Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 082204
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
504 PM EST Fri Dec 8 2017

.SYNOPSIS...
Fair and largely dry weather will then follow for tonight and
Saturday, before a passing weak low pressure system brings a general
light snowfall Saturday night and Sunday, along with some areas of
lake enhancement east of the lakes. Otherwise, temperatures will
remain at seasonable levels through the weekend.

&&

.NEAR TERM /THROUGH SATURDAY/...
Tonight, an elongated ridge of high pressure will gradually build
into the area from the mid-Atlantic states. This will result in a
quiet and largely dry night, though we still cannot rule out a few
more flurries northeast of the lakes in conjunction with a possible
brief increase in low level moisture/subtle veering of the low level
wind field. If the latter do manage to form, these should shut down
altogether by very late tonight as we dry out again and the steering
flow turns more southerly. Otherwise, overnight lows will range from
the mid to upper teens across interior portions of the Southern
Tier/ Finger Lakes/North Country to the lower 20s elsewhere.

On Saturday, our region will be caught in the squeeze play between
one area of low pressure tracking just offshore of the mid Atlantic
and New England coastlines, and a second weak low pushing eastward
across the Upper Great Lakes. The swath of compensating subsidence
and relatively drier air in between these two systems will result in
a dry and quiet day across our region, along with at least some
partial sunshine. With some moderation in our airmass, we can expect
daytime highs to recover to the mid to upper 30s in most locations,
with a few of our normal warm spots in the Genesee Valley and Finger
Lakes potentially reaching the 40 degree mark.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
Several shots of arctic air will ensure it will remain cold with
more snow on the way for the second half of this coming weekend into
the start of next week. Multiple winter weather headlines may become
possible as confidence increases for both synoptic and lake effect
snowfall.

A lingering deep eastern CONUS upper level longwave trough will keep
arctic sourced air across the Great Lakes region. A continually
deepening coastal storm should remain well to our east and tracking
into the Canadian Maritimes by Sunday morning. For our region, the
first round of synoptic snow will come from a trailing mid level
shortwave trough and weak surface low crossing the eastern Great
Lakes Saturday night. The trough will support enough snow showers
for a general coating to an inch or so of accumulation areawide
overnight. In the wake of the trough, cold advection will push 850mb
temps down to around -14C supporting developing lake effect snows
east-southeast of both lakes. This will support higher snowfall
totals in the traditional snowbelts of the western Southern Tier and
southeast of Lake Ontario. Temps will dip into the teens to low 20s.

Sunday, steering level winds will back to west or west-southwesterly
with accumulating lake snows lifting north along the east of both
lakes. Lake induced equilibrium levels of over 10kft along with
sufficient synoptic scale moisture will support well organized single
bands of lake snow. Several additional inches of snow could
accumulate east of the lakes. Wind may even back enough ahead of
another approaching shortwave trough to allow for the northern edges
of the lake bands to reach the Buffalo and Watertown metro areas.
Warning threshold snowfall totals could certainly be possible
although the transient nature of the lake bands, amount of wind
shear and issues with more exact placement at this range will
preclude a Winter Storm Watch headline at this time. Confidence
is high enough however to insert a mention of the lake snows in
the Hazardous Weather Outlook for Saturday night through Sunday.
In addition to the lake snows, winds will become gusty as cold
advection supports mixing down of a 30-40kt low level jet. It
will also be colder across the region with temperatures
struggling to reach the mid 20s to around 30. Wind chills will
make it feel like only in the teens.


Another upper-level trough and surface arctic front is forecast push
south across western and central NY Sunday night. This front will
bring another opportunity for a widespread fresh coating to an inch
of snow accumulation while areas south and east of both lakes will
likely see additional enhanced lake snows and accumulations. Drier
incoming arctic sourced air behind this front may actually work to
weaken or dissipate the lake snows by Monday morning. Temps will
again dip into the teens and low 20s overnight.

Monday should be another cold day in the wake of the arctic front
but the previously mentioned drier airmass has caused POPs Monday
morning to be held in the medium chance range. Otherwise we will be
looking at a clipper system dropping across the upper Midwest. The
operational GFS and ECMWF models are in better agreement with the
12z runs. Warm advection and overrunning ahead of this approaching
storm system will likely spread some light snow over our region by
late in the day on Monday where likely POPs remain for the western
Southern Tier. Monday night, the models are a near lock step
shifting the center of the clipper into western NY. This had lead to
a continuation of broadbrush likely POPs for widespread light snow
shifting across our region through Monday night. High temps within
a few degrees of freezing Monday are expected to drop into the teens
to near 20 degrees Monday night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
The longwave trough will remain firmly entrenched across the eastern
U.S. through next week, resulting in cold temperatures and continued
unsettled and snowy weather through next week. The main concern for
the coming week centers around a clipper low that is currently
expected to drop across the Upper Midwest Monday before tracking
across the lower Great Lakes Monday night into Tuesday. This low is
also expected to deepen significantly as it moves across the lower
Great Lakes as it encounters increasingly favorable upper level
dynamics.

While the track of the low is a little farther north than previous
runs, the bulk of western and north-central New York is expected to
remain within an area of deep isentropic uplift in advance of the
low. This will likely result in a widespread snowfall Monday night
into Tuesday that may end up bringing at least advisory level
snowfall amounts to a broad swath of the forecast area. Of greater
concern is the potential for heavy snow on Tuesday as the low passes
to our east. The combination of deep baroclinicity on the western
edge of the low and strong northerly flow adding in lake enhancement
off Lake Ontario has the potential to deliver significant snowfall
to portions of western and central New York, with the Rochester area
being an area of particular concern.

The low will rapidly track off to the northeast Tuesday evening,
leaving a sub-arctic airmass in its wake. With temperatures plunging
into the teens to single digits, with potentially sub-zero wind
chills on brisk northwesterly flow, lake effect snows are likely to
impact areas south of Lake Ontario, as well as the Chautauqua Ridge -
 particularly if a Lake Huron connection can develop.

Lake effect snows are currently expected to persist through
Wednesday night before flow backs to the south/southwest ahead
of another synoptic system that may impact the region late in
the week. After a cold day on Wednesday, featuring highs in the
teens, readings should climb back into the 20s, and possibly
warmer, on Thursday. There is considerably more uncertainty on
the track of the late-week system, with the GFS suggesting a
broad low tracking across the lower Great Lakes, bringing a
widespread synoptic snow Thursday/Thursday night, while the
ECMWF/CMC favoring a more northerly track that suggest more of a
lake effect scenario for Thu/Thu Night.

&&

.AVIATION /22Z FRIDAY THROUGH WEDNESDAY/...
Tonight and Saturday, an elongated ridge of high pressure will
largely lead to continued fair dry weather and VFR conditions.
The one possible exception to this will be found northeast of
the lakes tonight, where lingering lake effect cloud cover
could potentially dip back to MVFR levels for a time.

Outlook...
Saturday night...Deterioration to MVFR/IFR with snow developing.
Sunday through Monday...Areas of IFR in lake effect/lake enhanced
snow east and southeast of the lakes...otherwise MVFR/VFR.
Monday night and Tuesday...IFR in snow.
Wednesday...Areas of IFR in lake effect snow southeast of lakes...
otherwise MVFR/VFR.

&&

.MARINE...
Low pressure over western Quebec will make its way to Labrador
through Saturday, while weak high pressure builds across New York
State. Consequently, a brisk southwesterly flow across our region
this evening will gradually weaken overnight and Saturday morning,
allowing for widespread advisory-worthy winds and waves to diminish
to below advisory levels.

This improvement in conditions will be fairly short-lived however,
as winds will freshen out of the northwest and waves will build again
following the passage of another weak surface low/cold front Saturday
night and Sunday morning. After that, a continued brisk westerly to
southwesterly flow is expected for the rest of Sunday and Sunday
night.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory until 10 AM EST Saturday for LEZ040-041.
         Small Craft Advisory until 10 PM EST this evening for
         LEZ020.
         Small Craft Advisory until 7 AM EST Saturday for
         LOZ043-044.
         Small Craft Advisory until 4 AM EST Saturday for LOZ042.
         Small Craft Advisory until 10 AM EST Saturday for LOZ045.
         Small Craft Advisory until 1 AM EST Saturday for
         SLZ022.

&&

$$

SYNOPSIS...CHURCH/JJR
NEAR TERM...CHURCH/JJR
SHORT TERM...SMITH
LONG TERM...WOOD
AVIATION...CHURCH/JJR
MARINE...CHURCH/JJR



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