MESOSCALE PRECIPITATION DISCUSSION 0454
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1152 PM EDT SAT JUL 14 2018

AREAS AFFECTED...SOUTHEAST MISSOURI...SOUTHERN ILLINOIS

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

VALID 150351Z - 150800Z

SUMMARY...SEVERAL WAVES OF RAIN AND THUNDERSTORMS MAY AFFECT
PORTIONS OF SOUTHERN MISSOURI AND ILLINOIS TONIGHT... AND THIS MAY
LEAD TO SOME FLASH FLOODING. RAIN RATES OF 2 IN/HR HAVE ALREADY
BEEN ESTIMATED BY RADAR... AND RAIN RATES THIS HIGH WILL BE A
POSSIBILITY INTO THE OVERNIGHT HOURS GIVEN THE ENVIRONMENT IN
PLACE.

DISCUSSION...KLSX RADAR SHOWED A WEAKENING SQUALL LINE PUSHING
EAST INTO SOUTH-CENTRAL ILLINOIS... NEAR THE I-57 CORRIDOR BY
0330Z. SURFACE OBSERVATIONS SHOWED A WEAK COLD POOL BEHIND THIS
WITH SURFACE TEMPERATURES AROUND 4-8 DEGREES COOLER THAN
OBSERVATIONS IN FAR SE IL AND SE MO. AN OUTFLOW BOUNDARY LIKELY
EXTENDED FROM NEAR CARBONDALE IL WEST TO NEAR ELLINGTON MO... AND
NEW CONVECTION WAS DEVELOPING IN THIS CORRIDOR. AN ADDITIONAL LINE
OF STORMS HAD DEVELOPED FURTHER WEST IN MISSOURI...AND WAS ALSO
ADVANCING INTO SOUTHEAST PORTIONS OF THE STATE. 850-300MB MEAN
FLOW WAS OUT OF THE WEST TO WEST-SOUTHWEST AND SHOULD ALLOW FOR
CONVECTION TO REPEATEDLY AFFECT SOME AREAS... WITH THE OUTFLOW
BOUNDARY POTENTIALLY PROVIDING AN ADDITIONAL FOCUSING MECHANISM.
THE HIGHEST QPE OVER THE PAST 6-12 HOURS WAS NEAR PERRYVILLE AND
FARMINGTON IN MISSOURI...AND STRETCHING NE/ENE INTO PARTS OF
SOUTH-CENTRAL ILLINOIS. GIVEN CURRENT STORM MOTIONS... THERE IS A
CHANCE THAT ADDITIONAL HEAVY RAINFALL WILL OCCUR IN SOME OF THESE
AREAS IN ADDITION TO SOME NEW SWATHS OF HEAVY RAINFALL FURTHER
SOUTH AND SOUTHWEST (NEAR THE CURRENT OUTFLOW BOUNDARY). THIS
WOULD PROVIDE SOME CHANCE OF FLASH FLOODING.

THE REGION DOES HAVE SOME ANOMALOUSLY HIGH MOISTURE LEVELS... WITH
PRECIPITABLE WATER VALUES NEAR OR JUST ABOVE 2 INCHES. THIS IS
ABOVE THE 95TH PERCENTILE FOR THIS REGION IN JULY... AND IS
SUFFICIENTLY HIGH TO SUPPORT EFFICIENT RAINFALL PRODUCTION AND
VERY HEAVY RAIN RATES AROUND 2 IN/HR IN THE STRONGEST CONVECTION.
RAP ANALYSIS ALSO SHOWED MLCAPE VALUES AROUND 2000-2500 J/KG ALONG
AND SOUTH OF THE AFOREMENTIONED OUTFLOW BOUNDARY WITH DEEP LAYER
EFFECTIVE SHEAR AROUND 20-25 KNOTS. THIS SHOULD ALLOW FOR
ORGANIZED CONVECTIVE CLUSTERS AND THE INCREASED STORM ORGANIZATION
COULD ENABLE INCREASED RESIDENCE TIME OF HEAVY RAIN IN A GIVEN
LOCATION.

LAMERS

ATTN...WFO...ILX...LSX...PAH...SGF...

ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...

LAT...LON   39038964 38668815 37768840 36788952 36839101
            37419191 38589157