MESOSCALE DISCUSSION 1315 NWS STORM PREDICTION CENTER NORMAN OK 0733 PM CDT FRI JUN 29 2012 AREAS AFFECTED...CNTRL/ERN IA...NRN/CNTRL IL...NWRN IND CONCERNING...SEVERE THUNDERSTORM WATCH 437... VALID 300033Z - 300200Z THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 437 CONTINUES. SUMMARY...THE SVR THREAT ACROSS WW 437 WILL LIKELY HAVE DIMINISHED BY THE SCHEDULED EXPIRATION TIME OF 02Z. REMAINING VALID PORTIONS OF THE WW BEHIND ERN/SRN-FLANKING OUTFLOW BOUNDARY MAY BE CANCELLED PRIOR TO EXPIRATION TIME. AREAS DOWNSTREAM ACROSS NRN/CNTRL IL INTO NWRN IND WILL CONTINUE TO BE MONITORED FOR ADDITIONAL WW ISSUANCE THROUGH THE NIGHT. DISCUSSION...CONVECTION HAS BECOME LARGELY DISORGANIZED ACROSS WW 437 DURING THE LAST COUPLE OF HOURS...AFTER OUTFLOW FROM THE SMALL SVR COMPLEX THAT CROSSED THE CEDAR RAPIDS AREA SURGED AHEAD OF PARENT CONVECTION. THIS OUTFLOW BOUNDARY NOW EXTENDS WSWWD FROM 35 ENE MOLINE IL TO 45 E LAMONI IA. ISOLATED ELEVATED CONVECTION WITHIN 30 MILES N/W OF THIS BOUNDARY MAY POSE A MARGINAL SVR THREAT...THOUGH THIS THREAT MAY SUBSIDE AS OUTFLOW SURGES AHEAD OF THE CONVECTION. FARTHER WEST...WEAK ISENTROPIC ASCENT ATOP THE COLD POOL IS SUPPORTING SCATTERED ELEVATED STORMS INTO WRN PARTS OF THE WW AREA...AND AN ISOLATED MARGINALLY SVR HAIL THREAT CANNOT BE RULED OUT. OVERALL...HOWEVER...THIS LOOSELY ORGANIZED CONVECTIVE SYSTEM APPEARS TO BE EXHIBITING MORE ANAFRONTAL CHARACTERISTICS...WITH A DIMINISHING SVR THREAT ANTICIPATED THROUGH 02Z. MEANWHILE FOR DOWNSTREAM AREAS...A CONVECTIVELY AUGMENTED BOUNDARY IS ADVANCING NEWD ACROSS IL INTO IND...WITH VERY UNSTABLE AIR OBSERVED TO ITS SOUTH -- REF. CENTRAL ILLINOIS 00Z RAOB FEATURING 3260 J/KG OF MLCAPE /THOUGH WITH SUBSTANTIAL DRY AIR ALOFT/. HOWEVER...MODEST MIXED-LAYER INHIBITION IS PRESENT...AND IS FORECAST TO INCREASE THROUGH THE NIGHT OWING TO NOCTURNAL/DIABATIC COOLING. REGARDLESS...WITH A NOCTURNAL INCREASE IN WAA COMMENSURATE WITH STRENGTHENING WSWLY 700-850 MB FLOW/STRENGTHENING BOUNDARY-LAYER WIND MAXIMUM...ADDITIONAL STORMS -- LIKELY INITIALLY ELEVATED -- MIGHT DEVELOP ACROSS PARTS OF IL/IND. SHOULD A SUFFICIENT NUMBER OF STORMS MATERIALIZE WITH COLD POOL DEVELOPMENT/UPSCALE GROWTH ENSUING...A MORE WIDESPREAD SVR THREAT WARRANTING WW ISSUANCE COULD CONDITIONALLY DEVELOP LATER IN THE NIGHT DOWNSTREAM OF WW 437 PROVIDED 30-45 KT OF EFFECTIVE BULK SHEAR. HOWEVER...LARGE UNCERTAINTY IN THIS THREAT REMAINS OWING TO THE AFOREMENTIONED INHIBITION/LACK OF STRONGER DEEP FORCING FOR ASCENT.
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