Mesoscale Precipitation Discussion 0893
NWS Weather Prediction Center College Park MD
147 PM EDT Tue Sep 25 2018

Areas affected...Eastern PA...northern NJ...southern
NY...western/central CT

Concerning...Heavy rainfall...Flash flooding likely

Valid 251746Z - 252216Z

Summary...Strong frictional convergence along the coast will
enhance thunderstorms in the area and lead to potential
training/repeating rounds resulting in flash flooding.

Discussion...Exiting shortwave seen in recent water vapor imagery
combined with strong frictional convergence has led to a large
shield of steady to moderate rain with embedded pockets of heavy
rainfall moving across portions of NJ, NY, and western CT. The
environment is characterized by anomalous moisture with PWATs of
1.8 to 1.9 inches. Instability is weak presently but will be
increasing over the coming hours.

Recent observations show 1-hour totals of 1 to 1.5 inches across
the NYC metro area and 3-hour totals of 2.5 to 3 inches, where FF
warnings are presently in the effect. The threat of flash flooding
will continue due to training convection potential and also shift
into western/central CT per latest runs of the HRRR. Additional
weaker cells and moderate overrunning rainfall will add an
additional 1 to locally 2 inches of rain through this afternoon.

Additional thunderstorms will be possible further southwest into
NJ and portions of eastern PA with more favorable instability
expected this afternoon and interactions with the surface front
draped across the area, potentially affecting the Philadelphia
metro where FFG values are lower.

Taylor

ATTN...WFO...ALY...BOX...OKX...PHI...

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

LAT...LON   42027204 41497178 41107284 40607387 40207434
            40017451 39577524 39767564 40107566 40817507
            41247463 41587385 41897303