MESOSCALE PRECIPITATION DISCUSSION 0412
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
413 AM EDT FRI JUL 06 2018

AREAS AFFECTED...ERN PA INTO NJ/SRN NY

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 060812Z - 061215Z

SUMMARY...FLASH FLOODING WILL BE POSSIBLE ACROSS PORTIONS OF THE
PA/NJ BORDER INTO NJ AND SOUTHERN NY THROUGH 12Z. THERE WILL BE
RAINFALL POTENTIAL OF 1-2 IN/HR AND 2-3 INCHES IN 2 HOURS WHICH
MAY OVERLAP WITH URBAN ENVIRONMENTS AND THE MORNING RUSH HOUR.

DISCUSSION...GOES 16 5-MINUTE "CLEAN WINDOW" INFRARED IMAGERY
SHOWED RAPIDLY COOLING CLOUD TOPS OVER SOUTHEASTERN PENNSYLVANIA
BETWEEN 07-08Z. 08Z RADAR DATA FROM KDIX SHOWED HIGHER
REFLECTIVITY VALUES SLOWLY MOVING EAST INTO MONTGOMERY AND BUCKS
COUNTY...WITH A COUPLE OF WUNDERGROUND.COM OBSERVATIONS SHOWING
ABOUT 0.5 INCHES OF RAIN IN A 10-15 MINUTE TIME SPAN NEAR AND EAST
OF READING BETWEEN 07-08Z...AND RADAR ESTIMATES OF 1.5 IN/HR ALONG
THE BERKS/MONTGOMERY COUNTY LINE.

THE SPC MESOANALYSIS AND 07Z RAP INDICATED AN AXIS OF 1000-2000
J/KG MLCAPE EXTENDED FROM THE DELMARVA PENINSULA INTO NJ AND LONG
ISLAND WITH RAP ANALYSIS SOUNDINGS SHOWING TALL/SKINNY CAPE
PROFILES ACROSS CENTRAL NJ. FLOW IS UNIDIRECTIONAL FROM THE LFC TO
EL WITH VAD WIND PLOT OBSERVED 850 MB FLOW MATCHING OR EXCEEDING
MEAN INDIVIDUAL STORM MOTIONS OFF TO THE ENE AT ROUGHLY 20 KT.
ALOFT...FLOW AT 250 MB IS MODERATELY DIFFLUENT WHICH SHOULD HELP
SUPPORT LIFT THROUGH THE COLUMN.

GIVEN SUFFICIENT MOISTURE/INSTABILITY IS IN PLACE AND SHORT TERM
RAP FORECASTS SHOW 850 MB FLOW INCREASING SLIGHTLY OVER THE NEXT
COUPLE OF HOURS...THE SMALL CLUSTER OF THUNDERSTORMS OVER
SOUTHEASTERN PENNSYLVANIA IS EXPECTED TO CONTINUE ADVANCING OFF
TOWARD THE EAST-NORTHEAST WITH PERIODS OF TRAINING. 2-3 INCHES IN
A 2 HOUR TIME FRAME WILL BE POSSIBLE WHICH MAY CAUSE RUNOFF
PROBLEMS ACROSS PORTIONS OF THE PA/NJ BORDER INTO THE NYC METRO
THROUGH 12Z. GIVEN THE URBAN NATURE OF THESE LOCATIONS AND THE
BEGINNING OF THE MORNING RUSH HOUR...FLASH FLOODING COULD BECOME
AN INCREASING CONCERN.

OTTO

ATTN...WFO...OKX...PHI...

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

LAT...LON   41067238 40247251 39947379 39927509 40047568
            40407569 40787520 41007389