Area Forecast Discussion
Issued by NWS Pittsburgh, PA

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FXUS61 KPBZ 151438

Area Forecast Discussion
National Weather Service Pittsburgh PA
1038 AM EDT Wed Jul 15 2020

Dry hot weather is expected today. Shower and potentially severe
thunderstorm chances return Thursday through Friday with a trough of
low pressure.


Increased ridging in response to a digging Midwest trough should
support prevailing warm and dry conditions through the period. Warm
advection and rising 500 mb heights should result in high temperature
from the upper 80s to around 90 for locations outside of the higher
terrain, or on the order of 5 to 8 degrees above calculated normals.

The ridge axis will propagate eastward tonight in response to the
encroaching trough, with a swly flow regime further advecting warm,
moist air into the region. The result will be increased dewpoint
values into the mid 60s tonight, with temperature remaining above


By Thursday morning, cont`d srly flow should persist warm, moist
advection ahead of a leading shortwave trough. As warming ensues,
forecast soundings suggest the development of sfc based instability
by midday, with dewpoint values surging into the upper 60s to near 70
degrees. Steep lapse rates should support modest CAPE values ahead
of the encroaching disturbance.

Though timing in high res. models vary, the general consensus
suggests an initial wave of convection developing during the early to
mid afternoon hours as shortwave ascent combined with favorable jet
support is realized. With DCAPE values over 1000 J/kg, PWAT values
exceeding 1.5 inches, and sufficient shear through a veering wind
profile, the result should be clusters of tstms capable of producing
hail, damaging wind, and isolated tornadoes. Adequate steering flow
should maintain rather progressive convection. However; modest PWAT
values within a deep, warm cloud layer may lead to efficient rainfall
in stronger tstms, with potential for localized flooding in urban
and poor drainage areas or areas where training storms are observed.
The SPC has maintained the region under a slight risk for severe
convection and potential hazards have been mentioned within the
Hazardous Weather Outlook.

A break in convection is then anticipated as mid level shortwave
ridging develops in the wake of the exiting shortwave. However;
additional forcing for ascent in association with an approaching cold
front and sfc low should yield another round of showers and tstms
Thursday night through Friday. Forecast soundings suggest additional
severe potential should be largely hampered with this second wave
given aforementioned ridging and unfavorable timing, maintaining
elevated instability through early Friday.

Neutral temperature advection in westerly flow in the wake of the
cold front passage will support slightly cooler, yet continued above
average high temperature on Friday. Large scale precipitation should
generally end as sfc high pressure builds through Friday evening.


Model ensemble solutions continue to indicate an upper high
persisting across the southern half of the CONUS through the period.
Relatively weak shortwaves are progged to periodically cross the
Upper Ohio Valley region on the northern periphery of the high. These
waves, along with diurnal instability, should lead to scattered
showers and thunderstorms across the region, especially during the
afternoon and evening. Hot weather should continue under this
pattern, with temperatures remaining 5 to 10 degrees above seasonable


VFR conditions are expected to prevail through the TAF period, with
light S/SE wind. Patches of high clouds will be prevalent, although
isolated to scattered cumulus are expected this afternoon.

Precipitation chances return after 12Z ahead of an approaching
front. A shower cannot be totally ruled out at PIT prior to 18Z, but
chances are too low to include in the 30-hour TAF at this time.

Restriction and convection potential returns with the approach of a
weak front on Thursday.




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