MESOSCALE PRECIPITATION DISCUSSION 0157
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1152 PM EDT THU JUL 11 2013
 
AREAS AFFECTED...CNTRL/NRN VA...DC...INTO CNTRL MD 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 120351Z - 120951Z
 
SUMMARY...VERY SLOW MOVING CONVECTION WITH HEAVY RAINFALL RATES
SHOULD CONTINUE TO POSE A FLASH FLOOD THREAT THROUGH THE NIGHT
AHEAD OF A SLOW MOVING UPPER LOW.

DISCUSSION...NOCTURNAL CONVECTION ALONG AND AHEAD OF A
QUASI-STATIONARY FRONT...EXTENDING SWWD FROM LONG ISLAND THROUGH
CNTRL MD AND WRN VA AS OF 03Z...HAS INCREASED IN COVERAGE OVER THE
PAST HOUR WITH 1 HR RAINFALL RATES OF 1-2 IN/HR BASED ON
OBSERVATIONS AT KIAD AND DUAL-POL RADAR ESTIMATES. THESE STORMS
ARE DEVELOPING AHEAD OF A SLOW MOVING MID-UPPER LEVEL LOW
CURRENTLY OVER OHIO...AND WITHIN THE RIGHT ENTRANCE REGION OF A
70-90 KT UPPER JET SEEN ON 00Z RAOB DATA ACROSS THE NORTHEAST. 

AS THE UPPER LOW SLOWLY SINKS SWD ACROSS OHIO OVER THE NEXT
SEVERAL HOURS...DEEPER MOISTURE CHARACTERIZED BY PRECIPITABLE
WATER VALUES NEAR 2 INCHES OBSERVED OVER SERN VA WILL SLOWLY BE
PULLED NORTH WITH THIS PIVOTING TREND ALREADY BEING OBSERVED ON
WATER VAPOR. GIVEN TRENDS AND QPF OUTPUT FROM A NUMBER OF SHORT
TERM HI-RES MODELS (HRRR...HRW ARW...NSSL WRF)...THERE IS MEDIUM
TO HIGH CONFIDENCE IN HEAVY RAINS CONTINUING THROUGH THE NIGHT AND
SLOWLY SPREADING EAST AHEAD OF THE UPPER LOW. FLASH FLOODING IS
ALREADY OCCURRING BASED ON A NUMBER OF RECENT LOCAL STORM REPORTS
DESPITE HIGHER FFG VALUES OF 2-3 IN/HR ACROSS NRN PORTIONS OF THE
THREAT AREA.

OTTO  

ATTN...WFO...PHI...AKQ...LWX...RNK...

ATTN...RFC...MARFC...SERFC...

LAT...LON   38277683 37247765 36707876 36957938 37397959 37907967
            38517913 38957855 39297806 39587700 39537593 38927598
            38277683