MESOSCALE DISCUSSION 1780
   NWS STORM PREDICTION CENTER NORMAN OK
   0835 PM CDT TUE AUG 04 2009
   
   AREAS AFFECTED...PORTIONS MIDDLE-WRN TN...WRN KY...NRN AL...NERN
   MS...SRN MO...NERN AR...EXTREME NERN OK...EXTREME SERN KS.
   
   CONCERNING...SEVERE THUNDERSTORM WATCH 658...659...661...
   
   VALID 050135Z - 050300Z
   
   CORRECTED FOR GEOGRAPHIC HEADER
   
   THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH
   658...659...661...CONTINUES.
   
   CONCERN FOR ORGANIZED SVR POTENTIAL CONTINUES WITH MCS MOVING SEWD
   35-40 KT FROM WRN KY INTO PORTIONS WRN/MIDDLE TN.  COUNTIES IN
   POTENTIALLY AFFECTED PORTIONS WW 659 MAY BE EXTENDED BEYOND
   SCHEDULED 02Z EXPIRATION.
   
   SEVERAL REPORTS OF DAMAGING GUSTS HAVE BEEN RECEIVED DURING PAST 1-2
   HOURS INVOF TN/KY BORDER...ALTHOUGH MEASURED WINDS HAVE BEEN
   SUBSEVERE AT SFC OBS SITES SUCH AS HOP AND CKV.  APEX OF THIS SYSTEM
   WILL MOVE SEWD TOWARD BNA AREA AND ACROSS WRN/SRN PORTIONS MIDDLE TN
   WITH POTENTIAL FOR OCCASIONAL DAMAGING GUSTS.  OUTFLOW BOUNDARY FROM
   EARLIER/EASTERN MCS IS EVIDENT AT 01Z FROM NEAR CHA NWWD CROSS
   WILLIAMSON COUNTY TO ERN DICKSON COUNTY TN.  00Z BNA RAOB MEASURED
   ABOUT 2 KFT DEPTH OF STABLE LAYER ASSOCIATED WITH COLD POOL...AND
   EFFECTIVE LIFTED PARCELS WERE ROOTED ABOUT 1/2 KM AGL.  OLDER
   OUTFLOW BOUNDARY IS MOVING SWWD 10-15 KT ACROSS THIS REGION AND
   AHEAD OF MCS.  RELATED COLD POOL SHOULD BECOME SHALLOWER WITH
   WESTWARD EXTENT AND WITH TIME...INCREASING POTENTIAL FOR DAMAGING
   GUSTS FROM IMPENDING MCS TO REACH SFC W AND SW OF BNA VERSUS FARTHER
   E AND NE.  MLCAPE WILL DIMINISH WITH SWD EXTENT ACROSS NRN AL AND
   NERN MS BECAUSE OF COMBINATION OF SFC DIABATIC COOLING...SOMEWHAT
   WEAKER LAPSE RATES ALOFT...AND DRY AIR JUST ABOVE SFC. 
   HOWEVER...THAT DRYING LAYER ALSO MAY FOSTER ENHANCED DCAPE AND
   DOWNDRAFT ACCELERATION FOR AS LONG AS MCS MAY PERSIST.  THESE AREAS
   WILL BE MONITORED FOR POSSIBLE WW AS CONVECTIVE TRENDS WARRANT.
   
   FARTHER NW...CLUSTER OF STG-SVR TSTMS OVER SERN MO REMAINS IN POCKET
   OF FAVORABLY MOIST/UNSTABLE AIR ALONG AND E OF OUTFLOW BOUNDARY FROM
   KY/TN COMPLEX.  THIS ACTIVITY LIKEWISE MAY ORGANIZE INTO MCS AND
   MOVE SEWD TOWARD PORTIONS WRN TN AND WRN KY.  WIND DAMAGE POTENTIAL
   SHOULD DECREASE WITH EWD EXTENT OVER PROGRESSIVELY DEEPER COLD POOL
   FROM EARLIER CONVECTION...WITH LARGE HAIL POSSIBLE ON BOTH SIDES OF
   OUTFLOW BOUNDARY.  PORTIONS NERN AR AND MO BOOT-HEEL WILL BE
   MONITORED FOR POSSIBLE WW...EITHER ANEW OR AS EXTENSION OF WW
   658....BEFORE SCHEDULED 03Z EXPIRATION OF WW 658.  POTENTIAL FOR SVR
   APPEARS TO BE DIMINISHING WITH TIME...BUT NOT ENTIRELY GONE
   YET...ACROSS WRN OZARKS.  SGF RAOB INDICATED FAVORABLE
   MOISTURE...INSTABILITY AND DEEP-LAYER SHEAR...BUT FRONTAL LIFT MAY
   NOT BE SUFFICIENT TO OVERCOME CINH NOW THAT DIABATIC COOLING HAS
   BEGUN IN BOUNDARY LAYER AND HEIGHTS ALOFT ARE RISING.
   
   ..EDWARDS.. 08/05/2009
   
   
   ATTN...WFO...MRX...LMK...OHX...HUN...PAH...MEG...LSX...LZK...
   SGF...TSA...
   
   LAT...LON   37739093 37618947 37108802 37178733 37348664 36278555
               35008566 34538621 34338726 34458841 34968973 36499093
               36459459 36829512 37169461 37669117 37739093