230
AWUS01 KWNH 301754
FFGMPD
NJZ000-PAZ000-DEZ000-MDZ000-302200-
MESOSCALE PRECIPITATION DISCUSSION 0559
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
154 PM EDT MON JUN 30 2025
AREAS AFFECTED...SOUTHEAST PENNSYLVANIA, SOUTHERN AND CENTRAL NEW
JERSEY, AND DELAWARE
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 301752Z - 302200Z
SUMMARY...ISOLATED TO SCATTERED THUNDERSTORMS WILL CONTINUE EARLY
THIS AFTERNOON IN SOUTHEAST PENNSYLVANIA, SOUTHERN AND CENTRAL NEW
JERSEY, AND PORTIONS OF DELAWARE. AT TIMES, THESE THUNDERSTORMS
MAY MOVE VERY SLOWLY OR BECOME NEARLY STATIONARY, WHICH WOULD LEAD
TO LOCALIZED AREAS OF VERY HEAVY RAINFALL AND POTENTIALLY FLASH
FLOODING, ESPECIALLY IF THAT OCCURS OVER URBAN AREAS. THE THREAT
OF FLASH FLOODING SHOULD BE HIGHEST THROUGH AROUND 5-6 PM EDT, BUT
COULD LAST LONGER.
DISCUSSION...SEVERAL WELL-ORGANIZED THUNDERSTORMS HAVE DEVELOPED
IN AN AREA OF STRONG INSTABILITY FROM SE PA INTO S NJ AND DE.
HI-RES MODEL GUIDANCE HAS STRUGGLED WITH THIS, BUT THE
EXPERIMENTAL RRFS MAY BE DOING THE BEST AS OF 1730Z. IT SHOWS
ORGANIZED BUT ISOLATED CELLS OR SMALL CLUSTERS PERSISTING ACROSS
THE AREA THROUGH ABOUT 22Z (6 PM EDT), ANCHORING AT TIMES TO SEA
BREEZE BOUNDARIES OR A FRONT DRAPED ACROSS THE REGION. THERE IS
SOME EVIDENCE OF THIS ALREADY HAPPENING WITH A THUNDERSTORM NEAR
COASTAL SUSSEX COUNTY, DELAWARE, AND IT COULD CONCEIVABLY HAPPEN
WITH OTHER STORMS ELSEWHERE IN THE REGION. THE ENVIRONMENT IS VERY
SUPPORTIVE OF INTENSE RAIN RATES WITH PWS NEAR OR ABOVE 2 INCHES
(ABOVE THE 95TH PERCENTILE FOR LATE JUNE) AND VERY STRONG
INSTABILITY. THEREFORE, HOURLY RAINFALL IN EXCESS OF 2 INCHES IS
PLAUSIBLE AND IF STORMS STALL IN A GIVEN LOCATION FOR OVER AN
HOUR, RAPID DEVELOPMENT OF RAINFALL MAXIMA OVER 3-4 INCHES WOULD
BE POSSIBLE. IN THESE AREAS, FLASH FLOODING COULD DEVELOP,
PARTICULARLY IF IT INTERSECTS WITH URBAN AREAS.
THE OUTLOOK BEYOND 21-22Z (5-6 PM EDT) IS LESS CERTAIN, AS THE
HI-RES MODEL GUIDANCE DOESN'T LOOK TO BE COMPLETELY RELIABLE. IT
SEEMS DOUBTFUL THAT ALL THE INSTABILITY IN THE REGION WOULD BE
COMPLETELY EXHAUSTED BY THAT TIME, SO A CONTINUATION OF THE FLASH
FLOOD THREAT COULD CONTINUE INTO THE EARLY EVENING. HOWEVER, THE
THREAT MAY SHIFT TO AREAS JUST OUTSIDE WHERE INITIAL DEVELOPMENT
IS OCCURRING.
LAMERS
..PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT
ATTN...WFO...AKQ...CTP...PHI...
ATTN...RFC...RHA...NWC...
LAT...LON 40897571 40737499 40397396 39817396 39407463
38997486 38377496 38457537 38977564 39537578
39827614 40147705 40807667
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