MESOSCALE PRECIPITATION DISCUSSION 0494
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
555 PM EDT FRI JUL 20 2018

AREAS AFFECTED...SOUTHERN/EASTERN IN...CENTRAL/EASTERN
KY...SOUTHWEST TO SOUTH-CENTRAL OH...WEST-CENTRAL WV

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

VALID 202155Z - 210330Z

SUMMARY...HEAVY RAINFALL AND RESULTANT FLASH FLOODING WILL REMAIN
LIKELY GOING INTO THE EVENING HOURS AS SHOWERS AND THUNDERSTORMS
CONTINUE ORGANIZE.

DISCUSSION...THE LATE-AFTERNOON GOES-16 1-MINUTE VISIBLE SATELLITE
IMAGERY SUGGESTS A VERY UNSTABLE BOUNDARY LAYER ACROSS MUCH OF
SOUTHERN IN AND CENTRAL/SOUTHERN KY GIVEN NUMEROUS LOW LEVEL CLOUD
STREETS THAT ARE SEEN ALIGNED WITH THE MOIST WARM SECTOR SOUTHERLY
FLOW PATTERN. THIS UNSTABLE WARM SECTOR IS STRONGLY SUSTAINING A
RATHER WELL-ORGANIZED MCS THAT IS IMPACTING FAR SOUTHERN OH AND
STRETCHING DOWN ACROSS NORTH-CENTRAL/NORTHEAST KY AND FOCUSED NEAR
A WARM FRONT ATTEMPTING TO LIFT NORTHEAST TOWARD THE UPPER OH
VALLEY.

OVER THE NEXT SEVERAL HOURS...THE CONVECTION SHOULD REMAIN QUITE
ORGANIZED AND IS EXPECTED TO CONTINUE TO FOCUS DOWN TO THE
EAST-SOUTHEAST WITH IMPACTS ON PARTS OF SOUTHEAST KY AND INTO
WEST-CENTRAL WV. THE UPSTREAM ENVIRONMENT THOUGH OVER WESTERN KY
AND SOUTHEAST IN IS QUITE UNSTABLE AS WELL WHICH IS FOCUSED OUT
AHEAD OF A COLD FRONT THAT IS ASSOCIATED WITH THE AMPLIFYING AND
NEGATIVELY TILTING UPPER TROUGH OVER THE MIDWEST. THE CONCERN
MOVING INTO THE EVENING HOURS IS THAT NEW CONVECTION MAY REDEVELOP
ALONG OR NEAR THE WESTERN FLANK OF THE CURRENT CONVECTIVE COLD
POOL AND POTENTIALLY BACKBUILD AND REPEAT OVER THE SAME AREA GIVEN
THE VERY MOIST/UNSTABLE AND CONVERGENT SOUTHWEST LOW LEVEL INFLOW.
ADDITIONALLY...THERE ARE FAVORABLE SHEAR PARAMETERS AND FORCING
ASSOCIATED WITH 250 MB LEFT-EXIT REGION JET DYNAMICS THAT COUPLED
WITH SUCH STRONG BOUNDARY LAYER INSTABILITY SHOULD SUPPORT
ADDITIONAL CLUSTERS OF ORGANIZED CONVECTION OVER THE BROADER UPPER
OH VALLEY OVER THE NEXT FEW HOURS. THIS WILL INCLUDE
SOUTHERN/EASTERN IN AND PORTIONS OF WESTERN OH WHERE NEW
CONVECTIVE DEVELOPMENT IS CURRENTLY BEING NOTICED.

EXPECT RAINFALL RATES TO BE AS HIGH AS 2.5 INCHES/HR GIVEN THE
HIGH PWAT ENVIRONMENT AND STRONG CONVECTIVE FORCING. THE LATEST
HIRES MODEL CONSENSUS FAVORS AS MUCH AS AN ADDITIONAL 3 TO 4
INCHES OF RAIN THROUGH 03Z...AND THIS WILL LIKELY RESULT IN MORE
AREAS OF FLASH FLOODING. THE MORE PRONE AREAS WILL BE LOCATIONS
THAT SAW HEAVY RAIN EARLIER TODAY WHERE SOIL CONDITIONS HAVE NOW
BECOME VERY MOIST AND LOCALLY SATURATED.

ORRISON

ATTN...WFO...ILN...IND...IWX...JKL...LMK...RLX...

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

LAT...LON   40898511 40798438 40158409 39648332 39198227
            38228202 37468250 37118309 36828409 36728534
            36998608 37658665 38468669 39018639 39678588