MESOSCALE DISCUSSION 1401
   NWS STORM PREDICTION CENTER NORMAN OK
   0230 PM CDT SUN JUN 26 2011
   
   AREAS AFFECTED...PORTIONS CENTRAL/SRN SD...CENTRAL/NRN NEB...NEB
   PANHANDLE...SERN WY.
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 557...
   
   VALID 261930Z - 262130Z
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 557
   CONTINUES.
   
   NWRN NEB CONVECTION HAS EVOLVED INTO SVR AND EXPANDING MCS WITH TWO
   EMBEDDED HEAVY-PRECIP SUPERCELLS...BASED ON WSR-88D PRODUCTS FROM
   SRN SANDHILLS UNIT.  DOMINANT MESOCIRCULATION MAY EMERGE FROM ONE OR
   BOTH RELATED STORM-SCALE VORTICES...SUPPORTING POTENTIAL FOR
   DEVELOPMENT OF BOW ECHO AND ACCELERATION OF COMPLEX ESEWD ACROSS NRN
   NEB...AND IN TURN...ENHANCED DAMAGING WIND THREAT.  MEANWHILE...THIS
   ACTIVITY SHOULD CONTINUE ACROSS SANDHILLS WITH POTENTIAL FOR
   LARGE/DAMAGING HAIL AND SVR GUSTS...AND A TORNADO OR TWO POSSIBLE AS
   WELL.  VWP AND RUC SOUNDINGS INDICATE FAVORABLE DEEP-LAYER SHEAR AND
   STORM-RELATIVE INFLOW FOR SEVERAL MORE HOURS...WITH MOIST
   ADVECTION/TRANSPORT INTO PROSPECTIVE INFLOW REGION LIKELY. 
   CURRENTLY...MLCINH DOES STRENGTHEN CONSIDERABLY WITH SEWD
   EXTENT...BUT ALSO APPEARS TO BE ERODING NEARLY APACE WITH
   TRANSLATION VECTOR OF MCS.  IF PRESENT TRENDS CONTINUE OR
   ACCELERATE...NEW WW MAY BE NEEDED FOR PORTIONS CENTRAL/NERN NEB
   BEFORE 22Z.
   
   FARTHER NW...DESPITE NWLY/POSTFRONTAL WINDS IN LOWEST LEVELS AND
   RESULTANT DISPLACEMENT OF HODOGRAPH E AND SE OF ORIGIN...18Z UNR
   RAOB SHOWED FAVORABLE BUOYANCY/SHEAR FOR SFC-BASED SUPERCELLS.  RAOB
   REVEALED 0-1 KM AGL SRH 150-200 J/KG DEPENDING ON STORM MOTION
   USED...AND EFFECTIVE SHEAR MAGNITUDE 50-55 KT.  THEREFORE...WRN
   PORTIONS WW SHOULD BE MAINTAINED UNTIL AIR MASS BECOMES TOO STABLE
   TO SUPPORT SVR THREAT WITH EXISTING OR LATER DEVELOPMENT MOVING OUT
   OF BLACK HILLS/BADLANDS REGION.  ONE UNCERTAINTY IS IN DURATION OF
   THIS ACTIVITY...WHICH MAY ENCOUNTER OUTFLOW AIR ADVECTED NWD/NWWD
   FROM NEB MCS.
   
   ADDITIONAL DEVELOPMENT ALSO MAY OCCUR OVER HIGHER TERRAIN OF SERN WY
   OR WRN/SRN PANHANDLE WHERE CINH IS DIMINISHING AND MOISTURE IS
   FAVORABLE...THEN MOVE TOWARD SWRN PORTIONS WW.  TO COVER SPATIAL
   GAP...ADDITIONAL WW ACCORDINGLY MAY BE REQUIRED THIS AFTERNOON W OR
   SW OF WW 557.
   
   ..EDWARDS.. 06/26/2011
   
   
   ATTN...WFO...FSD...OAX...ABR...GID...LBF...UNR...CYS...
   
   LAT...LON   41120360 41410459 42250469 43640324 44720125 44499885
               42969814 42879738 42089746 41399856 41640066 41690187
               41230268 41300261 41120360