MESOSCALE PRECIPITATION DISCUSSION 0169
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 PM EDT MON MAY 02 2016
 
AREAS AFFECTED...PORTIONS OF THE CNTRL APPALACHIANS TOWARD THE DC
METRO 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 021844Z - 030030Z
 
SUMMARY...SCATTERED THUNDERSTORMS WITH RAINFALL RATES UP TO 1.5
IN/HR WILL POSE A FLASH FLOOD THREAT ACROSS PARTS OF THE CENTRAL
APPALACHIANS...EWD TOWARD THE DC METRO THROUGH THIS EVENING. LOW
FLASH FLOOD GUIDANCE IS THE MAIN REASON FOR THE THREAT.

DISCUSSION...18Z OBSERVATIONS PLACED A COLD FRONT ACROSS THE
N-CNTRL APPALACHIANS EXTENDING ENE TO WSW WITH A WEAK SURFACE LOW
NEAR THE OHIO/KENTUCKY BORDER. SURFACE DEWPOINTS ARE IN THE UPPER
50S TO LOWER 60S ACROSS ERN KENTUCKY INTO SRN WEST VIRGINIA AND
WRN VIRGINIA. THESE VALUES HAVE ALLOWED FOR PRECIPITABLE WATER
VALUES TO GET INTO THE 1.25 TO 1.50 INCH RANGE VIA RECENT GPS SITE
MEASUREMENTS IN ERN KENTUCKY AT 1645Z...ALONG WITH WEAK MLCAPE OF
500 - 1000+ J/KG WHICH IS HIGHER TO THE SOUTH AND WEST GIVEN SOLAR
INSOLATION. REGIONAL RADAR IMAGERY HAS SHOWN INCREASING
THUNDERSTORM COVERAGE OF CELLS AHEAD OF A MORE WIDESPREAD RAINFALL
CLUSTER MOVING EAST ACROSS CNTRL KENTUCKY/TENNESSEE. A REMNANT MCV
WAS ALSO VISIBLE OVER W-CNTRL TENNESSEE AT 1830Z...MOVING NEWD
WITH LOCALLY STRONGER 850-700 MB FLOW OUT AHEAD HELPING TO
INCREASE CONVECTIVE COVERAGE OUT AHEAD IN E-CNTRL TENNESSEE.

GIVEN RECENT RAINFALL AND MOUNTAINOUS TERRAIN...FLASH FLOOD
GUIDANCE ACROSS MUCH OF THE MPD THREAT AREA IS ONLY 0.50 TO 1.00
IN/HR. FLOW IS UNIDIRECTIONAL FROM FROM THE WSW...WHICH MAY ALLOW
FOR BRIEF PERIODS OF TRAINING HEAVY RAINFALL. WHILE PRESENT CAPE
VALUES ARE LOWER ACROSS NRN SECTIONS OF THE MPD THREAT
AREA...INCREASING LOW LEVEL MOISTURE AND MOSTLY CLEAR SKIES MAY
ALLOW FOR INSTABILITY TO REACH ABOVE 1000 J/KG AND SUPPORT
RAINFALL RATES IN EXCESS OF FLASH FLOOD GUIDANCE. GIVEN FORCING IS
LESS CLEAR EAST OF THE APPALACHIANS...CONFIDENCE IS A BIT LOWER IN
THE COVERAGE OF HEAVY RAINFALL...BUT SOME OF THE 12Z HI-RES
GUIDANCE SUPPORTS THE FLASH FLOOD POTENTIAL HERE.

OTTO

ATTN...WFO...AKQ...JKL...LWX...MRX...PBZ...RLX...RNK...

ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...

LAT...LON   39457934 39457789 39357715 39177683 38867694 
            38407773 37787842 37617874 37517952 37337983 
            36988094 36888193 36958288 37418310 37918299 
            38268250 38808162