Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 252328

Area Forecast Discussion
National Weather Service Buffalo NY
728 PM EDT Tue Oct 25 2016

A cold northwesterly flow will continue tonight and into tomorrow
morning with isolated lake effect precipitation southeast of the
lakes. A low pressure system tracking out of the Midwest is then
expected to cross the lower Great Lakes tomorrow night and Thursday,
bringing widespread rainfall, and hilltop snowfall. Another round of
rainfall will be possible later this weekend, as another low
pressure system drops across the region.


Water Vapor imagery this afternoon displays a large upper level low
over New Brunswick and the Gulf of St. Lawrence. Deep northwesterly
flow is found behind this feature, across the Eastern Great Lakes
region and ahead of a ridge across the Central Plains. A shortwave
is cresting this ridge this afternoon.

At the surface high pressure is found just south of James Bay, while
a surface low continues to weaken over the Gulf of St. Lawrence.

For tonight northwest wind will continue across the region, this
between the surface high to our northwest and surface low across
Eastern Canada. As the surface high drops southward towards our
region, and the surface low weakens northwest winds will diminish
through the evening hours.

It will remain chilly through the overnight period, even though
there will be slight warm air advection through the night. Clearing
skies outside of lake effect clouds will allow for overnight lows to
drop down to near freezing, and even below. There will not be any
mention of frost, nor headlines as that program has ended for the

Lake effect clouds will continue through the night, with isolated to
at best scattered lake activity. Drier air associated with the
nearing surface high, along with falling lake induced equilibrium
heights due to warm air advection will limit the lake response
through the night. Any precipitation south and southeast of mainly
Lake Ontario could contain graupel or light snow flurry.

Tomorrow will remain mostly dry under a mix of clouds and sunshine.
With a pool of cold air remaining overhead daytime highs will be
limited to the low to mid 40s. The upstream shortwave cresting the
upper level ridge will reach the Central Great Lakes region tomorrow
afternoon. This will spread clouds across Western New York later in
the afternoon, though any rainfall will likely wait until the early
evening hours to fall.


Upper level energy will be working through the Midwest into the
Great lakes Wednesday night, as a weak surface low rides across the
southern Great Lakes. Plenty of moisture advection within a 45 to 50
knot low level jet focused on the Ohio valley and lower Great Lakes
to support developing rain Wednesday night. Potential precipitation
type issues develop, especially for areas east of the Genesee
Valley. Temperatures should slowly fall off of their afternoon highs
as cloud cover increases with the northeast progression of the warm
front. Most of Western New York will remain warm enough for the
precipitation arriving during the evening to remain as all rain.
However, higher elevations of the Southern Tier and Finger Lakes
will likely see snow mixing in with the rain, as temperatures fall
toward freezing. Farther to the east, as the precipitation reaches
there later at night into Thursday morning, we could see at least a
few of hours of snowfall, with accumulations of around an inch, with
perhaps the the highest portions of the Tug Hill, seeing a 2 to 4
inch accumulation in some locations, as temperatures there will
experience the longest period of time near or just below freezing.

The southeasterly flow ahead of the low will be well placed to
generate reasonably strong downsloping winds off the Chautauqua
Ridge along the Lake Erie shoreline Wednesday night into early
Thursday morning, perhaps gusting as high as 45 mph.

Precipitation will change over to rain everywhere on Thursday as the
compact area of low pressure system tracks directly across the lower
Great Lakes, with strong warm air advection and diurnal component
coming into play. The strong warm air advection pattern will
generate a widespread swath of isentropically driven rain, with many
locations seeing upwards of an inch of rainfall.

This rain will give way to rain showers Thursday night, as the low
shifts east of Lake Ontario and a secondary low develops along the
Mid-Atlantic coast. Developing cold air advection on the backside of
the system on a fairly uniform west-northwest flow will likely
support lake effect rain showers downwind of the lakes, with perhaps
a few snowflakes mixing in across the hills of the Southern Tier and
Tug Hill towards Friday morning, when temperatures fall into the mid
30s. Lows in the upper 30s elsewhere should preclude any snowfall

Lake effect showers should taper off on Friday as surface ridging
and warm advection take hold across the region. This ridging will be
embedded within a highly progressive, low-amplitude, flow aloft. In
fact, there will little in the way of clearing associated with the
ridge as it rapidly crosses the area and the next warm front sets up
across the lower Great Lakes Friday night into Saturday.

Models differ with regards to the exact track and speed of the low
pressure system that will be aiding in the development of the warm
front across the area, but all guidance currently indicates that
Saturday should be another wet day across Western and North-Central
New York.


GFS and ECMWF are close in agreement as to the timing and track of
the surface low on Sunday. GFS is a bit faster but both models move
the low eastward across the Lake Ontario basin and northern NY. Rain
should diminish following cold front passage, likely during the
afternoon given a compromise between models, then colder air on
northwest wind brings some lake effect response Sunday night. 850mb
temps fall to around -2C overnight, then this bubble of colder air
will be quickly offset by burgeoning warm advection on Monday.
Ridging aloft should suppress any precip for Monday and Tuesday.
850mb temps will climb to +10C by midday on Tuesday.

High temperatures on Sunday will reach the mid to upper 50s across
Western and Central NY with lower 50s for the North Country, then
temperatures will fall Sunday night following the cold front with
lows in the upper 30s to lower 40s. There should be a quick rebound
on Monday with highs once again in the lower to mid 50s, then lower
40s Monday night. The warmer air moving in on Tuesday will boost
temperatures to the upper 50s and low 60s over northern NY and the
lower to mid 60s for Central and Western NY.


For the 21Z TAF cycle, lake effect clouds southeast of Lake
Ontario should remain at around 4-5k ft and in the VFR flight
category. High pressure centered just to the north of Lake Ontario
will nose southward across the TAF sites tonight, providing a
partial clearing, while maintaining VFR flight conditions with
light winds.

Northwest winds will begin to back to northerly tomorrow noontime,
with continued VFR flight conditions through Wednesday evening.

Wednesday night and Thursday...MVFR/IFR with rain showers likely.
Friday...MVFR with a chance of lake effect showers.
Saturday and Sunday...MVFR/IFR with rain becoming likely.


Northwest winds will continue to rush over the Eastern Great Lakes
region this afternoon with winds generally 15 to 20 knots across
Lake Ontario until about sunset. This supports low end small craft
waves of 3 to 5 feet which should subside between 6pm and 8pm.
High pressure over Canada will nose southward over Lake Ontario
tonight and diminish the winds, and likewise the wave heights.

Winds and waves will remain light tonight and tomorrow. Later
tomorrow night and into Thursday an easterly flow will begin to
build wave heights on the western portion of the Eastern Great Lakes
bodies of water.


MARINE...Small Craft Advisory until 8 PM EDT this evening for



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