Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 092158

Area Forecast Discussion
National Weather Service Buffalo NY
458 PM EST Sat Dec 9 2017

A weak area of low pressure will cross the region later tonight and
early Sunday with a few scattered light snow showers. Lake effect
snow will develop east of the lakes late tonight, and continue
through Sunday and Sunday night with locally heavy snowfall. High
pressure will bring a brief break on Monday. Low pressure will then
cross the Great Lakes and New England Monday night through
Wednesday, producing periods of widespread accumulating snow across
the region.


Tonight the east coast system will remain well east of our area, and
have no direct impact. The weak system to our west will drift across
the area and weaken even further, with a weak trough crossing the
eastern Great Lakes overnight. This weak trough will do nothing more
than bring an increase in cloud and produce a few scattered light
snow showers outside of lake effect areas, with little or no

Conditions will become favorable for lake enhancement by around
midnight however, as flow becomes better aligned with the trough
passage. Off Lake Erie, expect an area of lake enhanced snow to
briefly move into the Buffalo area around the midnight hour,
producing a quick inch or so of snow across northern Erie and
western Genesee counties. This area of lake enhancement will then
move south into southern Erie/western Wyoming counties and the
western Southern Tier later tonight. The lake enhancement combined
with upslope flow may produce a few inches of accumulation late
tonight and early Sunday morning across the higher terrain just
inland from the lake.

East of Lake Ontario, expect a similar scenario with some lake
enhanced snow developing at the east end of the lake late tonight.
This may briefly become fairly heavy shortly before daybreak across
the southern Tug Hill and Oswego County, where a few inches may
accumulate by sunrise Sunday.

Following this initial period of lake enhanced snow, we will
transition into a more pure lake effect event in the wake of the
weak clipper low. Lake induced equilibrium levels will hold between
10-12K feet later Sunday and Sunday night off both lakes. Background
synoptic scale moisture will be sufficient, with a deep layer of
dendritic crystal growth evident in soundings over both lakes. A weak
baroclinic wave and mid level trough will cross the region late
Sunday afternoon and Sunday night, possibly producing a few light
snow showers outside of lake effect areas. This system will also
provide deeper moisture and large scale ascent to aid lake effect

Off Lake Erie...

The lake effect snow may become disorganized for awhile Sunday
morning and midday as flow briefly becomes WNW and sheared. Expect
an area of relatively light snow to focus across the western
Southern Tier during this time, with only light additional
accumulations. By early to mid afternoon, boundary layer flow will
back to the WSW and become better aligned again. This should allow a
band of snow to intensify along the Lake Erie shore. This band may
initially focus on the Chautauqua and southern Erie County shorelines,
but should then move up into the more distant Buffalo Southtowns for
a few hours from mid afternoon through early evening, with a band of
heavy snow running from Angola to Hamburg and East Aurora, and
extending inland across Wyoming County. Snowfall rates may increase
to 1-2 inches per hour during this time frame.

This band of heavy lake effect snow will then drift slowly southward
across Southern Erie and Wyoming counties Sunday evening with
snowfall rates of 1-2 inches per hour, then move farther south back
into the western Southern Tier overnight. Flow will become northwest
with shear rapidly increasing by early Monday morning, with any
remaining lake effect quickly weakening across the western Southern

Expect total accumulations of 8-12 inches in the most persistent
bands across Southern Erie and western Wyoming counties, extending
into northern/western Chautauqua County and northwest Cattaraugus
County. Some local amounts of over a foot are possible in the Boston
Hills and possibly the southern portions of the more distant Buffalo
Southtowns. This is in a similar area to the previous event.

Off Lake Ontario...

Expect lake effect snow to be somewhat disorganized on Sunday with
multiple changes in wind direction. In the morning the band should
primarily be across Oswego County and the southern end of the Tug
Hill, possibly also clipping northern Cayuga/northeast Wayne
counties at times. This band will then move back north across the
Tug Hill into Jefferson County during the afternoon, and should
begin to gain some organization on the way. An approaching trough
Sunday evening will then lead to further intensification of the band
as convergence increases over the lake. Boundary layer flow will
become more westerly during this time, focusing the band across the
central Tug Hill Plateau through the middle of Sunday night.
Finally, flow will quickly become northwest and sheared by early
Monday morning, carrying rapidly weakening lake effect to the
southeast corner of the lake. The western end of the band may also
cross the Rochester area early Monday morning with minor

Expect the Lake Ontario band to reach peak intensity Sunday night
across the Tug Hill, when snowfall rates may exceed 2 inches per
hour. Total accumulations will range from 6-12 inches in the most
persistent bands across southern Jefferson, northern Oswego, and
Lewis Counties. The Tug Hill may see up to 15 inches or so total.


An arctic front will be pushing south and east into central NY
Monday morning trailed by a compact area of arctic high pressure. A
dry synoptic environment and subsidence brought on by the high
should work to dissipate lake effect snow showers south of the lakes
by midday. There should be at least a short break in the weather
during the afternoon before light snow begins to push into western
NY ahead of a slowly deepening surface low. A cool and dry airmass
will keep highs limited to the upper 20s to low 30s Monday.

The surface low will continue to deepen while it tracks from Lake
Superior to Lake Ontario Monday night into Tuesday morning.
Plentiful synoptic moisture and lift will be forced by the southward
digging longwave trough and near 500dm low. Additional support for
widespread snow will come from warm advection near 850mb. The low is
expected to exit across Lake Ontario into the Saint Lawrence River
Valley through Tuesday with winds in the wake of the low veering to
westerly and becoming gusty. Additional synoptic snow behind the
systems cold front is expected areawide through Tuesday in wrap
around moisture with lake effect snows developing east of the lakes
as 850mb temps cool aloft. A blend of model QPF with SLR increasing
from 15:1 to 20:1 in the cooling airmass will bring a general 2-3
inches Monday night and another 2-4 inches Tuesday. The developing
lake snows could bring more than 4 inches in the snow belts
especially with BUFKIT profiles indicating lake induced equilibrium
levels may push above 10kft. While the synoptic snow at this time
looks to run sub to near advisory level, this will be the beginning
of another extended lake snow event east of the lakes with headlines
possible. Temperatures Monday night will dip into the teens and low
20s with highs int the mid 20s to around 30 Tuesday. Gusty winds in
the wake of the systems cold front should run 25-35 mph driving wind
chills in the teens.

Tuesday night through Wednesday lake snows are expected to continue
but to the southeast of the lakes as the steering flow veers again
to northwest in the wake of the core of the 500mb low pivoting
across northern NY. BUFKIT cross sections indicate healthy lake
plumes with equilibrium heights running 10-15kft and sufficient
synoptic moisture and lift intersecting the dendritic snow growth
zone. This will perhaps be the most significant time period of
accumulating lake snows where headlines continue to look very
possible. With this best period being still 4 days out will continue
with the mention in the Hazardous Weather Outlook. As the core of
the 500mb low passes over our region we will experience the coldest
air yet this month with lows dipping into the single digits to teens
Tuesday night and only peaking in the teens to maybe 20 on
Wednesday. Lake effect appears to begin to weaken Wednesday night
as high pressure over the Ohio Valley may build across western NY.


A fair amount of uncertainty remains regarding Thursday/Friday, as
the forecast revolves around the timing of another clipper low
progged to drop across the Great Lakes. Southerly flow ahead of this
system should bring an end to lingering lake effect Thursday, with
the aforementioned low bringing more snow showers in the Thursday
night to Friday night timeframe, depending on the model.
Temperatures will remain below average through the end of the week,
as the region will remain embedded within the longwave trough.

As we move into the end of the week, the longwave trough pattern
that has dominated the eastern half of the country of late shows
signs of breaking down as we move into the weekend, with a lower
amplitude flow regime allowing milder Pacific air to wash across the
northern tier of the country and potentially bringing temperatures
back above freezing and closer to climatological normals in the
mid/upper 30s next weekend. However, longer range guidance suggests
that this break may only be temporary, as the longwave trough
becomes re-established over the East in the week following.


A weak system will cross the area tonight and produce a few
scattered light snow showers. More importantly, it will begin to
bring more favorable conditions for lake effect snow again overnight
and into Sunday. Lake enhanced snow will develop east of Lakes Erie
and Ontario later tonight. This may impact KBUF and KART for a few
hours initially, then will move south of those two airfields late
tonight into Sunday morning as the flow becomes more westerly. This
will direct most of the lake effect snow into the western Southern
Tier off Lake Erie, and the Tug Hill/Oswego County off Lake Ontario.
The lake effect will produce local areas of IFR later tonight
through Sunday morning.

Lake effect snow may be somewhat disorganized for awhile Sunday
morning, but should intensify again later Sunday afternoon as
conditions become more favorable. Off Lake Erie, this intensifying
snowband along the Lake Erie shore south of Buffalo will move north
to a point just south of KBUF by mid afternoon, before drifting a
little south again by Sunday evening. Off Lake Ontario, the
intensifying snowband over the Tug Hill will move north to near KART
later in the afternoon and evening, before moving back south to the
Tug Hill during the late evening Sunday. Both of these bands will
produce local Very low IFR conditions.

Sunday night...Heavy lake effect snow east of the lakes with
local LIFR, otherwise scattered snow showers with local MVFR.
Monday...Lake effect snow showers with local IFR southeast of the
lakes early, then improving to VFR.
Monday night through Wednesday...Areas of IFR with periods of
Thursday...Spotty MVFR/IFR with scattered snow showers.


A coastal low will remain well off the east coast, but will combine
with a weak low moving across Quebec to tighten the pressure
gradient across the eastern Great Lakes. This will bring Small Craft
Advisory conditions to both lakes Erie and Ontario from early Sunday
morning through late Sunday night. High pressure will then bring a
return to lighter winds on Monday.


NY...Lake Effect Snow Warning from 4 AM Sunday to 7 AM EST Monday
     for NYZ006>008.
     Lake Effect Snow Warning from 1 AM Sunday to 7 AM EST Monday
     for NYZ012-019-020-085.
MARINE...Small Craft Advisory from 4 AM Sunday to 4 AM EST Monday for
         Small Craft Advisory from 4 AM Sunday to 4 AM EST
         Monday for LOZ042>045.



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