Area Forecast Discussion
Issued by NWS Buffalo, NY

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839
FXUS61 KBUF 080005
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
705 PM EST Wed Dec 7 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 THURSDAY/...
Radar imagery is clear of any lake response so far this evening with
just a plume of lake effect clouds noted in surface observations and
IR satellite data northeast of the lakes. This will continue to be
the case through the evening with shallow inversion heights below 5k
feet only supporting lake effect clouds.

Overnight tonight and into early Thursday morning, it continues to
be a tricky forecast in regards to when lake effect will begin to
develop. Lake induced equilibrium levels will rise rapidly after 06Z
as the cold air deepens, and reach over 10K feet by daybreak. Both
the NAM and GFS however forecast a layer of dry mid level air late
tonight 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 initially when the do form. Nonetheless,
with the rapidly rising equilibrium levels and some development
noted in most of the high resolution guidance such as the HRRR,
Canadian GEM, and our workstation WRF, it appears likely that some
lake response should develop by late tonight.

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 2 to 3 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 /THURSDAY NIGHT 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 Hamburg to Warsaw 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 Fulton.

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 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 /00Z THURSDAY THROUGH MONDAY/...
Lake effect cloudiness will persist east and northeast of Lake Erie
and Ontario (near KART, KBUF) through tonight with areas of MVFR
CIGS. Lake effect snow will begin to develop east and northeast of
the lakes late tonight near KBUF and KART. This may begin as some
drizzle initially, but as cold air deepens precip will change to all
snow by 09Z.

Winds will become more westerly Thursday morning, aiming most of the
Lake Erie lake effect snow east of the lake and between KBUF and
KJHW. Expect local IFR conditions within the heavier bands of snow.
East of Lake Ontario lake effect snow will continue near KART
through midday before the band moves to the Tug Hill region for the
afternoon. IFR will be common within the heavier portion of this
band.

Outside of lake effect areas mainly VFR conditions will prevail
tonight and Thursday.

Outlook...

Thursday night 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 Thursday to 6 AM EST Friday
     for NYZ007-008.
     Lake Effect Snow Warning from 6 AM Thursday to 6 AM EST
     Saturday for NYZ006-012-019-020-085.
     Lake Effect Snow Watch from Thursday 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 Thursday for LEZ020.
         Small Craft Advisory until 7 AM EST Saturday for
         LOZ042>045.

&&

$$

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



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