MESOSCALE PRECIPITATION DISCUSSION 0391
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1253 AM EDT MON JUL 27 2015
 
AREAS AFFECTED...SOUTHEAST PA...NORTHERN MD 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 270452Z - 270700Z
 
SUMMARY...DISORGANIZED AREA OF SHOWERS AND THUNDERSTORMS OVER
SOUTHEAST PA WILL CONTINUE TO PRODUCE SOME VERY HEAVY RAINFALL
AMOUNTS IN A SHORT PERIOD OF TIME...WITH THE POTENTIAL FOR
CONVECTION OVER NORTHERN MD TO PRODUCE LOCALLY HEAVY RAINFALL. 

DISCUSSION...SHOWERS AND THUNDERSTORMS OVER SOUTHEAST PA HAVE
BECOME MORE NUMEROUS IN A REGION NEAR AN AXIS OF HIGHEST THETAE
WHICH HAPPENED TO BE ROUGHLY COINCIDENT WITH THE AXIS OF HIGHEST
PRECIPITABLE WATER VALUES.  A SLOW MOVING MID LEVEL SHORTWAVE HAS
BEEN MOVING ACROSS WESTERN AND CENTRAL PA WILL CONTINUE TO PROVIDE
SYNOPTIC SCALE LIFT AS IT APPROACHES SOUTHEAST PA.

RADAR IMAGERY THROUGH 0430Z HAS SHOWN CONVECTION ALOFT DEVELOPING
ACROSS NORTHERN MD.  THESE SHOWERS AND STORMS WILL ALSO GRADUALLY
BE MOVING TOWARDS THE AXIS OF HIGHEST THETAE AND PW.  AS A
RESULT...THINKING IS THAT THESE STORMS WILL ALSO HAVE THE
POTENTIAL FOR PRODUCING SOME INTENSE RAINFALL RATES AS THEY MOVE
SLOWLY TOWARDS THE EAST AND SOUTH. SOME REPORTS OF FLASH FLOODING
HAVE ALREADY OCCURRED IN RESPONSE TO RAINFALL RATES OF NEARLY 2.5
INCHES IN UNDER AN HOUR.  THINKING IS THAT THE FLASH FLOOD RISK
WILL CONTINUE FOR A COUPLE MORE HOURS.

THE MODEL GUIDANCE HAS NOT HAD A VERY GOOD HANDLE ON THE EVOLUTION
OF THIS CONVECTION.  THE CURRENT THINKING IS THAT THE STORMS
SHOULD CONTINUE FOR THROUGH 08Z BEFORE SETTLING DOWN AS LOW LEVELS
BECOME INCREASINGLY STABLE OVERNIGHT.  

BANN

ATTN...WFO...CTP...LWX...PHI...

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

LAT...LON   40727541 40627502 40207493 39857509 39497553 
            39307610 39087652 39217719 39277739 39517755 
            39877758 40137694 40437625 40627588