MESOSCALE PRECIPITATION DISCUSSION 0678
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
841 AM EDT MON SEP 19 2016
 
AREAS AFFECTED...EASTERN MD...DE...SOUTHEAST PA...CENTRAL.SOUTHERN
NJ...FAR SOUTHEAST NY/LONG ISLAND...SOUTHERN CT 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 191235Z - 191700Z
 
SUMMARY...HEAVY RAINS WILL CONTINUE OVER THE NEXT FEW HOURS...WITH
CONCERNS FOR SOME TRAINING CELLS. SOME FLASH FLOODING AND/OR
RUNOFF CONCERNS WILL BE POSSIBLE.

DISCUSSION...A WELL-DEFINED TROUGH OF LOW PRESSURE IS ORIENTED
FROM SOUTHERN VA NORTHEAST UP ACROSS THE DELMARVA AND UP TOWARD
LONG ISLAND. SURFACE DATA SUGGESTS A WEAK WAVE OF LOW PRESSURE
ADVANCING NORTHEAST INTO SOUTHERN NJ ALONG THE TROUGH AXIS WHICH
IS HELPING TO CONCENTRATE CONVECTION SOMEWHAT OVER THIS REGION. A
BROADER AREA OF BROKEN CONVECTION IS NOTED ELSEWHERE ALONG THE
BOUNDARY...INCLUDING A SW/NE AXIS OF SOME TRAINING CELLS OVER
PORTIONS OF EASTERN MD INTO CENTRAL/NORTHERN DE.

THE LARGE SCALE ENVIRONMENT FEATURES A MODESTLY DIVERGENT FLOW
PATTERN ALOFT ASSOCIATED WITH RIGHT-ENTRANCE REGION JET DYNAMICS
OUT AHEAD OF AN UPPER TROUGH MOVING THROUGH THE OH/TN VALLEYS.
MEANWHILE...A VERY MOIST COLUMN IS IN PLACE AS IDENTIFIED BY THE
12Z KLWX AND KWAL RAOB SOUNDINGS...AND ALSO THE CIRA-LPW PRODUCT
WHICH REFLECTS A SUBSTANTIAL AMOUNT OF MOISTURE IN THE 700/300MB
LAYER. THE DEGREE OF SURFACE CONVERGENCE NEAR THE AFOREMENTIONED
TROUGH AND LARGER SCALE ASCENT IS LIKELY TO MAINTAIN THE THREAT
FOR SW/NE ORIENTED BANDS OF CONVECTION THROUGH THE MORNING HOURS
OVER PORTIONS OF THE MID-ATLANTIC COASTAL PLAIN. ONE MITIGATING
FACTOR IS THE LACK OF STRONGER INSTABILITY FOR MORE ORGANIZED AND
STRONGER CONVECTION...BUT THE DEEP MOIST COLUMN WILL STILL FAVOR
INTENSE RAINFALL RATES...THAT MAY EXCEED 2 INCHES/HR GIVEN
EFFICIENT WARM RAIN PROCESSES.

ADDITIONAL RAINFALL AMOUNTS OF 3 TO 5 INCHES WILL BE POSSIBLE.
GIVEN THE TRAINING CELL POTENTIAL...AT LEAST SOME POTENTIAL FOR
FLASH FLOODING AND/OR RUNOFF PROBLEMS WILL CONTINUE THROUGH THE
MORNING.

ORRISON

ATTN...WFO...AKQ...BOX...LWX...OKX...PHI...

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

LAT...LON   41587237 41437161 41227162 40927220 40447338 
            39777403 39267432 38857485 38157537 38097613 
            38617655 39327636 39687599 40217539 40657467 
            41067394 41377304