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Mesoscale Discussion 218
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   Mesoscale Discussion 0218
   NWS Storm Prediction Center Norman OK
   0146 PM CST Tue Feb 28 2017

   Areas affected...south central through northern AR...southern
   MO...southern IL through far west KY

   Concerning...Severe potential...Tornado Watch likely 

   Valid 281946Z - 282215Z

   Probability of Watch Issuance...80 percent

   SUMMARY...Thunderstorms are expected to develop this afternoon from
   south central through northern AR into southern MO and subsequently
   expand east into southern IL and far west KY. Tornadoes, a few of
   which could be strong, very large hail and damaging wind may
   accompany some of the storms. A tornado watch will likely be needed
   for a portion of this region before 22Z.

   DISCUSSION...As of early this afternoon the pre-frontal warm sector
   continues to destabilize over the lower to mid MS Valley. Low to mid
   60s F dewpoints will advect northward through the evening beneath
   plume of eastward-expanding steep mid-level lapse rates. RAP
   objective analysis currently indicates a corridor of 1000-1500 J/kg
   MLCAPE from MO through AR and eastern OK. A capping inversion at the
   base of the elevated-mixed layer, widespread middle to high clouds,
   and weak forcing for ascent have inhibited thunderstorm development
   so far. However, numerous breaks in the high clouds have evolved,
   and shallow cumulus development is evident across AR. WV imagery and
   RUC analysis implies a mid-level impulse moving through OK
   downstream from the primary shortwave trough located over the
   southern high plains. Thus a gradual increase in deeper forcing for
   ascent and differential heating in the boundary layer should
   eventually contribute to surface-based thunderstorm development in
   this region, and most CAM guidance indicate thunderstorm initiation
   by late afternoon. A southwesterly low-level jet will undergo a
   substantial increase during the evening with enlarged 0-1 km
   hodographs and strong effective bulk shear supporting fast moving
   supercells with low-level mesocyclones.

   ..Dial/Hart.. 02/28/2017


   LAT...LON   34209185 34649401 36709447 37899331 38769035 38478887
               37168859 35349027 34209185 

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