NWS Area Forecast Discussion

000
FXUS61 KBUF 180243
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
943 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 will slide to our east while the an 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 rain into
far western New York between 4am and 6am. Expect temps to lower
this evening before southerly flow yields steadily rising temps
for the balance of the night. Across far western New York, this
will result in evening lows in the lower to mid 30s giving way
to readings in the upper 30s to lower 40s by daybreak, while
further east evening 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.

Regarding the freezing rain threat east of Lake Ontario on
Saturday AM...precipitation should hold off long enough for
temperatures to rise above freezing while the lower airmass
slowly saturates. With this in mind, have backed off the
freezing rain threat except for over Lewis County. May have to
wait until Saturday before it becomes obvious for or against a
freezing rain threat. Any threat would be short-lived and last
at most an hour or so.

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 rising surface temperatures and widespread rain
spreading from western into central New York. 850mb temps increasing
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 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
probably come in several waves, with the first arriving in the
AM, possibly followed be a break for a few or several hours.
Heavier periods of rain will arrive later Saturday afternoon in
the western Southern Tier where the low level jet strengthens
ahead of an approaching cold front. Winds will not be 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 /03Z SATURDAY THROUGH WEDNESDAY/...
An elongated ridge of high pressure will slide off to our east while
the an area of low pressure tracks toward Chicago and continues
organize. Expect VFR conditions to continue overnight under
widespread mid and high cloud cover. Winds aloft increase
overnight out ahead of the approaching low, LLWS is expected WNY
TAFs (KBUF/KIAG/KJHW/KROC) 8-12z.

Rain is expected to reach far western New York (KBUF/KIAG/KJHW)
by 9-10z with lowering cigs to MVFR/IFR by 12z Saturday. There
may be several waves of rain, with a few or several hours of dry
weather in between, but overall CIGS will continue to show a
slow lowering trend. MVFR to IFR cigs will linger through the
day Saturday with widespread rain, steadiest and heaviest toward
the Southern Tier by late afternoon.

Outlook...

Saturday night...Rain changing to snow...and becoming windy.
Sunday-Monday...Lake effect SN, IFR SE of lakes, otherwise VFR/MVFR.
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 will bring a
period of gale force winds to Lakes Erie and Ontario Saturday
night and Sunday behind a cold front.

&&

.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 Warning from 10 PM Saturday to 7 PM EST Sunday for LEZ040-
         041.
         Gale Warning from 1 AM to 10 PM EST Sunday for
         LOZ042>045-062>065.

&&

$$

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

NWS BUF Office Area Forecast Discussion