MESOSCALE PRECIPITATION DISCUSSION 0278...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
733 PM EDT SAT JUN 09 2018

CORRECTED FOR TYPOS

AREAS AFFECTED...PORTIONS OF VA & SOUTHERN MD

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

VALID 092329Z - 100229Z

SUMMARY...THUNDERSTORMS COULD CONTINUE TO POSE HEAVY RAIN ISSUES
FOR ANOTHER FEW HOURS ACROSS PORTIONS OF NORTHERN AND CENTRAL VA. 
HOURLY TOTALS TO 2" WITH LOCAL AMOUNTS TO 4" ARE POSSIBLE.

DISCUSSION...THUNDERSTORMS HAVE BEEN ATTEMPTING TO BROADEN IN
SCALE ACROSS NORTHERN AND EASTERN VA AS WELL AS SOUTHERN MD NEAR
AND EAST OF A MESOSCALE WAVE OF LOW PRESSURE, AHEAD OF A SHORTWAVE
MOVING ACROSS WV.  PRECIPITABLE WATER VALUES ARE ~1.75" PER RECENT
GPS DATA.  CONVERGENT 850 HPA FLOW HAS BEEN ROUGHLY OUT OF THE
WEST AT 15-20 KTS PER VAD WIND PROFILES.  THIS IS IMPORTING ML
CAPE VALUES OF 1500-2000 J/KG OUT OF CENTRAL AND NORTHERN VA
DOWNSTREAM TO THE EAST.  TO THE EAST OF THE WAVE, EFFECTIVE BULK
SHEAR OF 25 KTS IS ADVERTISED BY SPC MESOANALYSES.

THE 12Z HREF PROBABILITIES OF 1"+ AN HOUR SLOWLY FADE THROUGH 02Z
AS THUNDERSTORMS FROM THE NORTHWEST/BLUE RIDGE MOUNTAINS ATTEMPT
TO ERODE THE INSTABILITY POOL AND 850 HPA INFLOW WEAKENS, WHICH
WOULD COLLAPSE CONVECTION TO ITS EAST.  THE MESOSCALE GUIDANCE
ADVERTISES LOCAL AMOUNTS IN THE 2-3" RANGE OVER THE NEXT SEVERAL
HOURS, BUT STORMS NEAR THE NORTHERN NECK OF VA HAVE SHOWN GREATER
EFFICIENCY THAN WHAT HAS BEEN FORECAST AND SHOWS GREATER COVERAGE.
 CELL TRAINING APPEARS TO BE THE MAIN HEAVY RAINFALL THREAT. 
BELIEVE HOURLY RAIN TOTALS TO 2" WITH LOCAL AMOUNTS TO 4" ARE
REASONABLE OVER THE NEXT FEW HOURS BEFORE THE AIRMASS STABILIZES
AND THE STORMS FORWARD PROPAGATE AND SHIFT SOUTHEAST.  THIS HEAVY
RAIN IS EXPECTED TO FALL OVER PARTIALLY SATURATED SOILS.

ROTH

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

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

LAT...LON   39047798 38457638 37207568 37267741 37977894
            38837919