MESOSCALE DISCUSSION 0677
   NWS STORM PREDICTION CENTER NORMAN OK
   0254 PM CDT SUN MAY 22 2016

   AREAS AFFECTED...PORTIONS OF CNTRL/WRN NEB...S-CNTRL SD

   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 

   VALID 221954Z - 222130Z

   PROBABILITY OF WATCH ISSUANCE...80 PERCENT

   SUMMARY...ISOLATED TO WIDELY-SCATTERED THUNDERSTORM DEVELOPMENT IS
   EXPECTED LATER THIS AFTERNOON. SUPERCELLS CAPABLE OF LARGE
   HAIL...DAMAGING WIND...AND A COUPLE OF TORNADOES WILL BE POSSIBLE.
   WATCH ISSUANCE WILL LIKELY BE REQUIRED BY 21Z.

   DISCUSSION...AT 1930Z...SLOWLY DEEPENING CU WAS NOTED ALONG A WEAK
   SFC BOUNDARY DRAPED FROM WRN NEB INTO S-CNTRL SD...WITH CG ACTIVITY
   RECENTLY NOTED ACROSS CHERRY COUNTY. SOME CU WAS ALSO NOTED ALONG A
   DRYLINE NEAR THE NE/CO/KS BORDERS. THE THERMODYNAMIC ENVIRONMENT
   ACROSS THIS AREA...AS SAMPLED BY THE 18Z LBF SOUNDING...IS
   CHARACTERIZED BY STEEP MIDLEVEL LAPSE RATES AND MODERATE BUOYANCY.
   THE MODIFIED LBF SOUNDING YIELDS MLCAPE OF AROUND 2000 J/KG...WHICH
   IS IN AGREEMENT WITH RECENT MESOANALYSIS ESTIMATES. THE OBSERVED
   WIND PROFILE FROM THE SOUNDING AND LNX VWP INDICATES FAVORABLE
   EFFECTIVE HELICITY OF AROUND 150-200 M2/S2...THOUGH DEEP-LAYER SHEAR
   IS RELATIVELY WEAK AND SOME UNFAVORABLE BACKING OF THE MIDLEVEL FLOW
   WAS NOTED AS WELL. 

   IT APPEARS THAT A WEAK VORT MAX IS APPROACHING SW NEB...BUT IT IS
   UNCLEAR IF THIS FEATURE WILL BE SUFFICIENT TO INITIATE AND SUSTAIN
   DEEP CONVECTION...GIVEN SOME RESIDUAL CAPPING AND VERY DRY AIR ALOFT
   NOTED ON THE LBF SOUNDING. LATE THIS AFTERNOON...ASCENT WILL BEGIN
   TO INCREASE AHEAD OF A STRONGER UPPER TROUGH CURRENTLY MOVING EWD
   OUT OF THE GREAT BASIN...WITH INCREASING CONVECTIVE COVERAGE
   EXPECTED IN THE 22-00Z TIME FRAME.

   ONCE INITIATION OCCURS...SUPERCELLS CAPABLE OF LARGE HAIL AND
   DAMAGING WINDS WILL BE POSSIBLE. SOME TORNADO RISK WILL ALSO
   EXIST...ESPECIALLY ACROSS THE SRN PART OF THE MCD AREA...WHERE
   LOW-LEVEL WINDS WILL BE A LITTLE MORE BACKED IN RESPONSE TO
   DEEPENING LOW PRESSURE OVER ERN CO. STORM MODE MAY BECOME
   INCREASINGLY MIXED WITH NWD EXTENT GIVEN THE PRESENCE OF BACKED
   MIDLEVEL FLOW...BUT INSTABILITY/SHEAR WILL STILL BE SUFFICIENT FOR A
   SEVERE RISK EXTENDING INTO CNTRL SD.

   ..DEAN/HART.. 05/22/2016


   ATTN...WFO...FSD...ABR...GID...LBF...UNR...GLD...

   LAT...LON   40900196 41460220 42940143 44630092 44400026 44129963
               43419919 42399948 40040028 40010196 40900196