Mesoscale Discussion 1427
   NWS Storm Prediction Center Norman OK
   0909 PM CDT Fri Aug 06 2021

   Areas affected...Parts of southern South Dakota and adjacent
   northern Nebraska

   Concerning...Severe Thunderstorm Watch 410...

   Valid 070209Z - 070415Z

   The severe weather threat for Severe Thunderstorm Watch 410
   continues.

   SUMMARY...Rapidly intensifying thunderstorm activity with increasing
   organization and the potential to produce severe wind gusts appears
   possible through 11 PM-1 AM CDT.  Trends are being monitored for the
   possibility of an additional severe weather watch east of WW 410.

   DISCUSSION...Convection appears to have generated a fairly
   significant surface cold pool, with 4-6 mb 2 hourly pressure rises
   evident in 01Z surface observations at Rapid City, SD and Chadron,
   NE.  As this cold pool advances eastward along the remnant zone of
   stronger daytime differential surface heating/boundary-layer mixing,
   thunderstorm activity continues to increase and intensify along its
   leading edge.  This includes areas as far north as the Interstate 90
   corridor, west of Philip, SD, but strongest storm development may be
   maintained near the southern flank of the cold pool, near the South
   Dakota/Nebraska border vicinity.  This is roughly along the
   northeastern edge of the warmer and more strongly capping elevated
   mixed-layer air, which extends eastward into the Sioux Falls/Sioux
   City area of the mid Missouri Valley.

   During the past few hours, surface dew points have increased from
   60-65F at Valentine, NE, where temperatures remain in the upper 80s
   F.  This has been aided by advection on easterly near surface flow,
   with dew points as high as the lower/mid 70s at Yankton, SD and
   Sioux City, IA, where the nose of a nocturnally strengthening
   southerly low-level jet (30-40 kt at 850) is forecast to become
   focused by 06Z.

   As eastward advancing convection encounters increasingly moist
   inflow characterized by large CAPE in excess of 3000 J/kg, there
   appears potential for substantive intensification and upscale
   growth.  With easterly low-level flow contributing to strong
   deep-layer shear on the order of 40-50 kt, if this occurs, activity
   likely will become increasingly organized with the risk for severe
   wind gusts increasing once again, aided by steep lower/mid
   tropospheric lapse rates.

   ..Kerr.. 08/07/2021

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

   ATTN...WFO...FSD...OAX...ABR...LBF...UNR...

   LAT...LON   44000070 44259959 44309759 44119690 43549667 42549711
               42669814 42789904 42790012 42930051 43490083 44000070