Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 241954
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
254 PM EST Tue Jan 24 2017

.SYNOPSIS...
A strong low pressure system will shift into the Gulf of Maine
tonight then move south of Nova Scotia Wednesday. Light snow will
taper off this evening as high pressure crosses the region tonight
and Wednesday. Another low pressure will then cross the region
Thursday ushering in a pattern change back to mid-winter conditions.
Heavy lake effect snows are possible east of lower Great Lakes
through the weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
A coastal storm is centered just south of Long Island this
afternoon. This system continues to circulate Atlantic moisture
westward across New York state. This moisture is interacting with a
deformation/frontogenesis region that is showing up on radar from
about Watertown southwest across much of western NY. Another 1 to 2
inches will likely fall in this deformation band through the
afternoon hours. Winter Weather Advisories linger for the Genesee
Valley northeastward to Watertown due to some slippery travel
likely on untreated surfaces where the deformation band lingers.

Tonight the coastal low will lift to the Gulf of Maine. The
deformation axis and synoptic moisture will pivot northeast with
the low which will bring an end to the widespread snowfall. While
the deep moisture will be stripped away tonight, model moisture
profiles show low level moisture will linger. This will keep mostly
cloudy skies overnight with some upslope northwesterly flow possible
keeping some lingering flurries or possibly even some freezing
drizzle in the higher terrain of the interior Southern Tier and
western Finger Lakes. Freezing Drizzle is possible due to the lack
of moisture in the snow growth zone. Confidence is low however so
kept POPs at slight chance. Temps tonight are only expected to slip
back into the mid to upper 20s.

A ridge of high pressure will shift across the forecast area on
Wednesday with most of the day seeing dry weather with mostly cloudy
skies. Another area of low pressure will be approaching from the
Central Great Lakes late in the day with precip likely holding off
until Wednesday evening. Temperatures will warm above normal as the
flow becomes southerly ahead of the next system. High temps will
range from the low to mid 40s across Western NY to the mid to upper
30s for Central New York.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
Wednesday night and Thursday a potent closed mid level low will move
east through the Central Great Lakes and open up with time as it
gets absorbed by another trough moving through Quebec. At the
surface, low pressure will pass just north of Lake Erie and Lake
Ontario late Wednesday night and Thursday, with a trailing cold
front moving southeast across the area Thursday afternoon and
evening. Precipitation will come in several batches with this
system. A weak baroclinic wave will develop ahead of the trough
Wednesday night which is likely to produce rain showers crossing the
area from west to east.

The associated 500mb trough will cross the area on Thursday, with
associated DPVA resulting in another round of precipitation generally
light precipitation. This will be followed by more significant (but
localized) amounts Thursday afternoon and evening as winds shift to
the west behind the cold front and generate an upslope flow east of
the Lakes.

Precipitation type will be elevation dependent from Thursday morning
through early to mid afternoon, with mainly rain at lower elevations
and a rain/snow mix changing to all snow across higher terrain.
Temperatures will cool aloft with the passage of the disturbance
which will change precipitation to all snow late in the day. This has
the potential to produce several inches of snow across the Western
Southern Tier extending in to the Boston hills.  A bit more snow is
likely on the Tug hill, possibly approaching advisory amounts. After
this, slightly drier air should briefly build behind the front which
will diminish snowfall rates late Thursday night. Accumulation
across lower terrain should be minimal, mainly less than an inch.

By Friday, temperatures aloft will be cold enough to support lake
effect snow with 850mb temps around -10C through Friday night. The
key to our forecast will be the progression of a shortwave which
model consensus brings across the area late Friday. Westerly winds
will briefly shift to the southwest in advance of this shortwave,
then return to the west behind it. The shortwave will also enhance
moisture which will result in a period of moderate to heavy snow
east of the lakes. There is still uncertainly in the timing and
location of lake effect bands because of subtle differences in the
progression of the shortwave and differences in forecast wind
fields. In general, the greatest amounts should be focused across
the traditional snow belts east of the lakes, however the band may
meander north toward the Buffalo metro area late Friday in advance
of the shortwave. There is not yet enough forecast confidence to
issue a watch, however it is possible snowfall amounts may
approach warning criteria in some locations on Friday and Friday
night. Either way, this appears to be the start of a much more
winter-like pattern than it has been for the past couple weeks.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Typical mid winter weather will become established again through the
long term period after a several week hiatus. A fundamental pattern
change will take place across North America, with a ridge building
over the west and a longwave trough becoming established over the
eastern half of the continent late in the week through next weekend.

Our area will be in the active region near the base of the longwave
trough, with numerous weak shortwaves moving through the base of the
trough. Each of these shortwaves may produce a few light snow
showers across much of the region, and will also bring subtle
variations to the low level flow, moisture depth, and cold air
structure which will impact ongoing lake effect snow.

By Saturday and Sunday model guidance begins to show some spread,
with several shortwaves moving through the longwave trough and
possibly backing winds more WSW at times.

The airmass is not overly cold by late January standards, with 850mb
temps dropping to around -12C over the weekend. Temperatures are
fairly cold at 700mb however, and this combined with deep moisture
will allow lake induced equilibrium levels to rise to near 10K feet.
The favorable instability and longevity of the setup suggest
significant accumulations are possible east of the lakes. A
comparison of the surface and upper level patterns to our locally
developed lake effect analogs show a good match to significant
events for the Chautauqua Ridge and Tug Hill/Oswego County. CIPS
analogs also support the idea of a significant event. 3-4 day storm
totals may very well reach several feet east of both Lake Erie and
Lake Ontario from late week into the weekend.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
Widespread IFR conditions continue this afternoon as a coastal storm
system moves just east of southern New England. All sites will see
visibility and ceiling restrictions in light snow through the
afternoon. Snow will taper off and end from south to north this
evening. Cigs will lift to MVFR tonight except at KJHW which will
hold at IFR with low stratus. High pressure will shift across the
region on Wednesday with KBUF/KIAG/KROC improving to VFR.

Outlook...
Wednesday night and Thursday...VFR/MVFR with a chance
of rain and snow.
Friday to Sunday...VFR/MVFR with IFR in lake effect snow showers.

&&

.MARINE...
A coastal storm system will churn northward off New England tonight.
Northerly winds 15 to 25 knots over central Lake Ontario this
afternoon will subside by tonight.

Ridging will build in briefly tonight and Wednesday, which will
provide light winds and wave action. We will return to more typical
mid-winter conditions by this weekend with lake effect snows and
likely much choppier conditions on both lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Winter Weather Advisory until 7 PM EST this evening for
     NYZ003>007-011>014-020-021.
MARINE...Small Craft Advisory until 7 PM EST this evening for LOZ043-
         044.

&&

$$

SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...APFFEL
LONG TERM...HITCHCOCK
AVIATION...SMITH
MARINE...SMITH


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