Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 160547

Area Forecast Discussion
National Weather Service Buffalo NY
1247 AM EST Tue Jan 16 2018

Weak low pressure will cross our region overnight and Tuesday
while bringing a period of light snow to most areas. Following
the passage of this system...a continued flow of cold air will
produce some limited lake snows downwind of the lakes through
midweek...before a pronounced day to day warming trend arrives
late in the week and then continues through next weekend.


Occasional light snow will continue overnight. Less than an
inch of additional accumulation is expected. Temperatures will
remain steady in the upper teens/low 20s overnight.

A weak clipper system centered over southern Lower Michigan
will slide eastward across our area through this period...while
continuing to slowly but steadily weaken.

Weak warm air advection/isentropic upglide out ahead of this
system will continue to spread occasional light snow across the
region from west to east through the early overnight hours...with
the steadier synoptic snows then winding down in a similar manner
through the rest of the night and Tuesday as the best forcing/
deeper moisture slide off to our east.

In terms of snowfall accumulations...the generally weak forcing
attendant to this system and the consequently light nature of
the snow will help to keep overall accumulations on the light
to modest side...with most areas picking up only an inch or two
of fresh snowfall. This said...somewhat higher amounts of 2-4
inches will be possible along the south/southeast-facing slopes
of the higher terrain in the Southern Tier/Finger Lakes and
across southern portions of the Tug Hill Plateau...where some
orographic enhancement will come into play.

Following the passage of this system...a southwesterly to westerly
flow of somewhat colder air will gradually infiltrate our region
during the course of Tuesday...with 850 mb temperatures dropping
to between -12C and -15C. While this is sufficiently cold enough
to provoke a lake response...a rather low cap of only 3-5 kft and
the presence of at least some directional wind shear should help
to keep any such response confined to some scattered flurries or
very light snow showers.

Regarding temperatures...these will hold steady or slowly rise
in most locations tonight owing to the increasing cloud cover/
weak warm air advection regime out ahead of the clipper...with
only the North Country (where clouds will be thinner/higher
initially) seeing some semblance of a temperature drop this
evening. Expect nighttime mins to range from the upper teens to
lower 20s south of Lake the 10 to 15 range across
the North Country. Following this...highs on Tuesday will then
range in the mid to upper 20s in most places.


Tuesday evening the last of the synoptic snow will be exiting the
eastern portion of the area as a weak baroclinic leaf develops over
eastern PA and eastern NY, marking a weak wave along the frontal
boundary. Otherwise our attention turns back to the mesoscale, as a
relatively muted lake response begins. Lake induced equilibrium
levels will start Tuesday evening only around 5K feet, but then
improve to around 7K feet late Tuesday night and Wednesday morning.

Off Lake Erie...

Obviously ice cover will be a major limiting factor with the
majority of the lake ice covered. Recent satellite images do show a
substantial area of open water between Dunkirk and Long Point, and
the ice west of that is not fast ice, with numerous leads and thin
spots apparent in MODIS imagery from yesterday. With this in mind,
there is still enough open water to provide some limited lake
response, and frictional convergence is always present with or
without ice.

Expect the most concentrated area of snow showers to be found from
Southern Erie and western Wyoming counties into the western Southern
Tier Tuesday night and Wednesday, with peak organization coming late
Tuesday night and early Wednesday morning. There may also be a few
snow showers reaching the Buffalo Metro area at times, as a weak
band will often form from just east of Long Point and hugs the
northern shore into Buffalo when ice is present on the lake, which
alters where convergence sets up. Accumulations will be limited to 1-
2 inches Tuesday night, and another inch or so Wednesday. A few
flurries or light snow showers may linger into Wednesday night near
Buffalo, with little or no additional accumulation.

Off Lake Ontario...

Weak flow will initially keep much of the lake effect snow over the
lake Tuesday evening, although the eastern end may move onshore in
Oswego County. Later Tuesday night WSW flow becomes better
established across the lake, with lake effect snow showers
increasing across southern Jefferson County and the Tug Hill. This
band will settle south across Oswego County early Wednesday morning
as boundary layer flow veers briefly to west, and then heads back
north across the Tug Hill to Jefferson County again on Wednesday as
flow backs to the southwest.

The movement of the band and shallow inversion heights will keep
accumulations in check, with 1 to 3 inches Tuesday night and another
2 to 3 inches Wednesday in persistent bands. This should keep
amounts a little under advisory criteria. What remains of the lake
effect will diminish to scattered snow showers Wednesday night and
Thursday, although may not end completely with marginal lake induced
instability remaining. Any additional accumulations should be

Outside of lake effect areas, Wednesday and Thursday will be mainly
dry for the rest of the region with variable amounts of clouds.
Expect highs Wednesday to be in the low to mid 20s in most areas,
with upper teens across the higher terrain. By Thursday highs will
recover into the mid to upper 20s.

Thursday night and Friday morning a fast moving and rather sharp mid
level trough will pass over or just north of Lake Ontario. This
system will bring an increase in clouds to much of the region, and
also provide a little better environment for lake effect snow again
east of Lake Ontario. This may produce some additional minor
accumulations centered on the Tug Hill region. This system will move
out quickly on Friday with any snow ending east of Lake Ontario.
Temperatures will continue their slow rise, with highs in the mid
30s by Friday afternoon.


Another mid-winter thaw will be in the works as we move into the
weekend. A surface low is currently forecast to pass by to our north
as it tracks from northern Ontario Friday night to Labrador by
SUnday. Relatively warm and moist GOMEX-sourced air will be drawn
across our region and into this low, with a warm front crossing the
forecast area Friday into Friday night. While a few light snow
showers may be possible as the front crosses the area, the bulk of
the vertical forcing will remain well to our north across Canada,
and as a result pops should remain low into Saturday. Temperatures
should gradually rise through the 20s Friday night, with readings
cracking 40 degrees across many locales by Saturday afternoon.

Temperatures will continue to rise and moisture will gradually
increase across the area as we move into the second half of the
weekend as southerly flow and GOMEX moisture return strengthens in
response to lee-side cyclone development across the central Plains.
Temperatures will climb well into the 40s, and some areas may flirt
with 50 Sunday afternoon, as warm air surges north across the region
in advance of the deepening cyclone moving into the Midwest. The
warming temperatures will be accompanied by increasing clouds
however, as this moisture deepens across the region. Models
currently indicate that we should see a more substantial chance
for rain moving into far western New York by late Sunday night,
as the low-level jet associated with the low approaches the
area. Rainy and blustery conditions can be expected on Monday,
as the aforementioned low cuts across the central Great Lakes.


A weak clipper system centered over southern Lower Michigan will
slide eastward across our area through the TAF period...while
continuing to slowly but steadily weaken. This system will continue
to spread occasional light snow across the region from west to east
through the early overnight hours...with the steadier synoptic snows
then winding down in a similar manner through the rest of the night
and Tuesday.

Largely VFR flight conditions out ahead of the snow will
deteriorate to largely IFR visibilities and MVFR ceilings as
the snow overspreads our region...with gradual improvement
to MVFR/VFR then expected overnight and Tuesday as the steadier
snows diminish from west to east.

Tuesday night through Friday...localized MVFR to IFR possible in
scattered to occasionally more numerous lake effect snow showers
east of the lakes...with mainly VFR conditions elsewhere.
Saturday...Mainly VFR with a chance of light rain.


A weakening area of low pressure will cross our region overnight
and Tuesday. This will result in modest southeasterlies veering
to southerly overnight...then to westerly while also picking up a
little on Tuesday. This said...conditions will still remain below
advisory levels through Tuesday.

On Wednesday high pressure will ridge across the Ohio Valley...
while low pressure meanders its way across James Bay. Lingering
cold air and the tightening pressure gradient in between these
two systems will bring increasing winds and waves to those portions
of Lakes Erie and Ontario that are still ice free...and as such will
likely necessitate another round of Small Craft Advisories.





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