MESOSCALE PRECIPITATION DISCUSSION 0522
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
404 AM EDT FRI JUL 21 2017

AREAS AFFECTED...NRN IL INTO N-CNTRL IN

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

VALID 210802Z - 211300Z

SUMMARY...AN ISOLATED FLASH FLOOD THREAT WILL CONTINUE THROUGH
ABOUT 12Z FOR PORTIONS OF NRN IL INTO N-CNTRL IN. VERY HEAVY
RAINFALL RATES OF 1-2 IN/HR MAY CAUSE RUNOFF ISSUES WHERE TRAINING
DEVELOPS.

DISCUSSION...A COMBINATION OF EXPERIMENTAL GOES 16 INFRARED
IMAGERY AND REGIONAL RADAR IMAGERY SHOWED TWO CLUSTERS OF ESEWD
ADVANCING CONVECTION OVER THE IA/IL BORDER AND THE NRN IL/IN
BORDER. BOTH CLUSTERS APPEARED TO HAVE MCVS CONNECTED TO
THEM...WITH THE MCV ASSOCIATED WITH THE WESTERN CLUSTER OVER ERN
IA MORE DEFINED THAN THE MCV TIED TO THE ERN CLUSTER ACROSS NRN IL
AS OF 0730Z. HOWEVER...THE WRN CONVECTIVE CLUSTER APPEARS TO HAVE
SIGNIFICANTLY WEAKENED WITH ANY APPRECIABLE RAINFALL LIKELY
FINISHED FOR THE SHORT TERM. HOWEVER...THE ERN CONVECTIVE CLUSTER
CONTINUES TO EXPERIENCE COOLING OR STEADY-STATE CLOUD TOPS WHILE
ALSO FORWARD PROPAGATING TOWARD THE ESE. DESPITE WEAKENING TRENDS
IN INSTABILITY ACROSS THE REGION...THE SPC MESOANALYSIS PAGE
INDICATED 1500-2500 J/KG MUCAPE REMAINED AHEAD OF THE ERN
CONVECTIVE CLUSTER INTO N-CNTRL IN AS OF 07Z. LINGERING
INSTABILITY COMBINED WITH PRECIPITABLE WATER VALUES OF 1.8 TO 2.0
INCHES...PER RECENT GPS SITE VALUES...HAVE BEEN RESPONSIBLE FOR
RAINFALL OF 1 INCH OR MORE IN A 20-30 MINUTE PERIOD OVER N-CNTRL
IL PER WUNDERGROUND.COM OBSERVATION STATIONS.

THE ELEVATED CONVECTION WAS OCCURRING NORTH OF A SLOW MOVING FRONT
DRAPED WEST TO EAST ACROSS CNTRL IN/IL AT 07Z WITH RAP ANALYSIS
SOUNDINGS SUGGESTIVE THAT THE STORMS ARE ROOTED IN THE 850-700 MB
LAYER. STEERING FLOW IN THIS LAYER IS NEARLY IDENTICAL TO STORM
MOTIONS TOWARD THE ESE AT 20-30 KT. THE GREATEST FLASH FLOOD
THREAT OVER THE NEXT COUPLE OF HOURS APPEARS TO BE TIED TO THE SRN
FLANK OF THE ERN CONVECTIVE CLUSTER WHICH HAS BECOME ALIGNED
PARALLEL TO THE MEAN WIND SUGGESTING SHORT TERM TRAINING OF HEAVY
RAINFALL. ANY CELLS THAT DEVELOP OUT AHEAD OF THE FORWARD
PROPAGATING LINE MAY ALSO CAUSE A SHORT TERM TRAINING THREAT.

DESPITE WANING INSTABILITY...A LOW RISK OF FLASH FLOODING WILL
EXIST WITH THIS SYSTEM WITH LOCALIZED 2-3 INCH TOTALS POSSIBLE
THROUGH 13Z...WHICH MAY OCCUR VERY QUICKLY LEADING TO A FEW RUNOFF
ISSUES.

OTTO

ATTN...WFO...DVN...ILN...ILX...IND...IWX...LOT...

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

LAT...LON   41408827 41378725 40838539 40608476 39988391
            39528433 39438537 39578714 40418863 40728935
            41108926