MESOSCALE PRECIPITATION DISCUSSION 0369
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
530 PM EDT WED JUN 27 2018

AREAS AFFECTED...NORTHERN WV INTO CENTRAL PA

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

VALID 272130Z - 230330Z

SUMMARY...CONVECTION TRACKING OVER AREAS WITH LOWER FLASH FLOOD
GUIDANCE VALUES COULD POSE A FLASH FLOOD THREAT THROUGH THE LATE
EVENING HOURS.

DISCUSSION...REGIONAL RADARS ACROSS EASTERN OH/WV INTO WESTERN PA
INDICATED AN INCREASE IN CONVECTIVE COVERAGE...AS LOW LEVEL CIN IS
ERODED NEAR AND WEST OF A WARM FRONT EXTENDING THROUGH THE REGION.
THE CONVECTION IS TAPPING 1000-1500 J/KG OF MUCAPE LOCATED OVER
SOUTHERN OH AND WESTERN WV. SHORT WAVE ENERGY APPROACHING FROM THE
GREAT LAKES IS EXPECTED TO PROVIDE SUFFICIENT SYNOPTIC SCALE
ASCENT TO ALLOW THE CONVECTIVE COVERAGE TO INCREASE FURTHER INTO
THE EARLY EVENING.

THE CONVECTION IS FORMING IN AN AXIS OF 1.50/1.75 INCH
PRECIPITABLE WATER AIR...AND THE HIGH MOISTURE CONTENT AIRMASS IS
ALREADY LEADING TO HOURLY RAINFALL RATES BETWEEN 1.00/1.25 INCHES
OVER PORTIONS OF NORTHERN WV (PER THE KRLX RADAR). RAINFALL RATES
THIS HIGH COULD POSE A FLASH FLOOD RISK IN PLACES LIKE NORTHERN WV
AND NEARBY WESTERN VA IN THE NEAR TERM...WHERE ONE AND THREE HOUR
FLASH FLOOD NUMBERS ARE AS LOW AS AN INCH.

AS THE WARM FRONT MOVES NORTHEAST ACROSS WV/WESTERN WV INTO
CENTRAL PA DURING THE EVENING...A 25/35 KNOT CONVERGENT LOW LEVEL
FLOW BEGINS TAPPING DEEPER MOISTURE FROM A STREAM OF 1.75/2.00
INCH PRECIPITABLE WATER AIR LYING ACROSS EASTERN VA DURING THE
EARLY EVENING. THE DEEPER MOISTURE... COUPLED WITH INCREASING
INSTABILITY (AS MUCAPE VALUES RISE TO BETWEEN 500-1000 J/KG OVER
CENTRAL PA NEAR AND BEHIND THE WARM FRONT)...SHOULD ALLOW
CONVECTION TO PRODUCE HOURLY RAINFALL RATES NEARING 1.50 INCHES
OVER PORTIONS OF CENTRAL PA AFTER 28/23Z.

AFTER THAT TIME...THE MAIN FLASH FLOOD THREAT COULD SHIFT INTO
CENTRAL PA...WHERE THE LATEST HRRR/EXPERIMENTAL HRRR INDICATED
LOCAL RAINFALL AMOUNTS BETWEEN 2.00/3.00 INCHES. INCREASING
DIVERGENCE AHEAD OF THE SHORT WAVE COULD ALLOW THE CONVECTION TO
EXPAND IN COVERAGE...EVEN AFTER 28/03Z. AT THIS POINT...BECAUSE
THE OVERALL COVERAGE IS STILL IN QUESTION...FLASH FLOODING IS
CONSIDERED POSSIBLY INTO THE EVENING.

HAYES

ATTN...WFO...BGM...CTP...LWX...PBZ...RLX...RNK...

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

LAT...LON   41737669 40787632 39597742 38697792 38307825
            38097891 38157967 38628103 39748068 40797950
            41507808