MESOSCALE PRECIPITATION DISCUSSION 0393
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
128 PM EDT TUE JUL 03 2018

AREAS AFFECTED...WRN/CTRL KY...SRN IN...SWRN OH...SERN IL...NRN TN

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 031727Z - 032327Z

SUMMARY...SLOW-MOVING THUNDERSTORMS WILL BUILD DURING THE
AFTERNOON HOURS ACROSS THE LOWER OHIO RIVER VALLEY AND MAY LEAD TO
LOCALIZED FLASH FLOODING OVER MUCH OF THE REGION.
THEREFORE...ALTHOUGH WIDESPREAD FLOODING IS NOT ANTICIPATED...A
SCATTERING OF FLOODING ISSUES IS EXPECTED. RAIN RATES MAY REACH
1.5 TO 2.0 IN/HR IN SOME AREAS.

DISCUSSION...REGIONAL RADARS AND GOES-16 VISIBLE AND IR SATELLITE
IMAGERY SHOWED SCATTERED CONVECTION BECOMING MORE NUMEROUS ACROSS
THE LOWER OHIO RIVER VALLEY BETWEEN 16-17Z. STORM MOTIONS WERE
RATHER SLOW...WHICH IS EXPECTED TO CONTINUE GIVEN THE PROXIMITY TO
THE MID-UPPER LEVEL RIDGE AXIS (AND ASSOCIATED WEAK FLOW). IN
GENERAL...MOST CELLS WERE MOVING AROUND 10-15 KNOTS WITH SOME
BACKBUILDING AND STALLING ALSO NOTED IN AREAS OF CELL MERGERS. THE
SLOW STORM MOTIONS WILL EXACERBATE THE HEAVY RAINFALL THREAT. AN
ADDITIONAL CONSIDERATION IS THE DEEP MOISTURE AVAILABLE WITH A PW
AXIS OF 2+ INCH VALUES SITUATED JUST SOUTH OF THE OHIO RIVER AS OF
17Z (PER RAP ANALYSIS AND CIRA BLENDED PWS). A GPS-PW OBSERVATION
IN WEST-CENTRAL KENTUCKY WAS REPORTING A VALUE OF 2.13 INCHES.
SUCH VALUES WERE ABOVE THE 99TH PERCENTILE BASED ON CSFR
CLIMATOLOGY FOR THIS REGION...AND WOULD BE SUPPORTIVE OF VERY
HEAVY RAIN RATES. MOST HI-RES MODELS SHOW CONVECTIVE MODE
REMAINING SINGLE-CELL (AND RELATIVELY SCATTERED) BUT SOME STORM
MERGERS MAY PRODUCE SMALL CLUSTERS AND ENABLE HEAVY RAINFALL TO
LINGER IN LOCALIZED AREAS FOR A COUPLE HOURS. ANTECEDENT
CONDITIONS ARE ALSO FAVORABLE FOR FLASH FLOODING WITH 14-DAY
RAINFALL ABOVE 200 PERCENT OF NORMAL IN MUCH OF THE REGION. ALL
THESE FACTORS ARE FAVORABLE FOR FLASH FLOODING. THE EXPECTATION IS
THAT FLOODING WILL REMAIN SOMEWHAT LOCALIZED GIVEN THE SCATTERED
NATURE OF CONVECTION...BUT THAT FLOODING IS MORE LIKELY THAN
NORMAL PARTICULARLY GIVEN THE ANOMALOUSLY HIGH MOISTURE LEVELS AND
ANTECEDENT CONDITIONS.

LAMERS

ATTN...WFO...ILN...IND...JKL...LMK...OHX...PAH...

ATTN...RFC...LMRFC...OHRFC...

LAT...LON   39598606 39538397 37938410 36618529 36028660
            36548798 37998832