Area Forecast Discussion
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FXUS61 KPBZ 231915

Area Forecast Discussion
National Weather Service Pittsburgh PA
315 PM EDT Sun Jul 23 2017

A stagnant mid-level trough will keep very humid conditions over
the region through Monday with a continued threat for showers
and thunderstorms. Dry conditions are expected through early
Thursday before a cold front approaches from the northwest.



12Z KPIT sounding showed an uncapped environment with a narrow,
skinny CAPE profile and abundant lower tropospheric moisture. It
should be of no surprise to anyone that shower/thunderstorm
activity has been spatially randomized and overall weak, given
the lack of instability, poor daytime heating and an easily
forced environment. Two MCVs evident in satellite imagery loops,
one presently moving across SW PA and the other over central OH
have been the primary focal points for the shower and limited
storm activity until this point.

A more noteworthy feature has been the quasi-stationary front
that has been sitting roughly 30 miles southeast of the Erie
lake front and part of a much longer boundary. Stronger daytime
heating has occurred up across nrn OH/PA, with wind vectors
showing modest convergence into a narrow line of moderate
cumulus. High cirrus is also evident of an upper jet streak in
this region. Thus, the thought is that ongoing activity along
the I-70 corridor will continue to struggle amidst poor lapse
rates and negligible daytime heating. Rather, the focus for the
afternoon should be across northern OH into NW PA along the
aforementioned boundary beneath the upper jet streak. Although
cells should generally move ENE parallel to the boundary,
collective outflow should begin to force the front southward
with time. Even in this region I am not anticipating much in the
way of organized severe weather given modest CAPE, poor lapse
rates and marginal deep layer shear. The threat of severe storms
would therefore be restricted to wet microbursts, requiring the
merging of several longer lived cells to get sufficient water
loading. Something to keep an eye on this afternoon.

So far, activity has been moving east at 30-40 mph, and this
setup is not conducive to training, so any flood threat would be
very localized. Since the focus through this evening is not
where previous rain has fallen, think this threat is limited.



Do not anticipate much diurnal cooling early given mid 70s
dewpoints, so showers/storms should maintain intensity through
the evening, exiting the CWA prior to 06Z. Areas of locally
dense fog expected later tonight as skies gradually clear.

Mid level trough sweeps through Monday afternoon so this will
be the last round of showers/storms before a welcome break

Upper level heights will rise on Tuesday, and a broad surface
high will build into the Great Lakes. This will finally bring a
stretch of dry weather and sunshine for Tues/Wed.



A deep upper trough and associated surface cold front will
settle south from Ontario on Thursday, bringing the threat for
showers/storms during the afternoon and evening.

Forecast for Friday into the weekend gets a bit muddy. If the
aforementioned wave progresses into the Southeast, then the
weekend is shaping up to be spectacular with dry conditions and
highs around 80. Some model solutions open the upper wave up
across the Appalachians keeping the threat for clouds and
precipitation (especially over the eastern ridges) into Friday
and perhaps Saturday.


Cigs will continue to improve through the remainder of the
afternoon, with VFR expected to prevail, outside of any
thunderstorm. Morning cloud cover may have limited instability
initially but with clouds beginning to scatter out, coverage
should increase, as is progged by the hi res model guidance
this evening. Will keep the VCTS mention through tonight as the
upper level shortwave digs across the great lakes.
Deterioration back to MVFR and possibly IFR is expected, with
the late showers/storms with some improvement by early Monday as
the frontal boundary finally starts to sag southward across the
forecast area, some additional thunderstorm activity is
anticipated this evening. Kept VCTS in there with the

Restrictions will continue through Monday, with VFR prevailing




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