EXCESSIVE RAINFALL DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 951 AM EDT SAT APR 30 2011 ...VALID 15Z SAT APR 30 2011 - 12Z SUN MAY 01 2011... ...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL... SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM POF PAH MEM GLH OSA AQR RUE POF. MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM LLQ LBR HOT ARG HKA LLQ. ...LWR MS INTO ARKLATX... EXPANDED THREAT REGION THIS MRNG FOR TWO REASONS. LATEST GUID IS INDICATING MORE SUPPORT FOR CNVCTN FARTHER S AND 30/12Z OBSVD PWS ARE HIER THAN THE LATEST 06Z NAM/GFS FCSTS. SPLIT FLOW REGIME IS DVLPG OVR THE REGION WITH A DEEP VORTEX LIFTG NEWD FM THE NRN PLNS...WHILE A TRAILING TROF BREAKS AWAY AND MOVES INTO THE 4-CORNERS REGION TNGT...THEN PROGRESSES EWD OVR THE NEXT FEW DAYS. UPR FLOW IS ALRDY SLGTLY DIFL AND IS FCST TO BCM MORE DIFL THRU THE PD...WITH AN EXPANDING AREA OF UPR DVRG AND ASSOCD STG/DEEP LYRD ASCENT AS THE REGION COMES UNDER THE RGT ENTRNC REGION OF THE UPR JET. LATEST SATL/GPS DERIVED PW DATA SHOWS A RAPIDLY EXPANDING TONGUE OF DEEP MSTR OVR TX...WITH STG LINKS TO THE EPAC/GULF AND CARIBBEAN. MDLS ARE TOO SLOW WITH THE NWD MSTR TRANSPORT/FLUX. PWS ARE FCST TO INCRS TO ARND 1.50 INCHES...BUT THIS COULD BE HIER PER SLOW MDL RESPONSE THIS MRNG. PW ANOMALIES SHLD BUILD TO NEAR TWO STDS ABV NRML. THE DVLPMENT OF A MOD/STG LLJ TNGT WL HELP INCRS MSTR TRANSPORT INTO THE REGION WITH ANOMALIES BUILDING TO 3-4 STDS ABV NRML. SFC BNDRY DRAPED ACRS THE CNTRL/SRN PLNS WL PUSH SEWD AND LKLY STALL/SLOW ITS FORWARD PROGRESS...WHILE THE STG SRLY FLOW OVER-RIDES THE BNDRY. MDLS INDICATE AN IMPRVS 8H THETA-E RDG DVLPG ACRS THE REGION IN A SW-NE ORIENTATION BY THIS EVE...BUT THIS TAKES ON A MORE W-E ORIENTATION LATER TNGT AS THE LLJ VEERS. THIS COULD RESULT IN AN INCRSD THREAT FOR TRAINING ACRS THE REGION LATER TNGT. MDL FCST SOUNDINGS ARE ALL SHOWG VRY FAVORABLE PROFILES FOR HVY RNFL WITH TALL SKINNY CAPES AND MIDLVL LAPSE RATES ARND 6 C/KM. INITIAL SHRTWV LIFTG NEWD ACRS TX THIS MRNG IS FIRING SCT ELEV CNVCTN WHICH SHLD PUSH NEWD...XPCT ADDTNL CVNCTN TO FIRE LATER THIS AFTN/EVE IN CONJUNCTION STGR SFC HEATG AND ADDTNL SHRTWV ENERGY. EXPERIMENTAL HI-RES DENSITY PLOTS OF RNFL EXCEEDING FFG ARE SHOWING THE BIGGEST THREAT OVR THE CONFLUENCE REGION OF THE OH/MS RIVERS WHERE FFG IS LOWEST...BUT THERE ARE ALSO SOME RISK FARTHER SW WHERE TRAINING COULD DVLP TNGT. THE MAIN THREAT FOR ORGANIZED HVY RNFL SHLD BE AFTER 01/00Z WITH LCL 1-2 INCH HRLY RATES AND PSBL ISOLD 4-5 INCH TOTALS BY SUN MRNG. ECKERT Q$$