Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 151022
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
622 AM EDT Tue Aug 15 2017

.SYNOPSIS...
A quiet morning will become active this afternoon as showers and
thunderstorms develop along lake breeze boundaries, and gradually
shift eastward. A weak cool front will cross the region tonight,
sweeping daytime showers and thunderstorms eastward, while bringing
slightly cooler and less humid air across the region for Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Water vapor imagery displays a shortwave passing across Michigan
this morning. Showers have developed across the western end of Lake
Ontario this morning, and this activity will brush by the Niagara-
Orleans county shoreline before dissipating by mid morning.

Otherwise, for this morning a partly to mostly sky will allow for
daytime instability to increase, nearing 1000 J/KG by early
afternoon. Meanwhile moisture pooling ahead of the upper level
shortwave will reach our region this early afternoon.

A southwest wind and lake breeze circulation will develop through
the morning hours, creating a low level convergent forcing mechanism
for when the upper level trough and a veering wind profile
approaches. As such we will likely see showers and thunderstorms
blossoming this afternoon both on a northern Lake Erie convergent
zone over the Niagara escarpment and in addition, the inland So.
Tier.

Wind shear will be greatest during the early afternoon, with 0-
6km wind shear of 40 to 45 knots providing enough tilt to the storms
to allow them to grow, possibly yielding small hail and gusty winds.
Will continue to mention this possibility this afternoon for
portions of WNY.

The upper level shortwave today will bring more broad scale lift
than yesterday...and as such expect activity in a better moisture
environment to be with more coverage area today than yesterday.
Still the bulk of the time today at any given point will be dry.

As we advance through the afternoon hours, the lake breeze showers
and thunderstorms will push eastward, across the Genesee valley,
finger lakes and to portions of areas east of Lake ontario this
early evening. There may be a few Lake Ontario lake breeze showers
and thunderstorms this afternoon though both moisture and low level
instability will not be as great as near Lake Erie.

This activity will diminish through the evening hours, and come to
an end with the passage of a cold front through the overnight hours.
Clearing skies behind the cold front, and lingering elevated
dewpoints may allow for river valley fog to form across the Southern
Tier tonight.

Temperatures today will be a few degrees above mid August norms,
with afternoon highs in the upper 70s to lower 80s. Tonight lows
will drop back to the upper 50s to mid 60s.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY NIGHT/...
High pressure will build in from southern Ontario on Wednesday.
Sunshine will mix with a few diurnal cumulus clouds, but overall
expecting mostly sunny conditions due to strong subsidence with the
incoming surface high. 850 mb temperatures in the 10C to 14C range
should support afternoon temperatures to near 80F over western New
York, ands mid 70s across the North country. Humidity levels will be
very comfortable with surface dewpoints in the 40s and 50s.

Fair and quiet conditions will continue Wednesday night as high
pressure remains in control. Overnight low temperatures away from
the lakes will generally be in the 50s, with some 40s possible
across portions of the Tug hill and western Adirondacks.

Changes will get underway Thursday as the area of high pressure
gradually pushes off to the east. Low pressure across the western
Great Lakes Thursday morning will deepen as it slowly progresses
northeastward Thursday evening. A warm air advection pattern will be
underway through most of the day, but really ramps up late Thursday
afternoon through early Thursday night. As a result, increasing deep
layer moisture and top-down saturation will lead to increasing
shower chances and perhaps a few thunderstorms from west to east as
we move through Thursday afternoon into Thursday night.

A cold front sweeps across western New York Friday. This will
maintain chances for scattered showers and possible thunderstorms,
especially east of Lake Ontario.

While a mid level cyclonic flow will be in place across the Great
Lakes, weak surface ridging in the wake of the front will combine
with a dry slot to provide a mainly dry Friday night.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
This should generally be a dry forecast period...especially from
the second half of the weekend into the start of the new work week.

On Saturday...the medium range guidance packages are in disagreement
with the placement of the next longwave trough. Will lean more
towards the ECMWF...which suggests that the base of a trough passes
across the Lower Great Lakes while pushing a frontal boundary over
the region. Will carry low chc pops for this low confidence forecast
while holding afternoon temperatures in the mid 70s for most areas.

Much better agreement is then found between the various packages for
Sunday and Monday. A large sfc high is forecast to build across the
Lower Great Lakes. This would provide us with fair weather...and
nearly ideal sky conditions for viewing of the solar eclipse here in
western New York. Stay tuned.

&&

.AVIATION /10Z TUESDAY THROUGH SATURDAY/...
For the 12Z TAFS fog across the So. Tier has reached KJHW, and this
fog and low stratus will linger through about 14Z. Otherwise VFR
flight conditions should prevail across the TAF sites today...with
the exception being a brief interruption in showers or thunderstorms.
This convection, forming initially on lake breeze boundaries will be
near KIAG/KBUF and KROC between 17Z and 21Z.

Southwest winds today will veer to westerly tonight, and diminish in
speed...while storms also diminish this evening. Clearing skies
tonight across the So. Tier will bring again chances for IFR or
lower flight restrictions in fog, including the KJHW terminal.

Outlook...
Wednesday...Local IFR in southern Tier valley fog early,
otherwise VFR.
Thursday...Areas of MVFR with showers and thunderstorms likely.
Friday and Saturday...Mainly VFR with a chance of showers.

&&

.MARINE...
A weak ridge of high pressure will remain across the Lower Lakes
through Wednesday night with light winds and minimal waves on the
lakes. A warm front will near the region Thursday, with showers and
thunderstorms, along with an southeasterly wind that will bring the
highest waves towards the Canadian waters.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...None.

&&

$$

SYNOPSIS...THOMAS
NEAR TERM...THOMAS
SHORT TERM...TMA
LONG TERM...RSH
AVIATION...THOMAS
MARINE...THOMAS



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