Area Forecast Discussion
Issued by NWS Buffalo, NY

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844
FXUS61 KBUF 072155
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
455 PM EST Wed Dec 7 2016

.SYNOPSIS...
Much colder air will filter in tonight such that scattered light
lake effect precipitation today and this evening east of the lakes
will increase in intensity on Thursday, while transitioning over to
snow. Bands of lake effect snow, will become established by mid-day
Thursday east and southeast of the lakes, producing heavy snow
through Saturday.

&&

.NEAR TERM /THROUGH THURSDAY/...
For today and into tonight, much of the region will be seeing the
relative calm before the significant lake effect event that will
ramp up on Thursday. Temperatures aloft this morning (-6 to -7C) are
already cool enough to support the lake effect cloudiness seen on
visible satellite imagery over Lake Erie and Ontario. However, the
capping inversion level remains below 4kft, along with a very dry
slot of air above that through the dendritic growth zone. This will
continue through this afternoon and overnight tonight, as the upper
level low and associated synoptic moisture remain to our west over
the upper Great Lakes. That means for this afternoon and evening,
would not rule out some scattered areas of sprinkles or drizzle
under the lake effect clouds northeast of the lakes, as all the
moisture will remain below the dendritic growth zone and lake
equilibrium levels remain very low.

Overnight tonight and into early Thursday morning, have backed off
the development a plume of lake effect snow into the Buffalo and
Watertown areas on the southwesterly flow. The primary reason for a
more delayed start to the accumulating snow is due to latest model
guidance delaying the arrival of more significant synoptic moisture.
Thus while equilibrium levels rise, there won`t be much background
moisture or synoptic lift to excite the lake effect snow bands in
the early morning hours. Thus expect continued drizzle/sprinkles or
light snow showers leading up to the morning commute. Thus any
potential impacts to the morning commute Thursday would be limited
to an areas were some slick spots can form if temperatures become
cold enough for drizzle to freeze, however that is a very low
confidence treat at this point. This also means very little to no
snow accumulation for much of the Buffalo metro area, with the
exception of the far southtowns, through Saturday.

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 Ski Country, 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 /22Z WEDNESDAY THROUGH MONDAY/...
Lake effect cloudiness will persist east and northeast of lake Erie
and Ontario (near KART, KBUF, and KIAG) this afternoon through
overnight tonight. Cannot rule out some areas of drizzle this
afternoon and and overnight tonight under these lake clouds, however
the main lake effect snow threat will hold off until mid-morning
Thursday, and being shifting southward away from KBUF/KART, and
toward KJHW/KFZY. Thus expect mainly VFR to MVFR conditions to
persist at the TAF sites. MVFR becoming IFR conditions will develop
east of the lakes on Thursday, possibly clipping KART mid-day
Thursday, and then moving into KJHW by Thursday afternoon.

Outlook...

Thursday night through Saturday...IFR in lake effect snow east and
southeast of the lakes. Occasional snow showers with more brief IFR
elsewhere.
Sunday and Monday...MVFR/IFR in widespread light snow.

&&

.MARINE...
Behind a cold front, westerly flow is increasing across the lakes
today. This will result in small craft advisory worthy winds up to
25 knots on the lakes today, with gusty winds also across portions
of the major rivers.

Small craft conditions will then continue into the weekend 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 this evening for LEZ020.
         Small Craft Advisory until 7 PM EST Friday for LEZ040-041.
         Small Craft Advisory until 7 AM EST Saturday for
         LOZ042>045.
         Small Craft Advisory until 7 PM EST this evening for
         SLZ022.

&&

$$

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



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