Mesoscale Discussion 0645
   NWS Storm Prediction Center Norman OK
   0321 PM CDT Wed May 20 2020

   Areas affected...Portions of western Texas

   Concerning...Severe potential...Watch likely 

   Valid 202021Z - 202245Z

   Probability of Watch Issuance...95 percent

   SUMMARY...An increase in storm coverage and intensity is expected
   over the next few hours. Storms may pose a severe hail threat early
   on, including the possibility of 2+ inch stones. A tornado also
   cannot be ruled out, especially with storms traversing a baroclinic
   zone. Upscale growth into one or more intense clusters is possible,
   where damaging winds may also become a concern. A WW issuance will
   be needed shortly.

   DISCUSSION...Strong diurnal heating and weakening convective
   inhibition ahead of a dryline has recently encouraged the
   development of a CU field across west TX, where convective
   initiation is underway. Glancing upper-level support from a
   mid-level trough to the northwest, combined with continued boundary
   layer mixing should support increasing convective coverage through
   the evening hours.

   A relatively weak vertical wind field (below 300 mb) across much of
   west TX is in place, with bulk effective shear values remaining
   under 30 knots. As such, mainly multicellular convection is
   expected, with a transient supercell possible. Very steep deep-layer
   lapse rates exceeding 8.5 C/km will support MLCAPE/MUCAPE values
   above 2000/3000 J/kg. Severe hail may accompany the more organized
   cells/clusters, with a couple instances of 2+ inch diameter stones
   possible. In addition, visible satellite and surface METAR
   observations depict a differential heating boundary across southern
   parts of northwest TX. Here, locally higher effective SRH (100+
   m2/s2) is present, based on RAP forecast soundings and Mesoanalysis.
   Any transient supercell structure traversing this boundary may
   acquire brief deep-layer rotation, supporting an enhanced threat for
   significant severe hail, damaging winds, and perhaps a tornado.

   Weak deep-layer shear and ample evaporative cooling in a dry
   sub-cloud layer may allow for efficient cold pool mergers and
   upscale growth into one or more relatively short-lived MCSs, as
   supported by CAM guidance. Damaging gusts may accompany this
   activity.

   ..Squitieri/Guyer.. 05/20/2020

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

   ATTN...WFO...OUN...SJT...LUB...AMA...MAF...

   LAT...LON   31989923 31089989 30890114 32260246 32880259 34670301
               36030273 36190218 35690151 34790056 34029997 32909936
               31989923