Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 030256
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
956 PM EST Fri Dec 2 2016

.SYNOPSIS...
Cold air flowing across the Lower Great Lakes will result in lake
effect rain and snow showers southeast of Lakes Erie and Ontario
overnight. These will slowly fall apart Saturday and Sunday as
high pressure builds across New York State. There will be a few
periods of rain and snow showers through mid next week before much
colder air arrives late week possibly kicking off significant lake
snows.

&&

.NEAR TERM /THROUGH SATURDAY/...
Surface analysis shows a tight pressure gradient over New York State
late this evening between low pressure over northern Maine and high
pressure expanding into the Ohio Valley. A northwest flow of -5C
850mb flow (per 00z KBUF RAOB) over the eastern Great Lakes continues
to drive multiple bands of weak lake effect showers southeast of
Lakes Erie and Ontario. Regional radars now show the most dominant
band over the western Southern Tier off Lake Erie. Temperatures are
marginal for rain vs snow. Rain continues to be observed at the
lowest elevations near the lakes with snow across the higher terrain
and a mix of rain/snow in between. Only expect an inch or so
additional accumulation of snow across the higher terrain of the
western Southern Tier with less than an inch across the higher
terrain of the Finger Lakes and southern Tug Hill.

Saturday, moisture in the lower levels, and within the favorable
snow growth zone will begin to wane, and we should see a
diminishment to lake effect precipitation, which will be southeast
of the lakes on a northwest flow. Temperatures continue to be
marginal, with a mix of rain and snow possible although could also
see just some drizzle as linger moisture will be confined to beneath
the prime snow growth zone. In areas where snow does fall, perhaps
an inch or so would be possible across the western So. Tier hills
tops and the Tug Hill region.

Temperatures tonight will drop to around freezing across higher
terrain, while across the lake plain lows will remain in the mid
30s. Saturday highs will rebound slightly, back into the mid 30s to
lower 40s.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Nuisance lingering lake effect showers will wind down Saturday night
into early Sunday morning. The large surface high will advance to
the east across the Lower Great Lakes Saturday night. This will
further strengthen the lowering subsidence based cap and essentially
squash the remaining lake effect rain and limited snow showers.
Otherwise...it will be partly to mostly cloudy and uneventful.

On Sunday...the axis of the surface high will cross our forecast
area. We should experience at least some breaks of sunshine...
although temperatures will be similar to those of Saturday with
afternoon mercury readings in the 30s to lower 40s.

Conditions will deteriorate Sunday night as a negatively tilted
trough...in the process of shearing out...will sweep northeast
across all of the Great Lakes region. While there will be some
lift provided by a diffluent upper level flow...the overall dynamics
with this feature do not look very impressive. Nonetheless, expect
light precipitation to overspread the region, mainly in the form of
snow. A light coating is possible across the lake plains, mainly on
grassy surfaces due to marginal surface temperatures, with up to 1
to 2 inches across the higher terrain where surface temperatures
will remain below freezing.

As the shearing trough pushes away to our northeast on Monday...
drier mid level air will arrive in its wake while ridging will
become re-established over the region. This will encourage the light
snow from the previous night to taper off and end as a mix of rain
and wet snow showers by midday. While not significant...the mixed
showers will linger a bit longer east of both lakes due to a little
lake enhancement. Daytime snow accumulations will be unlikely.

Tuesday will provide a brief break in the weather as high pressure
moves into Quebec, allowing for a mostly dry day. However, the next
approaching shortwave trough in the southwesterly flow will bring
another chance of rain by late in the day Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
A significant pattern change will take place across North America
during the second half of next week, which will deliver much colder
air into the Great Lakes and New England and possibly set the stage
for a significant lake effect snow event.

A parade of strong synoptic systems moving east through the Pacific
wave train will amplify the pattern across the North Pacific through
the weekend. This will in turn force a ridge to develop over western
North America for the second half of next week, allowing a deep
trough to carve out over the Great Lakes. The developing trough will
capture a large piece of cold Canadian air and circulate it through
the Great Lakes region by late next week.

Looking at the details...

Tuesday night a southern stream trough will move quickly through the
Ohio Valley and Northeast States. Warm advection ahead of the trough
will warm the low and mid levels enough to allow much of this to
fall as rain across lower elevations, although some wet snow may mix
in across higher terrain and the North Country. Most of this will
end by Wednesday morning as a dry slot moves into the area, although
a few widely scattered showers cannot be ruled out as a secondary
cold front crosses the area.

Wednesday night through Friday the mid level trough will become
established across the Great Lakes with cold air flooding into the
region. While the large scale pattern has been consistent in model
guidance over the past few days, the synoptic details and timing are
anything but clear with significant run to run differences. The 12Z
GFS remains faster in bringing the cold air in, with lake effect
developing east of the lakes as early as Wednesday Night. The ECMWF
is slower, bringing a wave of low pressure northward along the east
coast Thursday. This may produce some light wet snow or rain across
our region, and would delay any lake effect until Thursday night, a
full 24 hours later than the GFS. The ECMWF solution would also
result in a more northwest flow regime by the time the air is cold
enough to support lake effect.

The significant model differences on the synoptic scale evolution,
and the fact that this event is still a week away, still bring
plenty of uncertainty with respect to placement and intensity of
lake effect snow. That said, the upper air pattern supports the
potential for a significant event. CIPS extended analogs based on
the GEFS ensembles are returning a number of dates which had
significant lake effect snow downwind of Lakes Erie and Ontario, and
the pattern matches closely to some of our own analogs for
significant events developed through local research at NWS BUF. With
that in mind we have outlined the potential in the HWO. Stay tuned...

&&

.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Multiple bands of lake effect rain/snow continue southeast of Lakes
Erie and Ontario late this evening. A northwest flow which will
persist through tonight will keep KBUF/KIAG/KART generally free of
any precip while KROC and KJHW continue to see periods of rain/snow
and occasional MVFR cigs overnight.

On Saturday, Lake snows will considerably weaken as high pressure
builds over western NY. Despite the weakening lake effect, guidance
continues to indicate lingering low level moisture which will keep
MVFR or low end VFR cigs around much of the day.

Outlook...

Saturday night through Sunday...Mainly VFR with gradually
diminishing lake effect rain/snow showers and attendant areas of
MVFR southeast of the lakes.

Monday...MVFR with a chance of rain and snow showers.

Tuesday and Wednesday...VFR with a chance of mainly rain showers.

&&

.MARINE...
A brisk northwesterly overnight behind a surface trough. Winds will
slowly diminish overnight and Saturday with weak high pressure
building over western NY. Small craft advisories will continue into
Saturday as waves slowly diminish through the day. Fair boating
conditions will be in place Sunday through Tuesday before winds and
waves build again likely to Advisory levels as a cold front crosses
the eastern Great Lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 7 PM EST Saturday for LEZ040-041.
         Small Craft Advisory until 4 AM EST Sunday for
         LOZ043>045.
         Small Craft Advisory until 7 PM EST Saturday for LOZ042.

&&

$$

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



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