EXCESSIVE RAINFALL DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 947 AM EDT SAT APR 16 2011 ...VALID 15Z SAT APR 16 2011 - 12Z SUN APR 17 2011... ...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL... SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM 10 NNE ELZ 15 NNW ELM 10 NE ITH 30 SSW UCA 40 WSW SCH 25 SW ALB 30 WSW PSF 30 SW PSF 20 NE POU 10 NW HPN NYC 15 SSW EWR 10 SSE TTN 15 WNW PHL 20 NNE APG 15 N MTN 10 W BWI DCA KW66 OMH 20 NW FVX 20 ESE ROA 15 S ROA 20 SSE BCB 20 ENE HLX HLX 10 E MKJ 10 SSW BLF 10 N BLF 15 NE BKW 25 S 48I 10 NW 48I 25 WNW W22 25 WNW CKB 25 SSW AFJ AFJ 15 NNE AGC 20 ENE BTP 20 NW DUJ BFD 15 W ELZ 10 NNE ELZ. 15Z UPDATE.. MADE SOME SLIGHT EWD ADJUSTMENT TO SLIGHT RISK AREAS WHERE EXISTING FF GUIDANCE VALUES ARE RATHER LOW. OTHERWISE..EARLIER FORECAST REASONING STILL VALID FOR POTNL FLOODING PROBLEMS THRU THE AFTN/EVENING ACRS THIS REGION. SATL/UA DATA SHOWS FAIRLY VIGOROUS VORT MOVING THROUGH BASED OF UPR TROF THRU TN. IN ADVANCE OF THIS FEATURE...CONVECTION HAS INCREASED RAPIDLY OVER THE PAST FEW HRS THRU WV/ERN OH..WHILE AREA OF GENL RAIN AND HEAVIER SHWRS HAVE INCREASED EAST OF THIS AREA IN BROAD WAA PATRN ACRS THE MID ATLC REGION NWD INTO NY. EXPECT THIS GENL INCREASING RAINFALL TREND TO CONTINUE THIS AFTN WITH MODELS INDICATING RAINFALL AMOUNTS OF 1-2+ INCHES DURG THE PD WHICH LOOKS QUITE REASONABLE. SULLIVAN PREVIOUS DISCUSSION FOLLOWS.... THE MID/UPR LOW OVR THE CNTRL U.S. WL BEGIN TO GRADUALLY FILL AND TAKE ON A MORE NEG TILT AS IT LIFTS NEWD INTO THE NRN MID ATLC/SRN NEW ENG REGION BY SUN MRNG. STG INFLO OF GULF AND EVENTUALLY ATLC MSTR WL CONT AHD OF THIS H5 TROF..ON A SLY LLJ EXCEEDING 60KTS..WHICH WL BRING PWS BTWN 1.00-1.25 INCHES AS FAR N AND E AS THE NRN MID ATLC/SRN NEW ENG REGION. COMBO OF THIS INCREASE IN MSTR AND STG ORGANIZED LRG SCALE LIFT FM SIGNIFICANT HGT FALLS/MID LVL DYNAMICS AND FAVORABLE UPR JET DYNAMICS..WL SUPPORT WIDESPREAD MDT TO HVY RAINS FM THE SERN STATES NWD INTO NEW ENG. RATHER LOW FF GUIDANCE VALUES ARE A PRIMARY CONCERN WITHIN THE THREAT AREA..WITH XPCD RNFL AMTS OF 1-2+ INCHES DURG THIS PD POTNLY RESULTING IN SOME RUNOFF/FLOODING ISSUES. TERRY $$