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Mesoscale Discussion 866
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   Mesoscale Discussion 0866
   NWS Storm Prediction Center Norman OK
   0204 PM CDT Sat May 27 2017

   Areas affected...Northern and eastern Oklahoma

   Concerning...Severe potential...Watch likely 

   Valid 271904Z - 272030Z

   Probability of Watch Issuance...95 percent

   SUMMARY...A tornado watch probably will be issued by 20-21Z.  Rapid
   supercell development appears likely by around 23-00Z, if not
   before, particularly near the Tulsa area.

   DISCUSSION...The latest objective mesoanalysis suggests that
   inhibition for boundary layer parcels is at least beginning to
   weaken in response to insolation along the surface frontal zone now
   extending across northern Oklahoma.  More substantive weakening of
   inhibition appears likely to await the southward suppression of
   mid-level heights and the northern periphery of the plume of very
   warm elevated mixed layer air, as coupled impulses within the
   mid-latitude and subtropical westerlies continue to emerge from the
   southern Rockies.  The latest Rapid Refresh, among other model
   output, suggests that this may not occur until closer to, or perhaps
   after, 23-00Z.  However, convective initiation seems at least
   possible earlier.

   Regardless, once the cap weakens, thunderstorm development will be
   rapid, in the presence of strong to extreme CAPE (in excess of 4000
   J/kg) and strong deep layer shear.  This probably will at least
   initially include the risk for supercells, with potential for very
   large hail and a couple of tornadoes, particularly on the nose of
   the corridor of strongest pre-frontal surface heating, roughly in
   the vicinity of Tulsa.  Additional, isolated supercell development
   may not be out of the question, farther southwest along the
   Interstate 44 corridor near the Oklahoma City area.

   ..Kerr.. 05/27/2017

   ...Please see for graphic product...


   LAT...LON   35699769 35919864 36339876 36749764 36979633 36899493
               36309478 35849493 35099573 34989694 35509718 35699769 

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