MESOSCALE PRECIPITATION DISCUSSION 0183
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
532 PM EDT SUN JUL 28 2013
 
AREAS AFFECTED...EXTREME EASTERN MD...EXTREME SOUTHEASTERN
PA...DE...NJ...SOUTHEAST NY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 282130Z - 290030Z
 
SUMMARY...SLOW-MOVING LINEAR CONVECTIVE BAND WITH EMBEDDED
BACK-BUILDING CELLS WILL LIKELY CONTINUE THE NEXT COUPLE OF HOURS.
INTENSE RAINFALL RATES WILL BE CONDUCIVE FOR SHORT-TERM FLASH
FLOODING.

DISCUSSION...LATEST SAT/RADAR IMAGERY SHOWS A SSW/NNE ORIENTED
BAND OF CONVECTION SITUATED FROM NRN DE AND THE ADJACENT DELAWARE
RIVER UP ACROSS NRN NJ AND ENCROACHING ON FAR SERN NY. CLOUD TOP
TEMPS WITH ESP THE NRN PORTION OF THIS BAND HAVE BEEN GRADUALLY
COOLING...AND THERE IS A RATHER WELL-DEFINED OVERSHOOTING TOP WEST
OF SOMERSET NJ OF NOTE OVER THE LAST 30 MINUTES. MUCH OF THIS
APPEARS TO BE IN RESPONSE TO LARGER SCALE HEIGHT FALLS APPROACHING
FROM THE OH VLY AND INTERACTING WITH A FAIRLY WELL-DEFINED LOW
LEVEL CONVERGENCE ZONE OVER MUCH OF WRN NJ AND EXTENDING SOUTH
DOWN INTO NRN DE AND EVEN FAR ERN MD. ADDITIONALLY...THE LATEST
RAP ANALYSIS SHOWS A MODERATELY STRONG INSTABILITY AXIS INVOF THE
AXIS OF STRONGEST LOW LEVEL CONVERGENCE...WITH SBCAPE VALUES CLOSE
TO 2000 J/KG LOCALLY.

FARTHER SOUTH...CONVECTION CONTINUES TO RELOAD AND BACKBUILD OVER
SRN NJ...AREAS ADJACENT TO THE DELAWARE RIVER AND INTO NRN
DE...WHERE LATEST VIS ACTUALLY DEPICTS THE SRN TAIL OF THE
AFOREMENTIONED CONVERGENCE ZONE. CLOUD STREETS INDICATIVE OF AN
UNSTABLE BOUNDARY LYR ARE SEEN ADVANCING INTO THIS REGION.

IT SHOULD BE NOTED THAT WV IMAGERY SUGGEST A WEAK SHORTWAVE
IMPULSE APPROACHING THE SRN PORTION OF THIS CONVECTIVE BAND AND
THIS WILL LIKELY FOSTER ADDITIONAL BACK-BUILDING AND TRAINING OF
CONVECTION OVER AREAS OF ESP NRN DE AND INTO SRN AND CNTRL NJ
GIVEN THE UNSTABLE ENVIRONMENT. RAINFALL RATES ALREADY OF 2.5 TO 3
INCHES/HR HAVE BEEN NOTED...AND REGIONAL RAINFALL TOTALS IN EXCESS
OF 5 INCHES ARE EXPECTED FOR THE EVENT. GIVEN THE SLOW-MOVING
CONVECTIVE BAND AND BACK-BUILDING OF CELLS AND TRAINING
THREAT...THERE IS A SERIOUS RISK OF FLASH FLOODING THE NEXT FEW
HOURS.

ORRISON

ATTN...WFO...OKX...ALY...PHI...AKQ...

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

LAT...LON   40217522 40617489 41287453 41507408 41387370 40837372
            40207405 39497456 38857514 38617548 38517582 38777612
            39697559 40217522