SPC AC 231629

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 AM CDT Sat May 23 2020

   Valid 231630Z - 241200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   OVER PORTIONS OF NORTHERN ILLINOIS AND EASTERN IOWA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF THE
   PLAINS STATES....

   ...SUMMARY...
   Scattered severe thunderstorms, some with tornadoes, will cross
   parts of eastern Iowa, northern Illinois and southern Wisconsin from
   midday through this afternoon.  Thunderstorms with very large hail
   and severe wind will affect parts of the northern and southern Great
   Plains.

   ...Northern IL and Vicinity...
   An upper low is rotating eastward across IA this morning.  The
   latest surface analysis has a low near Des Moines, with the a cold
   front extending southward into northern MO.  Southeasterly low-level
   winds to the east of the low across eastern IA and northern IL are
   enhancing vertical shear and resulting in favorable hodograph
   structures for rotating storms later today.  Visible satellite
   imagery shows considerable daytime heating is occurring over much of
   this region, which combined with dewpoints in the 60s will yield
   afternoon MLCAPE values of 1000-1500 J/kg.  All of these parameters
   lend to the potential for active severe weather later today.

   Current indications are that storms will form along/ahead of the
   cold front and spread across the ENH risk area this afternoon. 
   Discrete storm mode appears likely, resulting in multiple
   supercells.  A few tornadoes are expected, along with large hail and
   damaging wind gusts.  Activity should approach the Chicago/Milwaukee
   areas this evening.

   ...TX...
   A strong dryline is expected to form this afternoon across west TX,
   with full daytime heating and dewpoints in the mid 60s expected to
   the east of the boundary.  Current indications are that the cap will
   sufficiently weaken to allow scattered thunderstorms to form by
   mid-late afternoon from the Panhandle southward into the eastern
   Permian Basin.  Low-level winds are not particularly strong, but
   sufficient deep-layer shear and ample CAPE (MLCAPE of 3500+ J/kg)
   will pose a risk of supercells capable of very large hail and
   damaging winds.  This activity will spread into central TX and
   perhaps western OK tonight before weakening.

   ...Northern Plains...
   Water vapor imagery shows an upper trough moving across the northern
   Rockies.  This feature will help to promote thunderstorm development
   over eastern WY into the western Dakotas/NE and northeast CO by
   mid-late afternoon.  Multiple lines and clusters of storms will
   affect this region through the evening, with a risk of large hail
   and damaging winds over a relatively large area.  The evolution of
   the storms tonight is unclear, but the pattern would be favorable
   for one or more bowing complexes maintaining intensity into parts of
   central/eastern NE/SD.

   ..Hart/Bentley.. 05/23/2020

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