Area Forecast Discussion
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FXUS61 KPBZ 241910

Area Forecast Discussion
National Weather Service Pittsburgh PA
310 PM EDT Mon Jul 24 2017

A stagnant mid-level trough will keep very-humid conditions
over the region today with a continued threat for showers and
thunderstorms. Dry conditions are expected Tuesday through early


A moist, but weakly-unstable airmass remains this afternoon in
the sern quadrant of the forecast area ahead of an advancing
cold front. Showers and storms have developed in this unstable
airmass.  But morning cloud cover has limited the magnitude of
instability, with updrafts unable to overcome the moderate
shear. Storms should exit late this afternoon save for lingering
showers in the ridges and possibly coming off the lake.

Dry air and steep low-level lapse rates are leading to stratocu
advancing from the lakes across the region through the evening.
These clouds should clear by morning amid broad subsidence.


Upper-level heights will rise on Tue ahead of a shortwave
ridge, and broad surface high pressure will build into the
Great Lakes region. The drying boundary layer and overall
subsidence will support a dry, seasonable forecast for Tue/Wed.

Low-level moisture will begin to increase again Wed, which will
help maintain above-average minima despite light wind and
increasing cloud cover.


Models are consistent for Thu in digging a deep upper-level
trough along the Appalachians, which will act on an
increasingly-moist and unstable airmass as a cold front crosses
the region. Showers and storms along the boundary are highly
probable, and PoPs were increased to reflect this expectation.

The forecast for Friday into the weekend gets a bit muddy, as
the evolution of the upper trough varies among the medium-range
models. If the trough progresses sewd, then the weekend is
shaping up to be dry and sunny, with seasonable highs. But other
model solutions open the upper wave across the Appalachians,
keeping the threat for clouds and precipitation (especially
overaforementionedthe eastern ridges) into Friday and

With an amplified upper ridge persisting in the wrn CONUS, it is
likely that a mean trough will remain over the ern CONUS for the
better part of the extended forecast. The net effect will be
overall a seasonably-warm and -active weather pattern.


At 19Z, a broken line of showers and thunderstorms was located
from KDUJ-KAFJ-KPKB, with greatest coverage near MGW. MVFR
ceilings will linger across the area today. The slow-moving
boundary will sag south through the remainder of the afternoon.

By evening, VFR conditions should persist over the area.
Lingering low-level moisture may produce some restrictions in
the early morning hours Tuesday. Otherwise, VFR conditions are
expected through Wednesday.

VFR is expected to prevail through mid-week as high pressure
builds in. Moisture will return Thu ahead of a sewd-moving





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