MESOSCALE PRECIPITATION DISCUSSION 0247
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
819 PM EDT THU MAY 31 2018

AREAS AFFECTED...EASTERN MD...CENTRAL AND VA

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

VALID 010020Z - 010320Z

SUMMARY...CELLS TRAINING ALONG A CONVECTIVE LINE IN A HIGH
MOISTURE ENVIRONMENT COULD PRODUCE HOURLY RAINFALL RATES NEAR 2.00
INCHES OVER PORTIONS OF EASTERN MD INTO CENTRAL VA. THIS COULD
PRODUCE FLASH FLOODING INTO THE EARLY MORNING HOURS.

DISCUSSION...REGIONAL RADARS INDICATED A NORTH/SOUTH LINE OF
CONVECTION CROSSING WESTERN VA INTO NORTHERN MD EARLY THIS
EVENING. WITHIN THE LINE...INDIVIDUAL CELLS ARE MOVING NORTHEAST
IN THE DEEP SOUTHWEST FLOW EXTENDING FROM THE SOUTHEAST STATES
INTO THE MID ATLANTIC. THE GOES-16 CLEAN IR LOOP SHOWED BURST OF
COLDER CLOUD TOPS ALONG THE LINE...WITH TEMPERATURES NEAR -65
CELSIUS WITH THE STRONGER CELLS.

ALONG AND AHEAD OF THE LINE...AN AREA OF 1500 J/KG OF MLCAPE CAPE
LIES ACOSS CENTRAL AND EASTERN VA INTO SOUTHERN MD. THE AXIS OF
INSTABILITY IS NEARLY COINCIDENT WITH AN AXIS OF 2.00/2.25 INCH
PRECIPITABLE WATER AIR (WHICH IS BETWEEN TWO AND THREE STANDARD
DEVIATIONS ABOVE THE MEAN). RAP MODEL SOUNDINGS SHOWED VERY HIGH
FREEZING LEVELS...ALONG WITH LONG THIN CAPE PROFILES. THESE ARE
INDICATIVE OF AN ENVIRONMENT THAT FOSTERS EFFICIENT RAINFALL IN
CONVECTION. IN THE AIRMASS...CONVECTIVE CELLS OVER MANASSAS AND
CULPEPPER VA HAS PRODUCED HOURLY RAINFALL RATES OVER 2.00 INCHES
AS THE ENTIRE LINE TRACKS TO THE EAST.

WEAK SHORT WAVE ENERGY OVER WV IS PROVIDING SUFFICIENT ASCENT FOR
CONVECTIVE ORGANIZATION. HOWEVER...THE SHORT WAVE IS PRODUCING
ENOUGH WESTERLY FLOW TO ALLOW THE LINE TO MOVE EASTWARD...WHICH IS
MITIGATING THE TRAINING THREAT TO SOME DEGREE. IN ADDITION...THERE
IS DISTINCT DRYING OCCUR WITH AND JUST AHEAD OF THE SHORT WAVE...
WHICH IS EXPECTED MOVE INTO WESTERN SECTIONS OF VA AFTER 01/03Z.

THE MOST RECENT HRRR (WHICH APPEARS TO LAGGING REALITY WITH
RESPECT TO THE MOVEMENT OF THE CONVECTION) SHOWED THE POTENTIAL
FOR LOCAL 2.00/3.00 INCH RAINFALL AMOUNTS WITH THE STORMS
EXTENDING FROM JUST EAST OF KDCA INTO CENTRAL VA. IN FACT...THE
31/23Z HRRR INDICATED LOCAL 4.00+ INCH RAINFALL AMOUNTS WEST OF
THE CHESAPEAKE BAY...THOUGH THE MOVEMENT OF THE LINE COULD MAKE
THOSE AMOUNTS TOO HIGH.

IN ANY EVENT...HIGHLY EFFICIENT CELLS TRAINING ALONG THE
CONVECTIVE LINE IS EXPECTED TO POSE A FLASH FLOOD THREAT INTO THE
EARLY MORNING HOURS.

HAYES

ATTN...WFO...AKQ...LWX...PHI...RNK...

ATTN...RFC...MARFC...SERFC...

LAT...LON   39337598 38777582 37297708 36977769 37247861
            38757727 39307635