Mesoscale Discussion 1903
   NWS Storm Prediction Center Norman OK
   0515 PM CDT Fri Aug 30 2019

   Areas affected...Portions of eastern MO into southwestern IL

   Concerning...Severe Thunderstorm Watch 629...

   Valid 302215Z - 302345Z

   The severe weather threat for Severe Thunderstorm Watch 629
   continues.

   SUMMARY...Isolated severe threat, including the potential for a
   brief tornado or two, should continue near and south of the St.
   Louis metro through the early evening.

   DISCUSSION...A supercell that formed earlier this afternoon along a
   surface boundary across eastern MO produced large hail up to 2.5
   inches in diameter. This storm has also shown occasional low-level
   rotation as it approached the St. Louis metro area over the past
   hour or so. Although low-level flow across this region is not overly
   strong, it does veer substantially from northeasterly along and just
   north of the surface boundary to south-southwesterly at mid levels
   per recent VWPs from KLSX. This veering is contributing to around
   40-50 kt of effective bulk shear, which will continue to support
   organized thunderstorms, including supercells, in the short term.
   Around 100-150 m2/s2 of effective SRH should also promote some
   potential for low-level rotation within any supercell that can
   maintain itself along/near the surface boundary through the early
   evening. A isolated, brief tornado remains possible, along with a
   large hail and damaging straight-line wind threat. This isolated
   severe risk will likely diminish later this evening (generally after
   01Z) as the loss of diurnal heating results in a gradually
   stabilizing boundary layer and diminishing instability.

   ..Gleason.. 08/30/2019

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

   ATTN...WFO...LSX...

   LAT...LON   38219113 38619078 38809034 38978947 38748929 38328930
               38188974 37789024 37349063 37339115 38219113