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Mesoscale Discussion 756
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   Mesoscale Discussion 0756
   NWS Storm Prediction Center Norman OK
   1259 PM CDT Thu May 18 2017

   Areas affected...Portions of western/central Oklahoma

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

   Valid 181759Z - 182000Z

   Probability of Watch Issuance...95 percent

   SUMMARY...Severe thunderstorms will develop across portions of
   western Oklahoma this afternoon. Tornadoes, a few of which may be
   strong, very large hail, and damaging winds will be possible. A PDS
   (Particularly Dangerous Situation) tornado watch will be issued
   within the next hour.

   DISCUSSION...As mid-level forcing for ascent gradually increases
   this afternoon, thunderstorms will increase in coverage across much
   of the region over the next 1-3 hours. Surface observations indicate
   dew points have risen into the mid/upper 60s over much of the
   discussion area. Wave/billow structures on visible satellite suggest
   convective inhibition remains over parts of Oklahoma and Kansas this
   afternoon, but continued boundary-layer heating/moistening and
   cooling aloft are forecast to remove any remaining inhibition. In
   turn, as the dry line focuses near the Oklahoma/Texas border,
   thunderstorms will develop and likely become severe quite quickly.
   Moreover, open warm sector development is also possible across
   portions of southwest Oklahoma, within zones of confluence and
   differential heating.

   With the presence of moderate/strong buoyancy (around 2500-3500 J/kg
   of MLCAPE) and effective shear upwards of 45-50 kt, initial
   supercellular modes appear probable. Some forecast soundings
   indicate a deep-layer wind profile marginally supportive of a few
   left splits with initial warm sector development east of the dry
   line this afternoon. Cell mergers/interference would preclude a
   higher-end severe threat. However, as low-level hodographs enlargen
   (with greater clockwise looping) late this afternoon into this
   evening, cyclonically rotating supercells may become favored, with a
   greater eastward component of movement. Any such discrete cell would
   possess a threat for tornadoes (which could be strong), very large
   hail, and damaging winds.

   Farther west along the dry line, severe thunderstorms will likely
   organize near the Oklahoma/Texas Panhandle border. Some potential
   exists for northward-moving cells (from initial convection to the
   south) to interfere with these cells, as well as cause convective
   overturning, which would limit the severe threat some. However, the
   genesis region of the southern cells, as well as their expected
   motion, will likely keep them east of cells generating along the dry
   line. In turn, a relatively pristine air mass should exist for
   supercellular development by mid/late afternoon. Backed surface flow
   and increasing boundary-layer moisture ahead of the dry line will
   favor a threat of tornadoes, a few of which could be strong. Very
   large hail and damaging winds will also be possible. A PDS
   (Particularly Dangerous Situation) tornado watch will be issued
   within the next hour.

   ..Picca/Goss.. 05/18/2017

   ...Please see for graphic product...


   LAT...LON   33969918 33989970 34060033 34320042 35590020 36170014
               36939980 36959850 36969817 36059799 34739797 34209802
               33969851 33969918 

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