Mesoscale Discussion 0408
   NWS Storm Prediction Center Norman OK
   0327 PM CDT Fri Apr 23 2021

   Areas affected...parts of western north-central TX and far
   southwestern OK

   Concerning...Tornado Watch 100...

   Valid 232027Z - 232230Z

   The severe weather threat for Tornado Watch 100 continues.

   SUMMARY...A mesoscale area most favorable for a tornadic supercell
   will be near the adjacent portions of southwest OK/northwest TX
   during the 5-7 pm period.  Large to giant hail is possible.

   DISCUSSION...Latest subjective surface mesoanalysis places a moist
   axis east of the dryline and extending from near Seymour and
   protruding north-northwest to near Childress, with lower 60s degree
   F dewpoints near and south of the OK border as of 325 pm.  RAP
   forecast soundings show continued differential thermal advection
   occurring during the next few hours with 500 mb temperatures cooling
   from -16 deg C to -18 across this region.  Additional heating and
   low-level moistening will contribute to a very unstable airmass
   within this confined mesoscale corridor (2500-3000 J/kg MLCAPE). 
   Some low-level backing of surface winds is expected which will
   contribute to enlarging the hodograph during the 5-7 pm period.  If
   an established quasi-discrete supercell manages to develop
   (increasingly probable at this point), a tornado risk may accompany
   it for an hour or so.  Large to giant hail (1 to 3.5 inches in
   diameter) may also occur with the discrete surface-based updrafts. 
   Further storm development and consolidation of cold pools into a
   cluster by early evening will likely diminish the supercell-tornado
   risk towards sunset.

   ..Smith.. 04/23/2021

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...OUN...LUB...AMA...

   LAT...LON   33569969 34179994 34450025 34759999 34459925 34049879
               33699885 33459921 33569969