MESOSCALE PRECIPITATION DISCUSSION 0586
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
445 PM EDT FRI JUL 28 2017

AREAS AFFECTED...EASTERN OH...SOUTHERN PA...NORTHERN WV...NORTHERN
VA...MD...DE

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 282045Z - 290300Z

SUMMARY...VERY STRONG DYNAMIC ENVIRONMENT WITH DEEP MOISTURE WILL
SUPPORT SIGNIFICANT FLASH FLOODING/FLOODING THROUGH THIS EVENING
ALONG DEFORMATION ZONE WITH LARGE AREA OF AREAL TOTALS OF 2-4"
WITH LOCALIZED TOTALS OF 6-7" POSSIBLE LEADING TO LIFE-THREATENING
FLOODING. 

DISCUSSION...GOES-E WV LOOP SHOWS VERY STRONG COMPACT CLOSED LOW
DEVELOPING OVER SE MI DIGGING SOUTHEAST RAPIDLY EXPANDING THE
DIFFLUENT AREA OF THE LEFT EXIT REGION OF UNSEASONABLY STRONG
80-90KT 3H JET ACROSS THE MIDWEST.  THIS IS SUPPORTING A
DEVELOPING CYCLONE OVER N WV ATTM WITH CLOSING LOWS VERTICALLY
TILTING BACK TOWARD THE NW...THIS SHOULD STRONGLY SUPPORT VERY
STRONG WARM CONVEYOR ACROSS THE CAROLINAS/S MID-ATLANTIC TO ASCEND
ACROSS DEVELOPING TROWAL/DEFORMATION ZONE ACROSS SW PA TOWARD THE
DELMARVA CURRENTLY.

WARM CONVEYOR OVER E VA TO THE DELMARVA IS REPRESENTED BY
2000-2500 J/KG OF MLCAPE AND STRONG MOISTURE FLUX TO ALLOW FOR
TPWS IN EXCESS OF 2.2" WITH STRONG CONVERGENCE DEEP CONVECTION CAN
BE SEEN ALONG THE INTERFACE WITH THE DEFORMATION ZONE WITH TOPS TO
-65C ALLOWING FOR RAIN RATES OF 2.5"/HR FROM SE MD TO S DE.  IN
PROXIMITY TO THE DEEPENING LOW/ISALLOBARIC INFLUENCE AND
DEFORMATION ZONE...CELLS ARE NEARLY STATIONARY.  ADDITIONALLY
SLANTWISE INSTABILITY WITH MUCAPES TO 2000 J/KG (PER SPECIAL 18Z
IAD SOUNDING) WILL SUPPORT THE POTENTIAL FOR ELEVATED CONVECTIVE
ELEMENTS THROUGH CENTRAL MD AND SE PA AS WELL.  EVEN WITHOUT DEEP
CONVECTION...BROAD SCALE ASCENT IN THE TROWAL AND DEEP MOISTURE
SHOULD SUPPORT MODEST RAINFALL AT BEST LEADING TO COMPOUNDING
TOTALS FOR INUNDATION FLOODING OVER A BROADER AREA WITH LOCALIZED
FLASH FLOODING POCKETS WHERE THE CONVECTIVE ELEMENTS ARE.  BROAD
AREA OF 2-4" OF RAIN IS EXPECTED WITH ISOLATED TOTALS OF 6-7"
POSSIBLE THROUGH 03Z (ESPECIALLY OVER SE MD/DELMARVA) ARE LIKELY
TO POSE LIFE-THREATENING RISK FOR FLOODING. 

FURTHER NORTHWEST E OH/N WV/SW PA... CLEARING SKIES OF E OH/SW PA
TO REACH 1500/2000 J/KG WITH NARROW SKINNY PROFILES.  THIS ALONG
WITH STRONG LOW TO MID-LEVEL FRONTOGENESIS ASCENT SUPPORTS THE
CAPABILITY OF CONTINUED HIGH RATES AND GIVEN HIGH DEFORAMTIONAL
ZONE/STRETCHING BETWEEN THE SURFACE/5H LOW...CELL MOTIONS ARE
NEARLY ZERO ALLOWING FOR COMPOUNDING RAINFALL TOTALS.  GIVEN
SLIGHTLY LOWER MOISTURE AVAILABILITY RATES OF 1.75-2"/HR ARE
LIKELY WITH A MODEST AREAL COVERAGE OF 2-3" POSSIBLE WITH ISOLATED
POCKETS OF 5"+ WITHIN COMPLEX TERRAIN POSES LIFE THREATENING FLASH
FLOOD CAPABILITIES THROUGH THE LATE EVENING/EARLY OVERNIGHT ACROSS
S/SW PA/N WV/W MD PANHANDLE.

GALLINA

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

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

LAT...LON   40707986 40657811 40287565 39657507 39037478
            38667479 38037503 37607522 37457548 37867670
            38257882 39188116 39858160 40648094