SPC AC 170535
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1235 AM CDT Fri Sep 17 2021
Valid 171200Z - 181200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
Severe thunderstorms appear unlikely across the contiguous United
States today. However, a few strong storms are possible across parts
of west Texas, and southern Arizona during the late afternoon.
...Great Lakes into the central Plains and into west TX...
A fast-moving and deep upper trough will move from the northern
Plains/Upper MS Valley across the Great Lakes through 00Z, lifting
east/northeast into Quebec overnight. At the surface, a cold front
will extend roughly from Lake Michigan into central KS and the TX
Panhandle by 21Z, with 60s F dewpoints ahead of it.
The strongest lift the upper trough will quickly depart the Upper
MI/Lake Superior region, leaving behind weakening convergence along
the boundary. Still, heating and sufficient moisture, as well as
residual cool air aloft will likely yield regenerating storms along
the front, from IL/WI southwestward into KS and western OK. Shear
will be weak in these areas, with only short-lived updrafts likely.
Other storms are expected to form during the peak heating hours from
the TX Panhandle into the South Plains. Here, lapse rates will be
steep below 500 mb, and could result in locally strong wind gusts.
Most CAMs show storms initiating across the eastern TX Panhandle,
...Far southern AZ...
Gulf moisture will begin to return to the border region of southern
Arizona, possibly contributing to 500-1000 J/kg MLCAPE by late
afternoon. Heating will result in inverted-V profiles, and a few
storms may develop in this regime by late afternoon or early
evening. Isolated, strong convective gusts cannot be ruled out, but
being diurnally driven in a weak shear environment, any severe wind
risk appears limited in magnitude, space and time.
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