MESOSCALE PRECIPITATION DISCUSSION 0712
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 PM EDT TUE AUG 22 2017

AREAS AFFECTED...WV...WESTERN PA...FAR WESTERN NY STATE

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

VALID 221910Z - 222310Z

SUMMARY...LINES OF MAINLY PRE FRONTAL CONVECTION COULD TRAIN OVER
AREAS WITH LOWER ONE HOUR FLASH FLOOD GUIDANCE VALUES...RESULTING
IN A FLASH FLOOD THREAT INTO THE LATE AFTERNOON HOURS.

DISCUSSION...REGIONAL RADARS SHOWED LINES OF PRE FRONTAL
CONVECTION OVER OH... NORTHERN KY INTO WESTERN PA THIS AFTERNOON.
THE CONVECTION IS FIRING ON AN AXIS OF 1000-2000 J/KG OF MLCAPE
STRETCHING FROM THE TN VALLEY INTO WESTERN AND CENTRAL PA. A
RIBBON OF 1.50/1.75 INCH PRECIPITABLE WATER EXTENDS ALONG ROUGHLY
THE SAME AXIS.

THE CONVECTIVE MODE IS CURRENTLY OUTFLOW DOMINATED...BASED ON THE
RADAR PRESENTATION AND DRY AIR IN THE MID LEVELS (PER RAP
SOUNDINGS OVER OH INTO NORTHERN KY). THE MOST RECENT HRRR AND RAP
SUGGEST THIS MODE CONTINUES INTO THE LATE AFTERNOON HOURS... AS
PROPAGATION VECTORS SUGGEST A SOUTHWEST TO NORTHWEST STORM TRACK.

THE MAIN CONCERN FOR FLASH FLOODING IS TIED TO THE POTENTIAL FOR
TRAINING. AS LINES OF CONVECTION TRACK OVER THE SAME LOCATIONS IN
NORTHERN WV...WESTERN PA INTO FAR WESTERN NY STATE...THEY WILL
PRODUCE HEAVY RAINFALL OVER AREAS WITH ONE HOUR FLASH FLOOD
GUIDANCE VALUES BETWEEN 1.00 AND 1.50 INCHES.

MOST OF THE AVAILABLE HIGH RESOLUTION GUIDANCE IS NOT CAPTURING
THE PRE FRONTAL CONVECTION WELL (OR AT ALL IN SOME
CASES)...INSTEAD FOCUSING ON WHERE THESE SOLUTIONS PLACE THE
FRONTAL BASED STORMS. BECAUSE OF THAT...THE HIGH RESOLUTION MODELS
APPEAR TO BE 2-3 HOURS SLOW.

HOWEVER...THE LATEST HRRR AMOUNTS SHOWING 1.00 TO 2.00 INCHES OF
RAINFALL WITH MAINLY PROGRESSIVE CONVECTION SEEMS REASONABLE.
AMOUNTS THIS HIGH COULD PRODUCE FLASH FLOODING IN AREAS WITH LOWER
FLASH FLOOD GUIDANCE VALUES INTO THE LATE AFTERNOON HOURS.

HAYES

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

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

LAT...LON   43387854 43357760 42267729 39047868 37938009
            38168217 38188217 38558229 39578160 41538059
            42327978