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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1220 AM CDT Sun Aug 21 2022

Valid 211200Z - 221200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS CENTERED OVER
PORTIONS OF THE MID AND UPPER OHIO AND TENNESSEE VALLEYS...

...SUMMARY...
Isolated strong to severe thunderstorms will be possible today
across parts of the Mid and Upper Ohio and Tennessee Valleys.

...Synopsis...
An upper trough is forecast to advance slowly eastward across the
eastern half of the U.S. today, while ridging prevails across the
interior West.  A short-wave trough over the eastern Pacific will
progress toward -- and eventually reach -- the Pacific Northwest
Coast, though its progression will be slowed by the prevailing
ridge.

At the surface, a weak cold front is forecast to cross the
Ohio/Tennessee/Mid Mississippi Valleys through the day, while the
trailing portion of this boundary lingers across Texas through the
period.

...Mid and Upper Ohio and Tennessee Valleys...
Diurnal heating of a moist low-level pre-frontal airmass will result
in afternoon destabilization, with mixed-layer CAPE expected to
average 1000 to 2000 J/kg across the Ohio/Tennessee Valleys.  Modest
ascent -- focused near the surface front -- in tandem with the
destabilizing environment will result in an increase in
coverage/intensity of ongoing storms, as well as new storm
development.  The initial convective increase is expected across the
Mid Ohio Valley region, but should eventually continue southwestward
across the Tennessee and into the Mid Mississippi Valleys through
the afternoon and into the early evening.

With moderate/cyclonic mid-level westerlies associated with the
upper trough spreading across the region, occasionally stronger
updrafts are expected, yielding mainly multicell organization. 
Damaging wind gusts will likely be the primary severe risk, which
should peak in the late afternoon but will likely linger well into
the evening in some areas.

...Central and southern Arizona...
As the airmass across central Arizona heats/destabilizes through the
afternoon, storm development is expected -- particularly in the
vicinity of the Mogollon Rim.  Models suggest some enhancement to
northerly/north-northeasterly flow in the 700 to 500 mb layer across
the area into the afternoon and evening, which may favor southward
propagation off the higher terrain into the lower deserts.  Some CAM
runs confirm such a scenario, with the 00Z HRRR run in particular
showing a surge of convection moving southward through late
afternoon/early evening.  Given potential for locally damaging gusts
in such a scenario, will initially introduce 5%/MRGL risk for wind.

..Goss/Squitieri.. 08/21/2022