Area Forecast Discussion
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FXUS61 KPBZ 220101

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

Quiescent conditions will continue through Tuesday morning.
Widespread showers and thunderstorms are expected on Tuesday as
a cold front crosses the region.


A rather pervasive cirrus shield has advanced eastward over
much of the CWA through the evening hours. Further, the earlier
diffuse dewpoint gradient has really become a non-factor. Thus,
with nighttime stabilization occurring, a lack of a
focusing/lifting mechanism, and convective blow off
overspreading the area, further convection development is
unlikely. PoPs have been limited to the north of I-80 realm for
the next few hours before the bulk of the overnight hours become

As convective blow off seems poised to remain over the area for
much of the night, lows will have difficulty dropping all that
far from the current readings. Thus, an above normal night looks
to be in store with soupy conditions. Fries


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.


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


A few scattered showers and thunderstorms will continue through
01Z or so near/north of I-80, and have included VCTS at FKL/DUJ
as a result. After these dissipate with the loss of daytime
heating, mainly high clouds are expected overnight. Fog does not
appear to be much of a threat given the warm overnight
temperatures which will not allow crossover values to be

As a cold front approaches on Tuesday, showers and thunderstorms
will become more numerous from late morning on. Hinted at flight
condition deterioration with VCTS and a drop to MVFR
visibilities at several terminals during the afternoon. IFR
conditions are certainly possible, as are strong wind gusts, but
timing will need to be refined. Expect prevailing winds outside
of convection to increase to gust to between 15 and 25 knots
out of the southwest during the afternoon.

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




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