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Area forecast discussion
National Weather Service Pittsburgh PA
629 PM EDT sun Jul 21 2019

Synopsis...
the approach and passage of a cold front will bring rain throughout
the day Monday. Drier cooler weather can be expected for the
remainder of the week.

&&

Near term /until 6 am Monday morning/...
the eve update featured cosmetic pop adjustments based on radar and
high res model trends.

Previous...
scattered and discontinuous convection continues along a very slow
moving and diffuse cold front stretching from approximately Coshocton
Ohio eastward towards Pittsburgh and into Westmoreland County PA. MLCAPE
values in the vicinity are in excess of 2500 j/kg for much of the
region. Combined with virtually no capping, storms should continue to
initiate along this boundary over the next few hours, despite little
in the way of upper forcing currently.

With steep low-level lapse rates and the presence of some mid-level
dry air, strong downdrafts / damaging wind gusts will be possible.
There is also a threat for localized flash flooding in urban or
other especially susceptible areas as storms train west to east
along the boundary.

Convective activity should initially wane a bit overnight as the
lower atmosphere stabilizes, though a few scattered showers are
still possible in close proximity to the frontal boundary.

Some convective-allowing models (cams) do suggest an uptick in
activity late overnight in association with some mid-level energy /
shortwave ahead of the main trough axis digging across the Ohio
Valley. Cloud cover and moist-low level air will keep temperatures
warm once again overnight. Lows will range from the mid 60s in the
vicinity of the I-80 corridor to mid 70s elsewhere.

&&

Short term /6 am Monday morning through Monday night/...
by Monday morning, storms will likely be ongoing along/near the
aforementioned frontal boundary. At this time, the cold front will
be stalled, bisecting the County Warning Area. Exact placement is somewhat uncertain
and will ultimately depend on the convective evolution overnight
tonight.

Impressive shortwave trough will dig into the upper Midwest Monday
evening and shift eastward overnight. This energy will push the
front southeastward, and it will reach the mid-Atlantic region by
early Tuesday morning. Showers will end from northwest to southeast Monday night.
Cooler and much less humid air will spread across the region behind
the exiting rain.

Precipitation amounts on Monday will vary from from around half an
inch in places north of Pittsburgh to possibly in excess of an inch
along/south of the Mason-Dixon line and also in locations that see
multiple storms move across.

&&

Long term /Tuesday through Sunday/...
cool, comparatively dry air will filter in behind the cold front on
Tuesday. A few lingering showers cannot be ruled out as cool air
moves over a Warm Lake Erie, but otherwise most locales will be dry.
Cloud cover will gradually decrease through the day as high pressure
builds into the region.

Seasonal or even slightly below seasonal temperatures are expected
across the area through much of next week. Temperatures will rebound
by the weekend as southerly flow returns and high pressure slides
off the Atlantic coast. Ensembles and blended guidance are showing a
dry long term.

&&

Aviation /00z Monday through Friday/...
brief MVFR/IFR restrictions are expected in any storm that passes
over a terminal with greatest confidence in the terminals between
I-70 and I-80 given latest hi res output.

Approaching shortwave trough will maintain shower chances, with
increasing coverage through Monday. Expect both ceiling and
visibility restrictions to continue until cold front crosses Monday
night.

Outlook...
VFR will return behind the cold front passage, with prevailing VFR
expected for much of the week, outside of any morning fog.

&&

Pbz watches/warnings/advisories...
Maryland...none.
Ohio...none.
PA...none.

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