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Mesoscale Discussion 1677
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   Mesoscale Discussion 1677
   NWS Storm Prediction Center Norman OK
   0106 AM CDT Sun Sep 06 2020

   Areas affected...Southern MN...Northern/Northeastern IA

   Concerning...Severe Thunderstorm Watch 486...

   Valid 060606Z - 060730Z

   The severe weather threat for Severe Thunderstorm Watch 486
   continues.

   SUMMARY...Threat for large hail continues across southern MN and
   northern/northeast IA. Potential for damaging wind gusts has also
   increased across the region.

   DISCUSSION...Recent surface analysis places a warm front from BKX
   (in far east-central SD) southwestward across southwest MN and
   north-central IA to near CID in southeast IA. A strong low-level jet
   (i.e. 40 to 50 kt) continues across this tight frontal zone,
   contributing to strong warm-air advection and widespread elevated
   thunderstorms.  

   Recent RAP soundings reveal a mid-level dry layer, roughly between
   850 and 700 mb, from a remnant elevated mixed layer. This EML is
   contributing to both strong buoyancy as well as the potential for
   strong downbursts. Regional radar imagery shows that a few of these
   storms have begun to accelerate more southward/southeastward,
   indicative of strong outflow and a tendency toward more forward
   propagation. A 54 kt was measured at RWF at 0516Z and other strong
   gusts of 42 kt and 38 kt were measured at MKT and AUM, respectively.
   This is evidence that despite the elevated character of the storms,
   the downbursts are strong enough to penetrate through the low-level
   stability and reach the surface. Consequently, the threat for
   damaging wind gusts has increased. The threat for large hail also
   remains over the region.

   ..Mosier.. 09/06/2020

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

   ATTN...WFO...DVN...ARX...MPX...DMX...FSD...

   LAT...LON   44729636 45059549 44899454 44199263 43329128 42029120
               41589159 41779270 43539594 44729636 

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Page last modified: September 06, 2020
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