Graphic for MPD #0451

MESOSCALE PRECIPITATION DISCUSSION 0451
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
503 PM EDT THU JUL 06 2017

AREAS AFFECTED...SOUTHERN PA/NORTHERN WV/MD/DE/SOUTHWESTERN NJ...

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

VALID 062103Z - 070118Z

SUMMARY...WITHIN A SUBSTANTIAL MOISTURE PLUME STREAMING OFF THE
WESTERN ATLANTIC...CELLULAR CONVECTION HAS SHOWN A TENDENCY TO
BECOME STATIONARY ACROSS SECTIONS OF THE MID-ATLANTIC. THIS
BEHAVIOR SHOULD CONTINUE GIVEN WEAK STEERING FLOW IN CONJUNCTION
WITH HIGHLY EFFICIENT UPDRAFTS. HOURLY RAINFALL RATES SHOULD
EASILY REACH THE 1 TO 2 INCH RANGE WHICH WILL ENHANCE THE FLASH
FLOOD RISK ACROSS THE REGION.

DISCUSSION...IN SPITE OF MIXED-LAYER CAPE VALUES GENERALLY IN THE
500 TO 1000 J/KG RANGE...THE TROPICAL ENVIRONMENT HAS PROVED TO BE
MORE THAN CAPABLE OF PRODUCING SUBSTANTIAL AMOUNTS OF RAIN IN
SHORT PERIODS OF TIME. MOST SOUNDINGS ACROSS THE MPD AREA HAVE
TYPICAL CHARACTERISTICS OF HEAVY RAINFALL SIGNATURES WITH
TALL/SKINNY INSTABILITY PROFILES AND UNIDIRECTIONAL
MID/UPPER-LEVEL FLOW. FURTHER...WET BULB ZERO HEIGHTS GENERALLY
RANGE FROM 13000 TO 14000 FT INDICATING THE IMPORTANCE OF WARM
RAIN PROCESSES HERE. IN A NOWCAST SENSE...SOUTHWESTERN PA AND
WESTERN DE ARE OF THE BIGGEST CONCERN. MESOSCALE CONVERGENCE ZONES
ARE EVIDENT IN THE LOW-LEVEL WIND FIELDS SUGGESTING THESE AREAS
MAY PERSIST FOR A WHILE LONGER.

IT HAS BEEN DIFFICULT TO RELY ON ANY ONE MESOSCALE MODEL SOLUTION
GIVEN THEIR POOR PERFORMANCE IN THIS REGIME. GIVEN THE ENVIRONMENT
IN PLACE...FUTURE INSTANCES OF SLOW-MOVING CONVECTION AND
POTENTIAL FLASH FLOODING ARE POSSIBLE AS LONG AS THESE CELLS
PERSIST. CONDITIONS SHOULD BECOME LESS FAVORABLE WELL BEYOND 00Z
GIVEN THE LOSS OF HEATING. ANY RESIDUAL INSTABILITY REMAINING
COULD PROVE TO KEEP CONVECTION GOING A BIT LONGER THOUGH.

RUBIN-OSTER

ATTN...WFO...AKQ...CTP...LWX...PBZ...PHI...RLX...

ATTN...RFC...MARFC...OHRFC...

LAT...LON   40967921 40517708 39957545 39287511 38747531
            38607573 38627618 39137734 39167821 38987883
            38887981 39228067 39938079 40808043


Last Updated: 503 PM EDT THU JUL 06 2017