MESOSCALE PRECIPITATION DISCUSSION 0274
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SAT JUN 09 2018

AREAS AFFECTED...SRN WISCONSIN...NRN ILLINOIS...FAR ERN IOWA

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

VALID 090659Z - 091230Z

SUMMARY...THUNDERSTORMS WERE BECOMING MORE NUMEROUS EARLY THIS
MORNING NEAR THE MISSISSIPPI RIVER TO THE NORTH OF THE QUAD
CITIES. THESE STORMS MAY PRODUCE LOCALIZED RAIN RATES TO AROUND 2
IN/HR WITH RAINFALL TOTALS TO AROUND 4 INCHES POSSIBLE. RAIN OF
THIS MAGNITUDE COULD LEAD TO FLASH FLOODING...PARTICULARLY OVER
URBAN AREAS.

DISCUSSION...REGIONAL RADARS SHOWED THAT CONVECTIVE COVERAGE HAD
BECOME MORE WIDESPREAD BETWEEN 05Z AND 07Z...WITH GOES-16 IR
CHANNELS SHOWING AN EXPANSION AND COOLING OF COLD CLOUD TOPS. THIS
WAS TAKING PLACE IN AN AREA OF DIFFLUENT UPPER LEVEL FLOW
IMMEDIATELY UPSTREAM OF A POTENT +PV ANOMALY IN NORTH-CENTRAL
ILLINOIS AROUND PONTIAC...VERY EVIDENT AS A SWIRL AND POCKET OF
DRIER AIR IN GOES-16 AIR MASS AND SIMPLE WATER VAPOR RGBS.
SATELLITE DERIVED WINDS FROM GOES-16 ALSO CLEARLY SHOW THE
DIFFLUENT FLOW PATTERN. ALSO LIKELY CONTRIBUTING TO THE BLOSSOMING
OF CONVECTION WAS INCREASING LOW-LEVEL MOISTURE TRANSPORT IN A
CORRIDOR FROM NERN MO TO NWRN IL...GENERALLY ASCENDING OVER A
LINGERING QUASI-STATIONARY FRONT AND A SHARPENING SECONDARY
BOUNDARY FROM NEAR CEDAR RAPIDS IA...TO NEAR PONTIAC IL (LIKELY
ENHANCED BY COOL FLOW OFF LAKE MICHIGAN).

DESPITE SOMEWHAT LIMITED INSTABILITY...RAP ANALYSIS DID SHOW
AROUND 500-1000 J/KG OF MUCAPE OVER MUCH OF THE OUTLINED
DISCUSSION AREA...AND STORMS ARE LIKELY BECOMING INCREASINGLY
ELEVATED - FORCED IN A LAYER AROUND 850MB NEAR THE NOSE OF THE
MOISTURE TRANSPORT MAXIMUM. THIS AMOUNT OF INSTABILITY WOULD BE
SUFFICIENT FOR THUNDERSTORMS TO REMAIN FAIRLY ORGANIZED AND
REALIZE RAIN RATES APPROACHING 2 IN/HR GIVEN THE PWATS AROUND 1.7
INCHES (PER GPS-PW OBSERVATIONS AND CIRA BLENDED TPW). THESE PWATS
ARE ALSO OVER THE 90TH PERCENTILE FOR EARLY-MID JUNE PER KDVN
SOUNDING CLIMATOLOGY AND CFSR REANALYSIS CLIMATOLOGY.

GIVEN THE WEAK FLOW IN THE VICINITY OF THE UPPER LEVEL PV
ANOMALY...STORM MOTIONS ARE BOTH SLOW AND SOMEWHAT CHAOTIC LEADING
TO CONSTRUCTIVE CELL INTERACTIONS. THESE WERE PROLONGING HEAVY
RAINFALL IN SOME AREAS...AND LEADING TO STALLING OR BACKBUILDING
IN SOME CASES (SUCH AS IN GRANT COUNTY WI AND ROCK ISLAND COUNTY
IL). COMPLEX CELL INTERACTIONS ARE LIKELY TO CONTINUE IN THIS
ENVIRONMENT...WHICH SHOULD LEAD TO LOCALIZED FLASH FLOODING ACROSS
THE REGION.

LAMERS

ATTN...WFO...ARX...DVN...LOT...MKX...

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

LAT...LON   43549063 43368945 42828758 41688729 41188837
            41659047 42429156 43169160