MESOSCALE DISCUSSION 0858
   NWS STORM PREDICTION CENTER NORMAN OK
   0208 PM CDT TUE MAY 22 2007
   
   AREAS AFFECTED...CNTRL/ERN SD AND NCNTRL NEB
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 221908Z - 222115Z
   
   18Z MESOANALYSIS PLACES A 997 MB SFC LOW OVER CNTRL ND WITH A
   TRAILING PRE-FRONTAL TROUGH SWD THROUGH ERN SD AND CNTRL NEB. 
   PRIMARY SFC COLD FRONT WAS LOCATED ACROSS NCNTRL-SWRN SD.  
   
   18Z LBF SOUNDING SAMPLED A SUBSIDENCE INVERSION IN WAKE OF THE
   DEPARTING MCV MOVING NEWD THROUGH SERN ND.  BUT...SFC TEMPERATURES
   WERE WARMING RAPIDLY WHERE CLOUDS HAVE THINNED OVER CNTRL/ERN SD
   WITH INHIBITION GRADUALLY WEAKENING.  LOW-LEVEL STREAMLINE ANALYSIS
   SHOWS THE FLOW GRADUALLY BACKING TO SLY ACROSS MOST OF CNTRL/ERN
   PARTS OF NEB/SD AND INCREASING CONVERGENCE WAS CONTRIBUTING TO TSTM
   DEVELOPMENT NEAR/W OF WINNER SD.
   
   INSPECTION OF VWP/PROFILERS SUGGESTS THAT DEEP SLY FLOW EXISTS AS
   THE MID-LEVEL FLOW CONTINUES TO BACK IN ADVANCE OF THE UPSTREAM UPR
   LEVEL TROUGH.  THUS...THERE WILL BE A TENDENCY FOR TSTMS TO BECOME
   LINEAR QUICKLY AS DEEP LAYER FLOW REMAINS ORIENTED PARALLEL TO THE
   BOUNDARY.  LAPSE RATES IN THE H7-H5 LAYER REMAIN QUITE STEEP...ON
   THE ORDER OF 7.5-8 DEG C PER KM...SO DESPITE ONLY MODEST SHEAR IN
   THE LOWEST 6KM...LARGE HAIL WILL BE LIKELY WITH THE STRONGER STORMS.
   
   ACTIVITY SHOULD MOVE SLOWLY NNEWD FROM NCNTRL NEB/SCNTRL SD INTO
   PARTS OF CNTRL-NERN SD LATER THIS AFTN.  TRAINING STORMS WILL ALSO
   HAVE THE RISK OF PROLONGED HEAVY RAINFALL.
   
   ..RACY.. 05/22/2007
   
   
   ATTN...WFO...FSD...ABR...LBF...UNR...
   
   45729899 44509795 43309836 42439958 42120060 42180175
   43370180 44240141 44730125 45729985