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...

   ...SUMMARY...
   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,
   propagating south/southwestward.

   ...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.

   ..Jewell/Moore.. 09/17/2021

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