MESOSCALE DISCUSSION 0856
   NWS STORM PREDICTION CENTER NORMAN OK
   0940 AM CDT SAT MAY 10 2008
   
   AREAS AFFECTED...PARTS OF SRN AR INTO NRN LA...MS
   
   CONCERNING...SEVERE POTENTIAL...WATCH LIKELY 
   
   VALID 101440Z - 101545Z
   
   A WW MAY BE NEEDED SHORTLY.  IT APPEARS THAT THE RISK FOR TORNADOES
   COULD INCREASE BY EARLY AFTERNOON...IN ADDITION TO AN INCREASING
   RISK FOR LARGE HAIL.
   
   THUNDERSTORMS CONTINUE TO SLOWLY INTENSIFY WITHIN LOWER/MID
   TROPOSPHERIC WARM ADVECTION REGIME ACROSS WESTERN/SOUTHERN ARKANSAS.
   THIS FORCING APPEARS TO BE OCCURRING JUST AHEAD OF A SUBTROPICAL
   IMPULSE ALREADY PROGRESSING INTO THE SOUTHERN PLAINS...IN ADVANCE OF
   MORE PROMINENT INTENSIFYING POLAR IMPULSE DIGGING ACROSS THE CENTRAL
   ROCKIES.  AND...THIS WILL CONTINUE TO SPREAD EASTWARD TOWARD THE
   TENNESSEE VALLEY LATE THIS MORNING INTO THE AFTERNOON HOURS.
   
   WHILE LARGE HAIL MAY BE THE PRIMARY SEVERE THREAT...AT LEAST
   INITIALLY...WITH ACTIVITY DEVELOPING ABOVE A RELATIVELY COOL/STABLE
   BOUNDARY LAYER...THERE IS CONCERN THAT THE BOUNDARY LAYER MAY BEGIN
   A RAPID DESTABILIZATION AS A SURFACE WARM FRONT REDEVELOPS NORTHWARD
   THROUGH THE OZARK PLATEAU.  BOUNDARY CURRENTLY EXTENDS NEAR THE
   LOUISIANA/ARKANSAS BORDER...AND A VEERING OF SURFACE WINDS FROM
   EASTERLY TO SOUTHERLY BY EARLY AFTERNOON WILL ALLOW UPPER 60S TO
   AROUND 70F SURFACE DEW POINTS TO OVERSPREAD REGION.
   
   MIXED BOUNDARY LAYER CAPE INCREASING IN EXCESS OF 2000 J/KG...
   COUPLED WITH INCREASING LOW-LEVEL SHEAR AS SOUTHERLY 850 MB FLOW
   STRENGTHENS TO 30+ KT...MAY SUPPORT AN INCREASING RISK FOR TORNADOES
   WITH SUPERCELLS IN THE PRESENCE OF STRONG DEEP LAYER SHEAR.
   
   ..KERR.. 05/10/2008
   
   
   ATTN...WFO...MEG...JAN...LZK...SHV...
   
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