MESOSCALE PRECIPITATION DISCUSSION 0619
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
505 PM EDT MON AUG 29 2016
 
AREAS AFFECTED...MUCH OF SOUTHERN AND EASTERN IA INTO NORTHERN IL 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 292105Z - 300100Z
 
SUMMARY...CONVECTION FORMING IN A HIGH MOISTURE ENVIRONMENT COULD
RESULT IN A FLASH FLOOD THREAT INTO THE EARLY EVENING HOURS. 

DISCUSSION...REGIONAL RADARS SHOWED THAT CONVECTION CONTINUES TO
SLOWLY FORM IN AN AXIS OF 2.00+ INCH PRECIPITABLE WATER AIR
STRETCHING ACROSS SOUTHERN IA INTO NORTHERN IL. RESIDUAL CIN HAS
BEEN ERASED...AND A RIBBON OF 1500-2500 J/KG MLCAPE IS ROUGHLY
COINCIDENT WITH THE MOISTURE AXIS. BOTH THE KLOT AND KDVN RADARS
SHOWED HOURLY RAINFALL RATES BETWEEN 1.50 AND 2.00 INCHES WITH
STORMS OVER NORTHERN IL. 

THE LATEST RAP SHOWED INSTABILITY REMAINING IN PLACE ACROSS
SOUTHERN IA AND NORTHERN IL THROUGH ABOUT 01Z...WHEN IS STARTS TO
WEAKEN. THE MOISTURE AXIS IS EXPECTED TO REMAIN IN PLACE AS
WELL...WITH PRECIPITABLE WATER VALUES REMAINING CLOSE TO 2.00
INCHES THROUGH THAT TIME. THE CONVECTION IS ALSO FORMING IN AN
AXIS OF LOWER ONE HOUR FLASH FLOOD GUIDANCE VALUES (GENERALLY
BETWEEN 1.00 AND 2.00 INCHES... WITH THE LOWEST VALUES ACROSS
NORTHERN IL.

WHILE WINDS ARE GENERALLY UNIDIRECTIONAL ACROSS THE REGION...WINDS
SPEEDS ARE FAIRLY WEAK (GENERALLY AROUND 10 KNOTS IN THE MID
LEVELS)...AND SLOW CELL MOTIONS ARE EXPECTED. THE BASIC
INGREDIENTS FOR A FLASH FLOOD THREAT ARE IN PLACE...BUT THERE IS
SOME CONCERN ABOUT THE EXTENT OF ADDITIONAL CONVECTIVE DEVELOPMENT
LATE THIS AFTERNOON (SINCE SYNOPTIC SCALE FORCING IS WEAK). THE
LATEST HRRR AND RAP HAVE BEGUN TO LATCH ONTO THE CURRENT
CONVECTION...AND BOTH KEEP ACTIVITY SCATTERED INTO THE EARLY
EVENING. 

GIVEN THE CURRENTLY HOURLY RAINFALL RATES...THE HRRR FORECAST OF
LOCAL 2.00 TO 3.00 INCHES OF RAINFALL SEEMS REASONABLE. GIVEN HOW
LOW FLASH FLOOD GUIDANCE VALUES ARE...THIS MUCH RAINFALL COULD
RESULT IN FLASH FLOODING. HOWEVER...SINCE THE EXTENT OF CONVECTION
IS IN NOT CERTAIN...FLASH FLOODING IS CONSIDERED POSSIBLE.

HAYES

ATTN...WFO...ARX...DMX...DVN...EAX...ILX...LOT...MKX...OAX...

ATTN...RFC...MBRFC...NCRFC...

LAT...LON   42899155 42618991 42448803 41938748 41538748 
            40928775 40518866 40339045 40579306 40659402 
            40659409 40799526 42359414 42869275