MESOSCALE DISCUSSION 0475
   NWS STORM PREDICTION CENTER NORMAN OK
   0547 PM CDT TUE APR 19 2011
   
   AREAS AFFECTED...E-CNTRL/S-CNTRL MO...CNTRL IL
   
   CONCERNING...TORNADO WATCH 154...
   
   VALID 192247Z - 200015Z
   
   THE SEVERE WEATHER THREAT FOR TORNADO WATCH 154 CONTINUES.
   
   LATEST SURFACE ANALYSIS PLACES LOW PRESSURE 45 NNW STL WITH A WARM
   FRONT EXTENDING EWD FROM THE LOW TO NEAR SPI AND THEN EWD INTO WRN
   IND 30 ENE HUF. A COLD FRONT EXTENDS S-SWD FROM THE LOW TO 10 NNW
   TBN TO 15 SSE OF UMN. THE MOST VIGOROUS AND WIDESPREAD CONVECTIVE
   DEVELOPMENT /INCLUDING DISCRETE AND SEMI-DISCRETE SUPERCELLS/ OVER
   THE PAST HOUR HAS BEEN NOTED IN THE ERN SEMICIRCLE OF THE LOW WITHIN
   60 NM OF THE LOW CENTER. BACKED SFC FLOW IN THIS REGION...ESPECIALLY
   INVOF THE WARM FRONT...IS SUPPORTING STRONG LOW-LEVEL VERTICAL WIND
   SHEAR AND EFFECTIVE SRH VALUES OF 300-400 M2/S2. THE SFC LOW IS
   FORECAST TO SHIFT E-NEWD INTO CNTRL IL DURING THE NEXT COUPLE OF
   HOURS...WHERE PRESSURE FALLS AROUND 2 MB PER 2 HRS HAVE BEEN NOTED.
   CORRESPONDINGLY...THE GREATEST THREAT FOR SUPERCELLS WITH DMGG WINDS
   AND VERY LARGE HAIL /SUPPORTED BY MLCAPE VALUES AOA 2000 J PER KG
   AND STRONG CLOUD-BEARING WIND SHEAR/ WILL OCCUR WITHIN A 60-NM-WIDE
   AREA CENTERED ALONG A LINE FROM 45 WSW STL TO 5 ESE DEC THROUGH 00Z.
   THIS INCLUDES THE ST LOUIS METRO AREA /ESPECIALLY NRN SECTIONS/
   BETWEEN 23Z AND 00Z. TORNADOES WILL REMAIN A CONCERN...AS
   WELL...ESPECIALLY WITH ANY SUPERCELLS THAT CAN REMAIN DISCRETE AND
   MOVE EWD NEAR THE WARM FRONT. 
   
   FARTHER SOUTH ALONG THE COLD FRONT...THE PRESENCE OF SOME CINH HAS
   RESULTED IN FAIRLY MORE ISOLATED COVERAGE OF STORMS...EXCEPT IN
   S-CNTRL MO WHERE MID-LEVEL ASCENT IS MORE PRONOUNCED. THIS ACTIVITY
   WILL MOVE NEWD AROUND 35-40 KT WHILE TRAVERSING STRONG INSTABILITY
   AND EFFECTIVE BULK SHEAR MAGNITUDES AOA 45 KT...WITH BOTH LINEAR AND
   DISCRETE SUPERCELL MODES FAVORED. DMGG WINDS...VERY LARGE HAIL...AND
   TORNADOES WILL REMAIN THREATS WITH EFFECTIVE SRH VALUES OF 200-300
   M2/S2.
   
   ..COHEN.. 04/19/2011
   
   
   ATTN...WFO...PAH...ILX...LSX...SGF...
   
   LAT...LON   36639334 37029352 37889301 39219169 40078987 40148779
               39558755 38818782 38598878 38208970 37219104 36669171
               36639334