MESOSCALE PRECIPITATION DISCUSSION 0491
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
209 PM EDT FRI JUL 20 2018

AREAS AFFECTED...SOUTHEAST IN...NORTHERN KY...WEST-CENTRAL TO
SOUTHWEST OH

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

VALID 201805Z - 210005Z

SUMMARY...VERY HEAVY SHOWERS AND THUNDERSTORMS CAN BE EXPECTED
THROUGH THE AFTERNOON AND EARLY EVENING HOURS. FLASH FLOODING WILL
BE LIKELY AND ESPECIALLY NEAR AREAS THAT SAW EARLIER HEAVY RAINS.

DISCUSSION...THE LATEST SYNOPTIC PATTERN FEATURES AN AMPLIFYING
UPPER TROUGH AND ASSOCIATED CLOSED LOW DROPPING SLOWLY SOUTHEAST
TOWARD THE LOWER OH VALLEY. ALREADY THERE IS AN EXPANSIVE AREA OF
COLD-TOPPED CONVECTION IMPACTING PORTIONS OF WEST-CENTRAL AND
SOUTHWEST OH IN RESPONSE TO STRONG WARM AIR ADVECTION AHEAD OF A
COLD FRONT AND A VERY MOIST/UNSTABLE AIRMASS AHEAD OF IT WHICH IS
OVERRUNNING A WARM FRONT ATTEMPTING TO LIFT NORTHEAST ACROSS
WESTERN OH.

THE LATEST AREA VWP DATA SHOWS A SOUTHWEST LOW LEVEL JET OF ABOUT
30 KTS AHEAD OF THE COLD FRONT...ALONG WITH A NOSE OF STRONG
INSTABILITY CHARACTERIZED BY MLCAPE VALUE OF 3000 TO 4000 J/KG.
MEANWHILE...PWATS ARE RUNNING BETWEEN 1.5 AND 1.75 INCHES...WITH
THE LOW LEVELS IN PARTICULAR QUITE MOIST AS SEEN WITH SURFACE
DEWPOINTS IN THE MID 70S WITHIN THE WARM SECTOR.

OVER THE NEXT FEW HOURS...THE CONVECTION ONGOING OVER WEST-CENTRAL
TO SOUTHWEST OH SHOULD TEND TO BECOME A BIT MORE CONCENTRATED AND
WILL ALSO EXPAND MORE TO THE SOUTHWEST INCLUDING AREAS OF NORTHERN
KY AND SOUTHEAST IN AS STRONG DIURNAL HEATING FOSTERS ADDITIONAL
ENHANCEMENT OF SURFACE-BASED INSTABILITY. MEANWHILE...INCREASINGLY
STRONG 250 MB LEFT-EXIT REGION JET DYNAMICS WILL BE ARRIVING IN
ASSOCIATION WITH THE DIGGING UPPER TROUGH WHICH WILL BEGIN TO TAKE
ON A NEGATIVE TILT.

LOCALLY VERY HEAVY RAINS CAN BE EXPECTED WITH RAINFALL RATES OF AS
MUCH AS 2.5 INCHES/HR. THE LATEST HIRES CAM GUIDANCE AND
ESPECIALLY THE HRRR DOES NOT HAVE TOO GOOD OF A HANDLE ON THE
ACTIVITY FOCUSING OVER WEST-CENTRAL OH...BUT IS A BIT BETTER OVER
SOUTHEAST IN. EXPECT AS MUCH AS 3 TO 4 INCHES OF RAIN THROUGH 00Z
WITH THE EXPECTED UPTICK IN CONVECTIVE COVERAGE AND
ORGANIZATION...AND THIS WILL LIKELY CAUSE SOME FLASH FLOODING.
THIS WILL ESPECIALLY BE THE CASE OVER AREAS THAT SAW HEAVIER RAINS
EARLIER THIS MORNING.

ORRISON

ATTN...WFO...CLE...ILN...IND...JKL...LMK...PAH...RLX...

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

LAT...LON   40628339 40108286 39228265 38568314 38148400
            37768535 37638619 37718653 38108678 38468671
            38888638 39218593 39708518 40618431