later Saturday. An
area of low pressure will then move through the Great Lakes Sunday
and Monday and may produce a general snow for much of the region.

&&

.NEAR TERM /THROUGH TODAY/...
Radars over WNY and NCNY indicate a narrow band of lake effect
precipitation generating NE of both lakes. Activity, mainly in the
form of snow but may have some light rain initially, is more
pronounced off Lake Ontario, while Lake Erie is generally more just
flurries of snow for right now. These bands will slowly increase in
strength as lake induced equilibrium levels begin to rise early this
morning. However activity will remain weak to moderate as a layer of
dry mid level air flows over the Lower Great Lakes, which will
offset the increasing lake induced instability to some extent. This
will likely delay the development of a lake response to some extent
and also force the lake bands to be weaker.

Off Lake Erie, this will develop over the southern half of the
Buffalo Metro area to western Genesee County late tonight, before
settling across the Buffalo southtowns in the morning. This may
produce 1-2 inches of accumulation as it does so, with some minor
impacts possible for the morning commute. Off Lake Ontario, expect
lake effect to develop near Watertown and Carthage late tonight and
continue into Thursday morning, again with minor 1-3 inch amounts
possible through the morning with some minor impact to the morning
drive. Precip may initially develop as some light drizzle for the
first few hours if the lake bands develop early enough, but after
4AM everything should change to snow as cold air deepens and the
dendritic crystal growth zone becomes available to the lake bands.

This impactful lake snow event will intensify Thursday as
instability increases under a rising cap. The flow will steadily
veer from 250 to 270 degrees during the course of Thursday as the
lake effect plume of snow develops. This will allow the plume of
moderate to heavy lake snow to settle across southern Erie county
and northern portions of the western Southern Tier, where snowfall
rates will increase to 1 to 2 inches per hour...partially due to
the enhanced orographic lift. Meanwhile off Lake Ontario...a 240
to 250 flow will support lake snows over Jefferson and the
northern half of Lewis County Thursday morning. As in the case of
the activity off Lk Erie...winds will veer to 270 during the
afternoon. The plume of moderate to heavy lake snow will push
south across the Tug Hill in the process. Again...snowfall rates
will increase during this southward push...largely due to
increased fetch and also from orographic lift from the Tug.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/...
...Significant lake effect snow event to impact areas east and
southeast of Lake Erie and Lake Ontario into the weekend...

Impactful lake effect snow event will be well underway as we begin
Thursday night, continuing right into Saturday off both Lake Erie
and Lake Ontario. Instability will still be quite impressive with
lake induced equilibrium levels near 17k feet and lake induced CAPES
near 700 j/kg. Latest model data suggesting that a band of heavy
snow with snowfall rates of at least 2 to 3 inches per hour to be
ongoing on a general westerly low level flow. This will maintain
focus of the Lake Erie snows from roughly Angola to Bliss on the
northern end down across central portions of Chautauqua and
Cattaraugus counties, and the focus of the Lake Ontario snows
across the Tug Hill, just to the south of Watertown and just to
the north of Parish.

As we move through Thursday night, the passage of a surface trough
across the Lower Great Lakes will veer the low level flow to a more
northwest direction. Model profiles suggesting some drop off to
instability levels, likely resulting in diminishing snowfall
intensity, but still could easily snowfall rates of at least an inch
per hour. Despite the veering flow, the focus for the Lake Erie
snows will remain over the Western Southern Tier, particularly
Chautauqua and Cattaraugus counties. The veering flow will push the
Lake Ontario snows further south and off the Tug Hill. This will
place the lake snows across Oswego county. Due to the expected
snowfall rates during the Thursday night time frame, overnight
snowfall amounts are forecast to average a foot along and within 20
miles east of the Chautauqua Ridge, and across the Tug Hill Plateau
region.

Friday and Friday night, nearly all guidance maintaining a
persistent 300-310 flow. This will keep widespread accumulating lake
snows in place southeast of both lakes. The lake band will likely
take on a more multiple band configuration making exact placement
for the heaviest snows a bit more difficult. Although instability is
not quite as impressive as Thursday and Thursday night, profiles
still showing lake induced equilibrium levels around 12k feet and
lake induced capes near 600 j/kg. Upstream connection will likely
become an important element in the development of the more intense
lake bands. Latest NAM and GFS both showing significant upstream
lake contribution to the activity off Lake Erie, but the NAM showing
a fair amount of dry air moving in with limited upstream connection
for Lake Ontario. Snowfall rates should continue in at least the 1
to 2 inch per hour range due to the likely upstream contribution
off Lake Erie, with the degree of organized lake activity off
Lake Ontario a bit more in question. Another foot of snow could
easily accumulate during this 24 hour period focusing on the
Chautauqua Ridge off Lake Erie. The Wayne to Oswego county
corridor off Lake Ontario should have the best chances to see
heavier lake bands, particularly Oswego county. Confidence for
Lake Ontario lake snows in this northwest flow regime is still a
bit low at this stage, therefore will maintain a lake effect snow
watch for the Monroe to Northern Cayuga county corridor.

By the time we reach mid day Saturday, the lake snows should be
steadily weakening off both lakes as high pressure and drier air
build into the region, and as shear increases under the advancing
ridge. A general backing of the low level flow will probably still
send the remnants of these bands back north across the Buffalo and
Watertown areas Saturday afternoon and evening, before these die out
altogether Saturday night as the low level flow becomes too
southerly.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
Just as many are finishing clearing snow from our latest extended
lake effect snow event, we will likely be looking at another round
of wintry weather late Sunday into Sunday night possibly lingering
into Monday morning. Following this there will be chances for more
lake effect snow as a much colder arctic sourced airmass dives south
into 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 next dose of wintry weather following this weeks lake effect
will be associated with a synoptic low that 12z models are now in
much better agreement with regards to the track. Both GFS and EC
are now showing the track to be just to the northwest of Buffalo.
The GFS is much weaker and faster with a 1012ish low center passing
Sunday night while the ECMWF is much stronger and slower showing a
sub 980mb low tracking near western NY on Monday. The EC scenario
would bring a much stronger wind field with potential for very gusty
winds on Monday. The stronger winds would also advect warmer air
aloft northward leading to a better possibility for mixed precip.
The highest confidence is in using a blend of both solutions with
likely POPs for Sunday night and chance POPs Sunday ahead of the
system. Temperatures were also blended at this range which leads to
p-type of snow during the overnight periods and some mixed rain/snow
especially at lower elevations and closer to the lakeshore during
the day Sunday.

This storm will lead in a deep sub-500dm closed low that will shift
to just north of the Great Lakes by next week. This closed low
contains a modified airmass with origins from the polar vortex.
850mb temps dropping to around -20c by mid next week will actually be
cooler then this current weeks 850mb temps. This colder arctic blast
across the Great Lakes looks to bring at least a medium chance of
more lake effect snows Tuesday and potentially Wednesday as long as
there will be sufficient background moisture and lift which latest
models are leading on to. We will have to closely monitor this
situation. Aside from the potential for more lake snows, we are
starting to look 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.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
For the 06Z TAFs generally VFR flight conditions were found across
the TAF sites. A band of lake effect precipitation is developing
northeast of both Great Lakes this early morning, and this weak band
of precipitation may bring some MVFR flight conditions to KBUF/KART
this morning.

Through the day a moderate band of lake effect snow will likely lie
just to the south of KBUF/KART. Flight conditions will be within the
IFR/MVFR range within these bands of snow.

Winds will veer some this afternoon within a cold air advection
regime, and these veering winds will send a now moderate to heavy
plume of lake effect snow across the Southern Tier, including the
KJHW terminal...and off Lake Ontario across the southern Tug Hill
region. Flight conditions tonight will likely range in the LIFR/IFR
range.

Intense bands of lake effect snow tonight may also produce some
thunder off both lakes, with any TAF site impacted being the KJHW
terminal. A surface trough will cross the TAF region, beginning
around 06Z near KART...and this surface trough will slide the lake
bands farther southward off Lake Ontario late tonight.

Outlook...

Friday through 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.

&&

.MARINE...
Small craft conditions will continue into tonight right through
Saturday on both lakes Erie and Ontario as low pressure moves very
slowly east across Quebec, producing moderate west to northwest
winds on the Lower Great Lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lake Effect Snow Warning from 6 AM this morning to 6 AM EST
     Friday for NYZ007-008.
     Lake Effect Snow Warning from 6 AM this morning to 6 AM EST
     Saturday for NYZ006-012-019-020-085.
     Lake Effect Snow Watch from this evening through late Friday
     night for NYZ003>005.
MARINE...Small Craft Advisory until 7 PM EST Friday for LEZ040-041.
         Small Craft Advisory until 10 PM EST this evening for
         LEZ020.
         Small Craft Advisory until 7 AM EST Saturday for
         LOZ042>045.

&&

$$

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



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