Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 280249
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
1049 PM EDT Tue Oct 27 2020

.SYNOPSIS...
A weak front pushing through the region tonight will generate a few
hours of light rain. While the rain will taper off to scattered
showers overnight...it will be somewhat widespread northeast of both
lakes into Wednesday morning. High pressure will then nose into the
area from the Ohio valley Wednesday afternoon and night. A storm
system will pass well to our south Thursday and Thursday night.
While this will produce some widespread rain for our region...it
could also support the first snowfall of the season.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
A mid level shortwave and associated weak cold front will cross the
Lower Great Lakes tonight. Associated DPVA and deeper moisture and
convergence along the frontal zone will produce a round of fairly
widespread rain for the Southern Tier through 1 AM or so. While
most of the forecast area will be pcpn free overnight, showers will
blossom northeast of both lakes.

Modest cold advection in the wake of the trough will drop 850MB
temps down to -2C to -4C overnight. This will allow lake induced
equilibrium levels to rise to around 7-8K feet. Well aligned flow
down the long axis of the lakes will support some lake response,
with bands of lake effect rain showers overnight. Off Lake Erie WSW
flow will direct this into the Buffalo Southtowns, and Off Lake
Ontario SW flow will direct this into Jefferson County. Forecast
soundings stay warm enough for all rain in most locations. The Tug
Hill Plateau may get just cold enough to support a few wet
snowflakes, but most of the lake effect precipitation will remain
north of that area and across lower elevations.

Lake effect rain showers will persist northeast of the lakes through
Wednesday morning. Off Lake Erie...the band of showers will be found
across the Buffalo Southtowns and possibly hugging the lakeshore of
Chautauqua County as well. Off Lake Ontario...most of the showers
will be across Jefferson County. The lake effect showers will end by
early afternoon as warm advection increases aloft, lowering lake
induced equilibrium levels to the point where lake effect can no
longer be supported. Otherwise for the rest of the area, surface
high pressure building east across Ohio and PA will bring dry
weather. It will turn breezy Wednesday, especially northeast of the
lakes where gusts of 30-35 mph are expected.

Wednesday night, a cold front will move south across Ontario,
reaching Lake Ontario by daybreak Thursday. Meanwhile the remnants
of Zeta will move towards the Ohio Valley. Our region will remain in
the squeeze play between these two systems, with mainly dry weather.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
A very complex pattern evolution will unfold Thursday through Friday
as the remnants of Zeta become involved with a mid-latitude frontal
zone. Model guidance is in fairly good agreement overall with the
synoptic pattern evolution, but small run to run changes in track
and thermal profile details will continue to make this period a
challenging forecast.

The remnants of Zeta will quickly become extratropical and race from
just south of the Ohio Valley Thursday morning to off the Jersey
Shore by Thursday evening. Meanwhile a mid-latitude frontal zone
will be drifting south, with associated frontogenesis, deformation,
and upper level jet dynamics resulting in an expansive precipitation
shield to the north of the remnants of Zeta. Model guidance over the
past 24 hours has trended just a little south, and also less
aggressive in terms of snow potential for our area with slightly
warmer forecast soundings.

Looking at the details, rain will reach the western Southern Tier
Thursday morning, then spread slowly north and east to near the
south shore of Lake Ontario by late Thursday. Widespread
precipitation will continue through the first half of Thursday night
south of Lake Ontario, then taper off from northwest to southeast
late Thursday night and early Friday morning.

Colder air will filter in from the north as low level northeast
winds increase in response to strengthening high pressure over
Ontario and Quebec. This will allow for rain to mix with and change
to wet snow towards the end of the precipitation event. Wet snow,
possibly still mixed with a little rain will then quickly taper off
Friday morning as the system pulls away. It will become cold enough
for a lake response Friday on northwest flow, but a rapidly drying
airmass will be difficult to overcome. This setup will only support
a few scattered wet snow and rain showers Friday south and southeast
of the lakes, ending later in the day. With the farther south track,
the North Country may escape with very little precipitation.

As far as potential snow accumulations go, given the farther south
and somewhat warmer model trends over the past 24 hours, this
appears to be a minor event. The best chance for any minor
accumulations will be across the higher terrain of the Southern Tier
and the Bristol Hills, with a much lower chance across the lake
plains along and north of the Thruway. Model trends will continue to
be closely monitored however.

Friday night skies will clear as strong high pressure builds into
the eastern Great Lakes. This will set the stage for the coldest
night so far this fall season, with lows well down into the 20s in
most locations, and some teens across the Southern Tier and North
Country.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
Strong high pressure will remain in place over the Lower Great
Lakes and New England Saturday, allowing for plenty of sunshine
across the region. After a very cold start, temperatures will
recover into the mid to upper 40s in Western NY, and low to mid
40s east of Lake Ontario.

The next upper level trough and associated cold front is expected to
track across the Great Lakes Sunday. The trough will sharpen over
the Great Lakes by late Sunday, with the cold front reaching the
eastern Great Lakes in the afternoon. This will bring increasing
clouds and a chance of a few rain showers, especially in the
afternoon.

Behind the cold front Sunday, cold advection will bring a return to
below normal temperatures Sunday night and Monday. WNW flow and wrap
around moisture may support some broad lake effect rain and snow
showers Sunday night through Monday morning, especially southeast of
the lakes.

Forecast uncertainty increases somewhat by Monday afternoon and
Tuesday. A wave of low pressure and mid level trough pass to the
north across Canada Monday evening into Tuesday. The ECMWF and
Global GEM are stronger and farther south with this feature than the
flat wave depicted by the GFS. If the stronger solutions verify, a
fresh batch of cold air would arrive later Monday into Tuesday with
a few more lake effect rain and snow showers east and southeast of
the lakes. For now, kept low chance POPS through this period.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Widespread MVFR cigs will be found across the region tonight...with
IFR cigs anticipated across the Southern Tier and for a few hours
east of Lake Ontario. While the low cigs will be accompanied by some
light rain...the bulk of the pcpn after 05z will be focused
northeast of both lakes in the form of lake effect rain. It is not
out of the question that the rain is mixed with wet snow at KART and
KGTB.

On Wednesday...the day will start with fairly widespread MVFR cigs.
As we progress through the morning into the midday...cigs will
gradually improve to VFR levels. Wednesday night will feature mainly
VFR conditions.

Outlook...

Thursday...Mainly VFR deteriorating to MVFR/IFR with rain
developing, especially southern portions of the area.
Thursday night...MVFR/IFR with rain, possibly mixing with or
changing to wet snow.
Friday...MVFR/IFR with wet snow or rain showers tapering off in
the morning, improving to VFR/MVFR.
Saturday...VFR.
Sunday...VFR/MVFR with a chance of showers.

&&

.MARINE...
Winds will remain relatively light through tonight with a weak
pressure gradient across the eastern Great Lakes. High pressure will
build south of the area Wednesday, allowing for stronger west to
southwest winds to develop. This will support a round of Small Craft
Advisory conditions on Lake Erie and at least the northeast portion
of Lake Ontario. Winds will then diminish later Wednesday night.

Low pressure will move from the Ohio Valley to off the northern Mid
Atlantic Thursday through early Friday. A period of stronger
northeast winds will develop on the eastern Great Lakes as a tight
pressure gradient develops between this low and high pressure
building into Ontario and Quebec. This will bring another round of
Small Craft Advisory conditions staring Thursday afternoon and
lasting through Friday morning.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from noon to 11 PM EDT Wednesday for
         LEZ040-041.
         Small Craft Advisory from noon Wednesday to 2 AM EDT
         Thursday for LOZ045.

&&

$$

SYNOPSIS...RSH
NEAR TERM...Hitchcock/RSH
SHORT TERM...Hitchcock
LONG TERM...Hitchcock/PP
AVIATION...RSH
MARINE...Hitchcock/RSH


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