MESOSCALE DISCUSSION 2166
   NWS STORM PREDICTION CENTER NORMAN OK
   0203 AM CDT FRI OCT 30 2009
   
   AREAS AFFECTED...NERN LA/ERN AR/WRN MS INTO WRN TN
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 300703Z - 300800Z
   
   PERIODIC INCREASES IN TSTM ACTIVITY ARE POSSIBLE OVERNIGHT INTO THE
   EARLY MORNING ACROSS NERN LA TO WRN TN...WITH AN ISOLATED THREAT FOR
   STRONG WIND GUSTS AND/OR A BRIEF TORNADO.  GIVEN WEAK
   INSTABILITY...OVERALL SEVERE WEATHER THREAT DOES NOT WARRANT A WATCH
   AT THIS TIME...BUT TRENDS WILL CONTINUE TO BE MONITORED.
   
   REGIONAL RADARS SHOWED CORRIDOR OF SHOWERS WITH EMBEDDED TSTMS
   EXTENDING FROM E TX/WRN-NRN LA INTO SERN MO/WRN IL.  RADAR AND
   LIGHTNING DATA INDICATED THE STRONGEST TSTMS WERE LOCATED ALONG THE
   LEADING EDGE OF THIS EXTENSIVE AREA OF ACTIVITY...WITH SOME STORM
   ORGANIZATION OVER NERN LA/SERN AR AND ALSO ACROSS FAR ERN AR.  THESE
   STORMS AREA LOCATED AHEAD OF A COLD FRONT ADVANCING EWD INTO THE
   LOWER MS VALLEY OVERNIGHT AND ARE LIKELY UNDER THE INFLUENCE OF A
   ZONE OF LOW LEVEL CONVERGENCE...GIVEN 850 MB SSWLY WINDS OVER SE TX
   TO AR AND AT THE SAME LEVEL...SSELY WINDS OVER MS TO SERN LA.
   
   THUS...GIVEN THE PRESENCE OF A VERY MOIST AIR MASS /SURFACE
   DEWPOINTS 70+ F/ EXTENDING INTO THE MID-SOUTH...LOW LEVEL
   CONVERGENCE BENEATH WEAK HEIGHT FALLS SPREADING EWD AHEAD OF PLAINS
   UPPER TROUGH WILL SUPPORT ADDITIONAL TSTMS INTO THE EARLY MORNING. 
   STRONG SSWLY MID LEVEL WINDS COMBINED WITH THE AFOREMENTIONED LOW
   LEVEL FLOW WILL MAINTAIN EFFECTIVE BULK SHEAR 40-50 KT.  ALTHOUGH
   INSTABILITY IS WEAK...THE STRONG DEEP LAYER SHEAR WILL SUPPORT
   PERIODIC STORMS/CLUSTERS TO BECOME ORGANIZED WITH AN ISOLATED THREAT
   FOR MAINLY STRONGER WIND GUSTS...GIVEN 40-50 KT WINDS JUST OFF THE
   SURFACE IN THE LOWER MS VALLEY.  OBJECTIVE ANALYSIS AND AREA WSR-88D
   VWPS INDICATED VERY STRONG LOW LEVEL SHEAR ACROSS THE LOWER MS
   VALLEY WITH SFC-1 KM VALUES EXCEEDING 40 KT AND EFFECTIVE SRH
   RANGING FROM 300-600 M2/S2.  THIS LOW LEVEL SHEAR COMBINED WITH THE
   LACK OF SURFACE BASED INHIBITION WITHIN A VERY MOIST BOUNDARY LAYER
   IS SUPPORTIVE OF A TORNADO THREAT...THOUGH ISOLATED DUE TO THE
   OVERALL WEAK INSTABILITY.
   
   ..PETERS.. 10/30/2009
   
   
   ATTN...WFO...PAH...MEG...JAN...LZK...SHV...
   
   LAT...LON   31899233 33089183 34429095 35299061 36578984 36528895
               35928872 33818950 32069039 31449124 31559212 31899233