MESOSCALE DISCUSSION 2108
   NWS STORM PREDICTION CENTER NORMAN OK
   1026 AM CDT THU OCT 18 2007
   
   AREAS AFFECTED...PARTS OF NRN MS/NW AL THRU WRN AND MIDDLE
   TN...WRN/CNTRL KY INTO SRN IND
   
   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 
   
   VALID 181526Z - 181730Z
   
   TRENDS ARE BEING CLOSELY MONITORED FOR AN INCREASING SEVERE THREAT
   AND THE POSSIBILITY OF ONE OR MORE WATCHES...PERHAPS BY EARLY
   AFTERNOON.
   
   IN THE WAKE OF AN INITIAL SHORT WAVE IMPULSE NOW PIVOTING NORTHWARD
   INTO THE GREAT LAKES REGION...MID-LEVEL INHIBITION HAS BEEN WEAKENED
   ABOVE A MOISTENING PRE-FRONTAL CONFLUENT SOUTHERLY FLOW REGIME TO
   THE EAST OF THE MISSISSIPPI VALLEY CYCLONE.  MID-LEVELS ALREADY
   APPEAR TO BE WARMING FROM THE LOWER MISSISSIPPI VALLEY INTO THE
   WESTERN SLOPES OF THE CENTRAL/SOUTHERN APPALACHIANS.  HOWEVER...
   LATEST RUC GUIDANCE SUGGESTS INHIBITION MAY REMAIN FAIRLY NEGLIGIBLE
   ALONG AN AXIS FROM NORTHERN MISSISSIPPI THROUGH PARTS OF NORTH
   CENTRAL KENTUCKY.  AND...A ZONE OF MID-LEVEL MOISTENING/ LARGE-SCALE
   ASCENT IS EVIDENT IN WATER VAPOR IMAGERY RAPIDLY APPROACHING THIS
   REGION.  ADDITIONALLY... BREAKS IN CLOUD COVER LIKELY WILL BE
   SUFFICIENT TO ALLOW HEATING OF A BOUNDARY LAYER CHARACTERIZED BY
   UPPER 60S/LOWER 70S SURFACE DEW POINTS.
   
   THUS...IT SEEMS PROBABLE THAT THE RISK FOR AT LEAST SCATTERED
   BOUNDARY BASED THUNDERSTORM DEVELOPMENT WILL INCREASE THROUGH THE
   18-21Z TIME FRAME.  AS THIS OCCURS...SEVERE THREAT WILL INCREASE
   CORRESPONDINGLY WITHIN STRONG DEEP LAYER SHEAR FAVORABLE FOR
   SUPERCELLS...BETWEEN STRONG SOUTHWESTERLY POLAR AND SUBTROPICAL JET
   AXES.  ALTHOUGH LOW-LEVEL SHEAR MAY ONLY BE CHARACTERIZED BY WEAK
   CLOCKWISE TURNING WITH HEIGHT...HODOGRAPHS BENEATH 30-40 KT
   SOUTHWESTERLY 850 MB FLOW WILL BE FAVORABLE FOR TORNADOES...WHICH
   COULD BECOME STRONG.
   
   ..KERR.. 10/18/2007
   
   
   ATTN...WFO...JKL...ILN...LMK...OHX...BMX...HUN...PAH...MEG...JAN...
   
   33169092 34599057 35259010 36418932 37258857 38028741
   38788525 38578427 37328462 35308617 33778765 33088918