Area Forecast Discussion
Issued by NWS Buffalo, NY

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000
FXUS61 KBUF 172106
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
406 PM EST Fri Nov 17 2017

.SYNOPSIS...
High pressure shifting across our region will continue to provide a
brief return of fair weather into tonight. Saturday, a strong
storm system will track across the region with a round of
widespread rain and gusty winds. This will be followed Sunday by
colder temperatures and accumulating lake snows southeast of
the lakes.

&&

.NEAR TERM /THROUGH SATURDAY/...
High pressure is centered over western NY this afternoon. Subsidence
brought on by the high pressure and dry air advection has completely
cleared out the low clouds south of the eastern Great Lakes. Partly
to mostly sunny skies will be in place for most through this
afternoon with mid and high clouds starting to arrive from our west
ahead of a slowly organizing storm system over Kansas. Some radar
returns across Michigan this afternoon are expected to dissipate
before reaching western NY as they shift into the back of the slowly
departing high pressure. Temperatures remain slow to warm today with
cold advection. Most areas will see highs range from the mid to
upper 30s with a few spotty 40s today.
The higher terrain of the North Country will remain the low to mid
30s.

Tonight, high pressure will slide to our east while the
aforementioned area of low pressure begins to strengthen while
tracking to near Saint Louis. A warm front ahead of this storm will
shift into the Ohio Valley. Much of our area can expect fair/dry
weather to prevail for most of the overnight although under
widespread mid and high cloud cover ahead of this system. Late
tonight, moisture transport and lift brought on by a low level jet
oriented with the warm front will bring bring rain into far western
New York between 4am and 6am. Have speed up the timing an hour or
two based on 12z guidance. Expect temps to cool this evening before
southerly flow yields steadily rising temps for the balance of the
night. Across far western New York, this will result in lows in the
lower to mid 30s giving way to readings in the upper 30s to lower
40s by daybreak while further east lows in the 20s will give way to
temps in the 30s by the start of Saturday morning.

Expect that surface temps will be above freezing for nearly all
locations before the rain arrives late tonight into early Saturday
morning. There is just a slight/low chance that across the interior
North Country, away from Lake Ontario, temps may still be at or just
below freezing when the leading edge of the rain arrives. This has
led to a chance of freezing rain possible for an hour or two.
Confidence remains below 50% however do to slight but still
important in this case differences of when the models bring in the
rain. An hour faster would lead to a higher probability for some
limited freezing rain, while an hour slower would yield just plain
rain.

Saturday, Model consensus tracks the feature surface low across
Illinois/Indiana to near or just north of Lake Erie while deepening
to the vicinity of 990mb. Strengthening southerly flow ahead of
this will promote warming surface temperatures and widespread rain
spreading from western into central New York. 850mb temps warming to
between +3C (north country) and +8C (western SoTier) would normally
support high temps pushing into the 60s but with widespread rain,
expect that evaporational cooling and wetbulbing will only support a
high of low 50s in WNY and mid 40s in the North Country. PWATs of
between 0.75 and 1 inch is a slight positive anomaly for this time
of year with model consensus QPF yielding a healthy 0.75-1 inch for
WNY with 0.25 to 0.5 inch across CNY through 7pm Saturday. Rainfall
will become heaviest toward Saturday afternoon in the western
Southern Tier where the low level jet strengthens ahead of an
approaching cold front. Winds will not be too gusty through the day
as warm advection keeps the higher winds aloft from mixing down.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
Winter headlines may be needed during this period, as a
transition to accumulating lake snows takes place southeast of
both lakes.

Deepening surface low pressure is expected to track just to the
north of the region Saturday night, which will swing a powerful
cold front through the area. Deepening cold air behind the cold
front will set the stage for some mixed lake effect precipitation
east of both lakes. There could even be a coating of wet snow
along the Boston Hills and Chautauqua ridge and Tug Hill region.

Winds will ramp up within the cold air advection pattern.,
especially Sunday. Momentum transfer profiles suggesting 45 to
55 mph wind gusts at best, with the highest wind gust potential
confined to the immediate shorelines of Lake Erie and Lake
Ontario.

A cold cyclonic flow of air will continue across the lower Great
Lakes Sunday into Monday. This will set the stage for lake
effect snows southeast of the lakes in a northwest flow regime.
Over-lake instability certainly looks outstanding with profiles
suggesting moderate to extreme instability developing with lake
induced CAPES over 500 J/KG and inversion heights very
respectable. However, the synoptic moisture fields are far from
outstanding with omega displaced below favorable dendritic
growth zone combined with less than ideal shear profiles all
would suggest this lake effect event likely be a plowable, but
not significant snowfall from the southern Tug Hill over to
east of Rochester off Lake Ontario and the Chautauqua ridge and
Boston Hills off Lake Erie.

Lake effect snows will begin to diminish off of both lakes Monday
in response to a ridge of high pressure quickly building in
across the lower Great Lakes, which will effectively limit
synoptic moisture and lower the capping inversion. As the ridge
builds in, the steering flow will slowly pivot the weakening
snow bands northward toward Buffalo and into the Tug Hill before
ending by Monday evening.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
A shortwave trough will dip across the Eastern Great Lakes region
this period, with several additional shortwaves maintaining a deeper
long wave trough over the region through the holiday.

Sunshine Tuesday will fade through the day as a cold front nears the
region...with the cold front bringing a mix of rain and snow Tuesday
night, changing to all snow later Tuesday night and Wednesday as
deeper colder air (-10C/850 hPa) builds over the eastern Great
Lakes. This colder air will generate lake instability with details
of how much moisture and wind direction to still be resolved
relating to lake effect snow potential for Wednesday-Thursday.

Another frontal boundary will likely dip southward from Canada
Friday...maintain chances for snow, especially across Lake Ontario
and points eastward which at this time will be closer to the frontal
boundary.

Temperatures Tuesday will be above normal...but expect at or below
normal temperatures the remainder of the forecast period.

&&

.AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
High pressure over our region and associated subsidence and dry air
advection have scattered out the previous MVFR stratus leaving
behind VFR conditions. Mid and high clouds will then increase from
the west through this afternoon out ahead of a slowly organizing
storm system over the Central Plains states.

Tonight the elongated ridge of high pressure will slide off to our
east...while the aforementioned area of low pressure tracks toward
Chicago and continues to slowly get better organized. Expect VFR
conditions to continue for much of the night under widespread mid
and high cloud cover.

Rain is then expected to reach far western New York (KBUF/KIAG/KJHW)
by 9-10z with lowering cigs to MVFR/IFR by 12z Saturday. As winds
aloft increase overnight out ahead of the approaching low, LLWS is
also expected at all western TAFs (KBUF/KIAG/KJHW/KROC) 8-12z.
MVFR to IFR cigs will linger through the day Saturday with
widespread rain.

Outlook...

Saturday night...Rain changing to snow...and becoming windy.
Sunday and Monday...Lake effect snow and attendant IFR
southeast of the lakes...otherwise VFR/MVFR with scattered snow
showers.
Tuesday...Mainly VFR.
Wednesday...Rain and snow showers with a chance of MVFR/IFR.

&&

.MARINE...
High pressure over Lake Ontario will continue a short period of sub-
advisory-level conditions this afternoon into tonight.

As we move on into the weekend...a strengthening storm system will
track northeast across the Great Lakes. This may bring a period of
gale force winds to Lakes Erie and Ontario Saturday night and Sunday
behind a cold front. Accordingly...Gale Watches have been hoisted as
outlined below.

&&

.TIDES/COASTAL FLOODING...
Developing very strong onshore winds will build significant wave
action from late Saturday night into Sunday night along the
Lake Ontario shoreline. The combination of already higher lake
levels and continued 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 Watch from late Saturday night through late
     Sunday night for NYZ001>007.
MARINE...Gale Watch from Saturday evening through Sunday afternoon for
         LEZ040-041.
         Gale Watch from Saturday evening through Sunday
         afternoon for LOZ042>045-062>065.

&&

$$

SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...TMA
LONG TERM...THOMAS
AVIATION...SMITH
MARINE...SMITH
TIDES/COASTAL FLOODING...TMA


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