Mesoscale Discussion 1953
   NWS Storm Prediction Center Norman OK
   1131 PM CDT Tue Sep 10 2019

   Areas affected...Parts of southeastern South Dakota...southwestern
   Minnesota...northeastern Nebraska...northwestern Iowa

   Concerning...Severe Thunderstorm Watch 643...

   Valid 110431Z - 110600Z

   The severe weather threat for Severe Thunderstorm Watch 643
   continues.

   SUMMARY...An evolving cluster of storms may continue to pose a risk
   for strong surface gusts east of Sioux Falls SD, near the western
   Minnesota/Iowa border area through 1-2 AM CDT.  It is not certain
   that a new severe weather watch will be needed farther east, but
   trends will continue to be monitored for this possibility.

   DISCUSSION...Vigorous thunderstorm development persists, southeast
   and south of a lower/mid tropospheric cyclonic vorticity center
   which has become increasingly evident in radar imagery, currently
   east of Mitchell SD.  This is also near the nose of a strengthening
   and gradually veering southerly low-level jet (40-50 kt at 850 mb),
   but generally to the cool side of the effective warm frontal zone
   (across southeastern South Dakota) and a southeastward advancing
   outflow boundary (across north central Nebraska).  

   Low-level shear is strong ahead of the convective outflow across
   southeastern South Dakota, where modest near surface easterlies veer
   to southerly and southwesterly aloft.  However, north of the surface
   front, near surface thermodynamic profiles are cool and stable to
   surface-based convection.  The risk for tornadoes appears low, but
   the environment may be conducive to strong surface gusts as activity
   spreads east of the Sioux Falls area, near the western
   Minnesota/Iowa border area through 06-07Z.

   This leading convection has been advancing eastward roughly with the
   modest 20-30 kt westerly deep-layer ambient mean flow, but some
   eastward acceleration is possible during the next couple of hours.

   ..Kerr.. 09/11/2019

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

   ATTN...WFO...MPX...DMX...FSD...OAX...

   LAT...LON   44089630 44149577 44019490 43469464 42879561 42609687
               42569745 42949775 43469742 43799736 44089630