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Mesoscale Discussion 797
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   Mesoscale Discussion 0797
   NWS Storm Prediction Center Norman OK
   0145 AM CDT Sat May 20 2017

   Areas affected...Southeast Missouri...northeast Arkansas...southern

   Concerning...Severe potential...Watch likely 

   Valid 200645Z - 200815Z

   Probability of Watch Issuance...80 percent

   SUMMARY...A threat of damaging wind, a brief tornado and marginal
   hail is expected to develop eastward toward the Mississippi and
   lower Ohio Valleys tonight.

   DISCUSSION...The leading edge of a line of storms driven by outflow
   continues to move eastward across southern MO and northwest AR, and
   extending into southeast OK. Meanwhile, other cells were
   periodically developing ahead of the line, with the strongest
   activity containing hail over southeast MO currently. Additional
   cells also extend eastward along the OH river along and north of a
   stationary front.

   The air mass remains very moist and unstable, with sufficient
   effective shear and mean flow to sustain long lived storms. While
   the current linear MCS is not optimal for tornadoes, a brief tornado
   cannot be ruled out across the warm sector as the upper trough
   continues to emerge and the low-level jet increases further. The
   best low-level shear should remain near the stationary/warm front,
   from southeast MO into southern IL. Also in this area, deep-layer
   shear vector orientation appears more favorable for individual cells
   even within the approaching line.

   ..Jewell/Guyer.. 05/20/2017

   ...Please see for graphic product...


   LAT...LON   38468798 37738836 36878906 35948974 35519056 35329142
               35449197 35749232 36199224 37219128 37919034 38338958
               38538903 38588829 38468798 

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