MESOSCALE PRECIPITATION DISCUSSION 0337
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 PM EDT WED JUN 20 2018

AREAS AFFECTED...SOUTHWEST PA...NORTHERN WV...WESTERN
MD...NORTHWEST VA...

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

VALID 201845Z - 202345Z

SUMMARY...INCREASING CONVECTIVE COVERAGE WITH TRAINING LINE
SEGMENTS OVER LOWER FFG VALUES.  FLASH FLOODING IS POSSIBLE
THROUGH EVENING HOURS.

DISCUSSION...GOES-16 VISIBLE IMAGERY SHOWS MULTIPLE LINES OF
DEVELOPING CONVECTION ACROSS SW PA AND ALONG THE OH/WV BORDER AS
WELL AS ALONG THE BLUE RIDGE RANGE IN VA.  A FRONTAL BOUNDARY
BISECTS OHIO ABOUT A THIRD OF THE WAY SOUTH TOWARD THE PIT METRO
BEFORE ANGLING SOUTH ACROSS WESTERN MD/EASTERN WV PANHANDLE INTO
THE POTOMAC RIVER VALLEY.  SHORTWAVE ENERGY ACROSS THE OHIO VALLEY
IS SUPPORTING MILD BROAD SCALE ASCENT COMBINED WITH RIGHT ENTRANCE
DYNAMICS WITH CONFLUENT JET ACROSS S PA INTO NJ ATTM.  COMBINED
WITH MODERATE BUOYANCY (1000-2000 J/KG) AND POOLED MOISTURE IN THE
RANGE OF 1.75-2" TPWS WILL SUPPORT SOLID RAINFALL EFFICIENCY WITH
RAIN RATES AOA 1.5"/HR.

CONCERN IS FOR CONVECTIVE CLUSTERS TO BECOME ORIENTED GENERALLY
WITH THE MEAN FLOW TO SUPPORT TRAINING CONVECTION AS INDIVIDUAL
CELLS ARE UNLIKELY TO HAVE THE DURATION FOR FLASH FLOODING ALONE. 
STRONGEST MOISTURE CONVERGENCE AND TRAINING IS MORE LIKELY FURTHER
NORTH ACROSS N WV OR SW PA GIVEN THE ORIENTATION OF THE FRONTAL
BOUNDARY...AS WAS THE CASE EARLIER WITH INITIAL ROUND OF
CONVECTION (THAT WAS JUST A SHADE BELOW FF THRESHOLDS NEAR 1-2")
IN SOMERSET/BEDFORD PA COUNTIES.  WITH STRONGER/BROADER UPDRAFTS
THIS EVENING ANY TRAINING TO THIS DURATION WOULD BE MORE LIKELY TO
PRODUCE FLASH FLOODING.  3HR FFG VALUES ARE IN THE RANGE OF 1.5-2"
ACROSS THE MAJORITY OF THE DISCUSSION AREA...AND ISOLATED TRACKS
EXCEEDING THESE VALUES ARE POSSIBLE THROUGH 00Z WITH NUMEROUS
HI-RES GUIDANCE SUPPORTING THIS IDEA WITH NO SPECIFIC AREA
HIGHLIGHTED OVER ANOTHER WITH EXCEPTION NEAR THE FRONTAL ZONE. 

GALLINA

ATTN...WFO...CTP...LWX...PBZ...RLX...

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

LAT...LON   40707984 40517826 39907730 38967796 37917869
            38488001 38648196 39688085 40178058 40678044