Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 140319
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1019 PM EST Wed Dec 13 2017

.SYNOPSIS...
A weak area of low pressure will bring a period of snow to most of
Western New York tonight. Following a brief break mid-day Thursday
another system will bring more lake effect snow to some areas Friday
and Saturday. Meanwhile it will continue to be cold with highs in
the teens Thursday.

&&

.NEAR TERM /THROUGH THURSDAY/...
A clipper low centered over northern Ohio will push east across
Pennsylvania during the overnight. This will generate a general
light snow to the tune of an inch or two for locations south of Lake
Ontario...with as much as four fresh inches of snow across the
Southern Tier where a winter weather advisory is in effect.

The clipper will move away quickly on Thursday, with drier air
behind the system causing lake effect snows to temporarily taper off
during the middle portion of the day. Another shortwave will
approach late in the day with lake snows expected to redevelop near
the Chautauqua ridge and southeast of Lake Ontario centered between
Sodus and Oswego.

Otherwise, temperatures will be much below normal. Even though
clouds and winds will limit radiational cooling tonight, lows will
mainly ranges from the single digits to lower teens. Any clearing
could allow below zero readings across the North Country. Highs on
Thursday will be mainly in the teens, with lower 20s along the
immediate lakeshores.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
Thursday night through Friday lake effect snow will continue
southeast of Lakes Erie and Ontario.

Off Lake Erie...

Lake induced equilibrium levels will be relatively low, at about 8K
feet. This will yield a shallow, but sufficient layer of dendritic
crystal growth. Given the marginal moisture and cloud depth, lake
effect snow should remain rather light in nature. During Thursday
evening it will still be located across the western Southern Tier
with WNW flow. Late Thursday night and Friday morning boundary layer
flow will quickly back to the southwest ahead of the next clipper,
carrying lake effect snow northward across Erie County. This band
will cross Buffalo during the early to mid morning before ending up
in Niagara County by midday. Snowfall amounts will be light, with 1-
3 inches across the western Southern Tier and the Buffalo area.

Off Lake Ontario...

A band of lake effect snow over northern Cayuga and Oswego counties
Thursday evening will move a little farther northeast overnight into
the central portion of Oswego County, and eventually the northern
portion of the county. The band should still be pretty weak during
the evening, but may strengthen some overnight as the boundary layer
flow backs and improves fetch, and also as convergence forced by a
land breeze circulation strengthens. Lake induced equilibrium levels
will be around 10K feet, with a little deeper layer of dendritic
crystal growth available. This will allow for more favorable cloud
microphysics for Lake Ontario than Lake Erie. With this in mind,
this band of snow may produce 3-6 inches of accumulation across
Oswego County later Thursday night and early Friday morning. In this
case with an anticyclonically curved band on the northern edge of
high pressure, the band often does not extend very far inland, with
the heaviest snow amounts close to the lakeshore. Friday morning
boundary layer flow quickly becomes southwest, which will carry what
remains of the lake effect snow into northern Jefferson County. By
this time, any additional snow amounts will be light.

Things become more interesting again late Friday afternoon and
Friday night, as another clipper passes just north of Lake Ontario.
The clipper itself will bring some light snow to the region, with
accumulations less than an inch outside of lake enhanced areas. The
airmass remains plenty cold enough for lake effect snow as the
clipper passes by, and this will set the stage for significant lake
enhancement. Lake induced equilibrium levels will rise to about 15K
feet as the clipper passes by with improving moisture and cooling
temperatures aloft.

Off Lake Erie, expect a band of lake enhanced snow to intensify to
the north of Buffalo late Friday afternoon and early evening. This
band will then sweep rather quickly south across Buffalo Friday
evening, ending up in the western Southern Tier and weakening later
Friday night and early Saturday. The band may be quite strong as it
moves south across Buffalo, with high snowfall rates briefly. This
event may eventually need headlines, but the relatively fast band
motion may keep accumulations in the advisory range.

Off Lake Ontario, expect a band of lake enhanced snow over northern
Jefferson County Friday evening to move south into the Tug Hill
region overnight. Similar to Lake Erie, this band may become quite
strong as it moves south with an added boost of convergence from the
cold front associated with the clipper, and upslope flow into the
Tug Hill. Latest NAM/GFS guidance suggests the band may hold over
the Tug Hill a little longer, which may bring higher snowfall
totals. Eventually boundary layer flow will become northwest
Saturday morning, with weakening lake effect snow southeast of the
lake. This band should produce at least Advisory amounts, with at
least some chance of warning criteria snow on the Tug Hill Plateau
if the band does in fact hold there longer. Not enough confidence in
this scenario for a watch yet, but will continue to monitor.

On Saturday lake effect snow southeast of the lakes will quickly
diminish as high pressure builds into the region and the airmass
dries. This should end altogether by Saturday night as the ridge
builds across the lakes.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
With downstream blocking finally relaxing a bit, the persistent cold
air that we`ve been experiencing is expected to lessen a bit for the
start of next week. This will allow for temperatures to begin
moderating, with daytime highs returning to the mid to upper 30s.
Perhaps a few readings near 40 are possible Monday into Tuesday. The
pattern however remains fairly active; shortwaves will provide a few
chances for snow showers, and possibly some mixed precipitation. The
next cool down and chance for some lake effect snow showers comes
Wednesday into Thursday as ridging over the plains opens the door
for a northwesterly flow of arctic sourced air across the lower
Great Lakes.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Low pressure passing across Pennsylvania overnight will generate
light snow across all of western New York overnight. This will
result in generally MVFR cigs with IFR to LIFR vsbys in snow...while
VFR conditions will remain in place overnight for KART and KGTB.

As the low pressure moves away from the region on Thursday...most
areas will improve to VFR conditions. The exception will be
southeast of both lakes...including at KJHW where lake effect snow
showers will keep at least MVFR conditions in place.

Outlook...

Thursday night through Saturday...Mainly VFR except lake effect snow
showers will briefly impact terminal locations with IFR or lower
conditions possible.

Saturday night through Monday...Mainly VFR. A chance of snow showers
Monday.

&&

.MARINE...
A clipper low which will cause winds to increase overnight. This
will result in an extended period of conditions will generally fall
into the lower end of small craft advisory criteria. Winds and waves
may briefly drop off early Friday but winds will increase with
another system late Friday into Saturday with more small craft
headlines likely.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory until 7 AM EST Thursday for NYZ019>021.
MARINE...Small Craft Advisory until 10 AM EST Thursday for LEZ040-041.
         Small Craft Advisory until 7 AM EST Friday for
         LOZ043>045.
         Small Craft Advisory until 1 AM EST Friday for LOZ042.

&&

$$

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



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