Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 160238
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
938 PM EST Wed Nov 15 2017

.SYNOPSIS...
A cold front will bring a few hours of rain across the region
tonight. Behind the front, some lake effect rain and higher
elevation snow will move in for Thursday. But, precipitation
will be ending just as the air becomes cold enough for more
widespread snow across Western and Central New York. Friday will
be rather quiet. Another storm system will reach the region for
the weekend, and bring rain and gusty winds on Saturday,
followed by temperatures that will allow for accumulating but
localized lake effect snow on Sunday.

&&

.NEAR TERM /THROUGH THURSDAY/...
A few lines of rain are moving into and eastward across WNY this
evening. So far, rainfall has been more like sprinkles as the
boundary layer slowly saturates, but eventually expect some
measurable rain overnight - a few hundredths to 1/3". The rain
is well ahead of a pair of cold frontal boundaries roughly tied
to maturing cyclone with surface low over the northern Great
Lakes region this evening. The upper level PV anomaly has
already caught up and passed the 999mb surface low, so expect minimal
to no additional deepening overnight as the system begins to
occlude. As temperatures slowly drop overnight, some higher
elevation areas may see a mix of rain and snow toward the Tug
Hill Plateau, otherwise just rain is expected.

Toward morning, the cold front will sweep across the region,
and cooler air will move across the Eastern Great Lakes with
temperatures at 850 hPa dropping to -2 to -4C. This will be cool
enough for a lake effect rain response into Thursday morning.
Initially, with the main upper level trough still to our west,
plumes of mainly rain will be oriented SW to NE.

Later Thursday, expect the lake effect rain to move southward,
and possibly mix with and change to snow as temperatures
throughout the column continue to drop. A slushy inch or so will
be possible on the hill tops of SW NYS and over the southern
Tug Hill. Lake induced equilibrium levels peak Thursday early
afternoon. But, then expect falling inversion heights and an
influx of drier air to cause lake effect precipitation to weaken
east of Lake Erie toward the end of the day. East of Lake
Ontario, favorable lake parameters should maintain a decent band
of precipitation southeast of Lake Ontario through the
afternoon.

Winds will also increase Thursday as a secondary trough drops
southward across Lake Ontario. Within the cold air advection
regime, a LLJ will develop with the GFS the most bullish and
showing wind speeds of up to 40 knots. The core of the LLJ will
likely mix down to the surface with steeping lapse rates within
the cold air advection, As a result, northwest gusts upwards to
40 mph will be possible along the southern and southeastern
shoreline of Lake Ontario. It will be gusty elsewhere, with
25-35 mph gusts across the remainder of the CWA.

Temperatures Thursday will remain fairly steady through the
day, with highs peaking in the low to mid 40s, with several
areas across SW NYS likely to remain in the upper 30s.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Any lingering lake enhanced / upslope enhanced showers southeast of
the lower Great Lakes Thursday evening will quickly diminish
overnight as high pressure, subsidence, and much drier air builds
into the region. The upper-level ridge axis will shift across the
region during the day Friday, ensuring a precipitation-free day.
Some weak warm advection will begin in western NY late in the day as
the ridge axis starts to shift to our east, but it will be a bit too
late in the day to help our high temperatures much. The subsidence
inversion will help keep our daytime highs limited to the 30s on
Friday, with a few low 40s in far SW NY.

As the surface high moves off the east coast Friday night, and warm
advection increases ahead of the next approaching weather system,
expect to see increasing cloud cover from west to east along with a
few showers into western NY by daybreak Saturday. Low temperatures
in western NY will occur early in the night (low 30s), before
increasing cloud cover, warm air advection, and downslope winds help
temperatures rise overnight into the low 40s.

A strong low pressure system will impact the region over the
weekend, bringing widespread rain Saturday, the possibility of
strong winds late Saturday into early Sunday, and lake effect snow
showers Sunday into early Monday. The storm will evolve from
the upper-level low seen on WV satellite imagery off the Pacific
northwest coast today. This wave will move across the Rockies,
resulting in lee side cyclogenesis on Friday, before tracking
through the central Great Lakes Saturday.

During the day Saturday, widespread rain will move across the region
as we become optimally placed under the nose of a strong low-level
jet and moisture advection plume into the developing warm frontal
boundary. QPF amounts will likely range from a half inch to an inch,
and should be well within the manageable range for the area creeks
and rivers. Temperatures will likely surge into the lower 50s across
the lake plains from the combined warm advection and downslope flow,
with some upper 40s inland across the higher terrain.

The upper-level PV max will track nearly directly over the lower
Great Lakes late Saturday, while the surface low will track from
about Detroit to Toronto to Ottawa. This surface low track is
slightly too close to the forecast area, with a bit too much
eastward motion for a classic high wind event, in which strong
SWerly wind develop behind the cold front. In this case, westerly
winds develop behind the cold front passage, which would be atypical
for a western NY high wind event. Instead, expect the strongest
winds will peak across Lake Ontario, as forecast models suggest well
aligned westerly flow with strong cold advection, steep lapse rates
and subsidence across the lake under the upper-level PV max. Will
have to keep an eye on any high wind potential downwind of Lake
Ontario from Oswego County funneling into the Mohawk Valley for late
Saturday, with the potential for wind advisory level gusts across
the rest of the lake plains.

Lake effect will begin to develop later Saturday night as colder air
pours into the region. There may still be some rain mixed in
Saturday night through the first half of Sunday before enough cold
air arrives to support a full change to snow Sunday afternoon.
Forecast models continue to suggest this will be a primarily
northwest flow lake effect event, which will focus snowfall southeast
of the lakes. Off of Lake Erie this would likely result in fairly
unorganized multibanded plumes across the far western Southern Tier.
Off of Lake Ontario, snowfall would likely be focused from Rochester
east to Syracuse, with the potential for an upstream lake connection
from the Georgian Bay or Lake Huron, which could help to boost
snowfall totals Sunday night. However, between the northwesterly
flow, less synoptic moisture to work with than previously model runs
suggested, and high pressure building in more quickly Monday,
accumulations may only be on the light to moderate side.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
A west-northwest flow lake effect snow event will be ongoing off
both lakes by Sunday night. Continued influx of cold air aloft will
create moderate to extreme over-lake instability with lake
induced CAPES over 500 J/kg and Equilibrium Levels over 10K
feet. Despite favorable instability parameters this lake effect
event is no slam dunk by any means. Still some concerns to depth
of available synoptic scale moisture. Shear profiles showing
more of a multi-banded event with bands tending to shift
around. Profiles also suggesting that omega will be a bit
displaced from the favorable dendritic growth zone. All this
could suggest more of a light to moderate snowfall event rather
that a more significant event. These questions should be
answered the coming days on how things start to align for
accumulation potential.

The lake effect snow will wind down during Monday as upper trough
shifts east of the area allowing as a warm advection pattern to set
up. A bubble of high pressure will work into the region with mainly
dry weather expected Monday night and Tuesday.

Next shortwave trough is forecast to amplify as it heads toward the
Great Lakes. This system will eventually push a strong cold front
across the region at some point Tuesday or Tuesday night. Behind the
front the air mass is plenty cold enough to generate another round
of lake effect snows. This time period will need to be monitored
closely especially considering the impact it could have on holiday
travel.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
VFR flight conditions will deteriorate to MVFR/IFR as a band of
rain showers advances across the region overnight.
Precipitation should be all rain and last about 2-3 hours.

Colder air behind a cold front will allow for the development of lake
effect plumes of rain late tonight and into Thursday. Initially,
bands will be near KBUF/ART and drop southward through the day.
Temperatures will be marginal for snow, though a little light
snow may fall across KJHW Thursday morning.

Within the cold air advection winds will veer to westerly and
increase in speed, with gusts upwards to 25 knots possible across
the airfields.

Outlook...

Thursday night...Rain/snow with localized IFR/MVFR ending.
Friday...VFR.
Friday night...IFR/MVFR with rain. LLWS also possible.
Saturday...Windy with MVFR in rain.
Sunday...Lake effect snow/IFR SE of the lakes. Otherwise VFR.
Monday...Lake effect snow/IFR SE of the Lakes. Otherwise VFR.

&&

.MARINE...
Southwest winds will increase tonight ahead of a cold front, with
Small Craft Advisories developing on Lake Erie, the upper Niagara
River and also the eastern waters of Lake Ontario tonight. Behind a
cold front winds will veer to west and northwesterly, while
increasing in speed. This will bring SCAs to both Lakes, as
well as the entire stretch of the Niagara River where a
northerly component Thursday afternoon.

Winds Thursday afternoon will increase to 30kts as a secondary
trough drops towards Lake Ontario. There is a chance that gales
could develop on Lake Ontario. For now will place this chance
in the HWO.

After a brief period of calmer conditions Friday afternoon, another
period of gusty winds looks likely this weekend as a stronger
storm system tracks northeastward across the Great Lakes.

&&

.TIDES/COASTAL FLOODING...
Northwest winds will develop Thursday behind a cold front
passage, with wind speeds increasing through the afternoon and
early evening hours. This will build water levels and wave
action along the entire Lake Ontario shoreline Thursday
afternoon into Friday morning. The combination of already higher
lake levels and added wave action will result in increased
shoreline erosion, especially where the lakeshore is already
unstable from erosion earlier in the year.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lakeshore Flood Warning from 1 PM Thursday to 7 AM EST Friday
     for NYZ001>007.
MARINE...Small Craft Advisory until 4 AM EST Friday for LEZ040-041.
         Small Craft Advisory until 4 PM EST Thursday for LEZ020.
         Small Craft Advisory from 3 PM Thursday to 4 AM EST
         Friday for LOZ030.
         Small Craft Advisory until 10 AM EST Friday for LOZ043-044.
         Small Craft Advisory until 7 AM EST Friday for LOZ042.
         Small Craft Advisory until 10 AM EST Friday for LOZ045.

&&

$$

SYNOPSIS...THOMAS/ZAFF
NEAR TERM...THOMAS/ZAFF
SHORT TERM...CHURCH
LONG TERM...TMA
AVIATION...THOMAS/ZAFF
MARINE...JJR/THOMAS/ZAFF
TIDES/COASTAL FLOODING...THOMAS



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