Posted by JAC on 4/30/2009, 7:45 am

DAY 4-8 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0400 AM CDT THU APR 30 2009 VALID 031200Z - 081200Z ...DISCUSSION... MODELS HAVE DEMONSTRATED RUN TO RUN CONSISTENCY THE PAST TWENTY FOUR HOURS IN HANDLING NEXT SRN STREAM SHORTWAVE TROUGH FORECAST TO MOVE THROUGH THE SRN PLAINS AND INTO THE LOWER MS VALLEY SUNDAY AND SUNDAY NIGHT. MODEST TIMING AND AMPLITUDE DIFFERENCES STILL EXIST BUT ARE NOT AS SIGNIFICANT AS PREVIOUS RUNS. THE ECMWF IS LOWER IN AMPLITUDE AND FASTER THAN THE GFS AND UKMET...AND MODEST SPREADS EXIST AMONG ENSEMBLE MEMBERS THROUGH DAY 4. DAY 4...A MOIST AND UNSTABLE WARM SECTOR WILL EXIST FROM CNTRL AND ERN TX THROUGH THE LOWER MS VALLEY TO THE SOUTH OF STALLED FRONTAL BOUNDARY. MUCH OF THIS WARM SECTOR SHOULD BE RELATIVELY UNDISTURBED SINCE ANY ONGOING CONVECTION WILL LIKELY BE IN COOL SECTOR. STORMS SHOULD REDEVELOP ALONG AND AHEAD OF THE COLD FRONT DURING THE DAY WITHIN ZONE OF LARGE SCALE LIFT ATTENDING THE PROGRESSIVE SHORTWAVE TROUGH. INCREASING SHEAR PROFILES ACCOMPANYING THIS FEATURE WILL SUPPORT ORGANIZED STORMS INCLUDING SUPERCELLS. THE SEVERE THREAT WILL SHIFT EAST INTO THE LOWER MS AND TN VALLEY DURING THE EVENING AND OVERNIGHT. DAY 5-6...ENSEMBLE SPREADS INCREASE AND DETERMINISTIC MODELS BECOME MORE DISPERSIVE BY DAY 5. ECMWF DE-AMPLIFIES INITIAL SHORTWAVE TROUGH OVER THE OH VALLEY CONFLUENT FLOW REGIME MUCH MORE RAPIDLY THAN THE GFS AND AMPLIFIES AN UPSTREAM TROUGH ACROSS THE PLAINS BY DAY 6. THE ECMWF WOULD SUPPORT A POTENTIAL SEVERE WEATHER OUTBREAK BY DAY 6 ACROSS A PORTION OF THE PLAINS AND MID MS VALLEY REGION. HOWEVER...DUE TO THE VERY LARGE SPREADS IN MODEL SOLUTIONS WILL NOT INCLUDE AN OUTLOOK BEYOND THE DAY 4 PERIOD AT THIS TIME. ..DIAL.. 04/30/2009