Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 151755
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
155 PM EDT Tue Aug 15 2017

.SYNOPSIS...
A cold frontal passage will help to generate some showers and
thunderstorms into this evening, then high pressure over the Upper
Great Lakes will slowly cross by to our north. This will guarantee a
scintillating Wednesday across our region before more unsettled
weather arrives later Thursday and Thursday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
It will be an active afternoon across parts of the region...
particularly in a strip from Niagara and Orleans counties east to
Ontario county. In this area...roughly in an area bisected by the
New York State Thruway...showers and strong thunderstorms will
become rather common through 21z.

The large scale forcing for the thunderstorms will be a robust
shortwave that will pass by to our north. At 17z...this feature was
seen in WV imagery pushing east along the north shore of Lake
Ontario. Meanwhile...SBCAPE values across our region generally range
from 1000 to 1500 j/kg with 40 to 45 knots of bulk shear. This can
be at least partially inferred by the anomalously strong 100kt H25
jet that is cruising by just to our south.

Meanwhile on the mesoscale level...a convergence zone is in place
from IAG to ROC and this will help to focus a near stationary line
of convection that will feature training showers and thunderstorms.
This will heighten the risk for localized flooding from repeated
storms. There will likely be some pea sized hail with some
storms...and possibly wind gusts to 40 mph.

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 this afternoon will be a few degrees above mid August
norms...with 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 /18Z TUESDAY THROUGH SUNDAY/...
While VFR conditions will be in place across the region this
afternoon...there will be an increasing amount of showers and
thunderstorms. Any of the thunderstorms could briefly limit cigs and
vsbys to MVFR levels.

In the wake of a passing cold front and its associated convection
this evening...widespread VFR conditions will be in place across the
region. The exception will be across parts of the Southern Tier
where IFR conditions in fog and stratus will be likely after 08z.

High pressure moving over the area on Wednesday will produce
tranquil VFR conditions.

Outlook...
Thursday...VFR deteriorating to MVFR as showers and thunderstorms
increase later in the day and at night.
Friday...Mainly VFR with a chance of showers and thunderstorms.
Saturday...VFR.
Saturday night and Sunday...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...RSH
NEAR TERM...RSH
SHORT TERM...TMA
LONG TERM...RSH
AVIATION...RSH
MARINE...THOMAS



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