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000
FXUS61 KPBZ 212127
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
527 PM EDT Mon Aug 21 2017

.SYNOPSIS...
A sequence of weak upper-level disturbances will provide
isolated showers and thunderstorms today. Widespread showers
and thunderstorms are expected on Tuesday as a cold front
crosses the region.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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A weak dewpoint discontinuity currently traverses Indiana and
Ohio into NW PA generally along I-80. To the west, a weak short
wave trough is working down this boundary, helping to initiate
convection along it. This should last a few more hours as we are
generally right near peak heating at this time. This is
especially the case as we need to overcome the roughly 5 degrees
lost during the eclipse.

That said, a rather pervasive cirrus shield has advanced
eastward over much of the CWA to the south of this dewpoint
gradient, and that along with the weakened heating from the
eclipse has really been the death knell for cumulus
redevelopment. With dewpoints in the 70s and heating having
resumed, a few pop ups cannot be ruled out, however anything
organized seems highly specious as we get deeper into the
evening.

Convection should wave by later in the evening, however
convective blow off will likely yield a less than clear sky
through the balance of the night. Fries
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&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
A strong upper low will dig into the Great Lakes on Tue and
acquire a neutral to negative tilt through the day in concert
with the movement of a mid-level jet maximum. The system`s
associated cold front will approach the Ohio Valley during the
early evening, but a prefrontal trough is expected to be the
focus for daytime convection in the area.

Abundant low-level moisture, steepening lapse rates and strong
effective bulk shear will support the development of strong to
severe thunderstorms by early afternoon along the sharpening sfc
trough. CAPE on the order of 2000 J/kg and effective shear of
40-50kt will promote organized, severe convection.

Given the deep-layer shear orientation roughly parallel to the
sfc feature, storms should congeal quickly into an intense
convective line that will move sewd into the instability axis.
Damaging wind gusts will be the primary threat, but hail also is
possible in more intense, cellular updrafts ahead of the line.

Storms will exit sewd by early evening with rain lingering into
the evening behind the storms as the cold front traverses the
region. High pressure will build in on Wed/Wed eve, with little
chance of rain as dry air invades.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Although ensembles still show spread in their upper pattern
solutions, it appears that broad surface high pressure under an
ern-CONUS trough/midwestern ridge pattern is progged to support
a generally-dry air mass through the period. Daily temperatures
below climatological average can be expected through early next
week.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
General VFR is expected for the period although a crossing
shortwave may spawn isold to sct convection. Expect rapid
deterioration of conditions on Tuesday as widespread precip will
herald the advance of cold front.

.Outlook...
With passage of an early Wed cold front, general VFR can be
expected for the remainder of the week.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...None.
OH...None.
PA...None.
WV...None.

&&

$$