Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 152141
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
441 PM EST Mon Jan 15 2018

.SYNOPSIS...
An area of low pressure will cross the region tonight and tomorrow,
spreading light snow across the Eastern Great Lakes. Temperatures
will remain just below normal mid-week, with some limited lake
effect snow to the southeast and east of the Great Lakes.
Temperatures will begin to moderate to start next weekend, warming
above normal by the end of next weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
This afternoon an area of low pressure is nearing the Central Great
Lakes, while arctic high pressure departs over southern Quebec. A
southerly wind and warm air advection aloft has allowed for surface
temperatures to moderate from the weekend cold with many places now
into the lower 20s.

For this late afternoon and evening light snow will spread across
WNY. Isentropic upglide will be weak, and convergence will diminish
around a weakening surface low...though with a nearing upper level
shortwave there will be ample lift for light snow to develop. As
such, and with an arctic source region to this system`s moisture,
snowfall rates will be minimal...generally on the order of just a
few tenths of an inch per hour.

Light snow is expected to spread east of Lake Ontario after
midnight. The southerly winds may bring some downsloping effects,
limiting overall snow across the Lake Plain and Genesee Valley,
while some of the hills of SW NYS and the southern Tug Hill may have
orographic upslope enhancement.

Overall snow tonight and tomorrow will range from 1 to 4 inches.
Greatest totals will be SW NYS, and the southern Tug Hill...while
areas closer to the southern Lake Ontario shoreline and the Genesee
Valley will struggle to accumulate more than an inch. Within the
cold airmass snow is expected to be dry...and flake size may remain
small.

Tomorrow morning drying in the mid levels will end snow from west to
east. As the weakening surface low hangs up over Central New York,
light synoptic snow may linger well into the afternoon hours east of
Lake Ontario. Aloft temperatures at 850 hpa will lower to around -12
to -14C. Some limited lake effect snow may develop on a southwest to
westerly flow late tomorrow...though weak instability and still a
fair amount of wind shear should not result in any significant
bands.

Temperatures will not lower much tonight, and may increase a tick or
two as clouds thicken tonight. Lows will range through the teens to
lower 20s. Coldest spots will be interior locations east of Lake
Ontario where cirrus may remain thin enough this evening to allow
for overnight lows in the upper single digits. Highs on Tuesday will
be in the mid to upper 20s.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH FRIDAY/...
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
minimal.

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.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
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.

&&

.AVIATION /22Z MONDAY THROUGH SATURDAY/...
An area of low pressure nearing the Central Great Lakes region this
afternoon will spread a period of light snow across the TAF
sites...mainly between 23Z tonight and 12Z tomorrow. Snow may linger
through about 15Z east of Lake Ontario...including the KART
airfield.

Visibilities will diminish to IFR within the snow, with ceilings
lowering to MVFR. Winds will remain generally light within the snow,
with southeast flow this afternoon veering to southwesterly by TAF
closure behind the storm system.

Outlook...
Monday night...Light snow with areas of IFR.
Tuesday through Friday...A chance of snow showers with spotty MVFR
to IFR, especially east of the lakes with local lake effect snow.
Saturday...Mainly VFR.

&&

.MARINE...
Southeast winds today will veer to southwest and eventually westerly
tomorrow as a weakening area of low pressure cross the Eastern Great
Lakes region.

Cooler air will build across the lakes mid-week...such that CAA and
westerly flow will bring waves over 4 feet Wednesday...with small
craft advisories becoming likely.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...THOMAS
SHORT TERM...HITCHCOCK
LONG TERM...WOOD
AVIATION...THOMAS
MARINE...THOMAS



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