MESOSCALE PRECIPITATION DISCUSSION 0280
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
204 AM EDT SUN JUN 10 2018

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

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

VALID 100603Z - 101100Z

SUMMARY...A WELL-ORGANIZED LINE OF STORMS WILL CONTINUE TO
PROGRESS EAST INTO PRIMARILY NORTHERN ILLINOIS IN THE PRE-DAWN
HOURS. VERY HEAVY RAIN RATES UP TO 2 IN/HR IN SPOTS MAY LEAD TO
FLASH FLOODING. ADDITIONALLY... SLOW MOVING HEAVY RAIN BANDS
APPEAR LIKELY NEAR THE WI-IL BORDER TO THE NORTH OF THE LINE OF
STORMS... AND THESE RAIN BANDS MAY ALSO PRODUCE LOCALLY HEAVY
RAINFALL AND FLOODING.

DISCUSSION...THE STORMS ACROSS EASTERN IOWA HAVE EVOLVED INTO A
WELL-ORGANIZED BOW ECHO...JUST CROSSING THE MISSISSIPPI RIVER
AROUND 06Z. THE NORTHERN END OF THE LINE HAS BEEN CONTINUALLY
ERODED OVER THE PAST FEW HOURS...LIKELY BY LOWER INSTABILITY ON
THE NORTHEAST SIDE OF THE CAPE GRADIENT THE BOW ECHO WAS
PROPAGATING ALONG. ALONG WITH NEW CELL GROWTH FURTHER SOUTH INTO
THE MORE UNSTABLE AIR MASS...THIS WAS LEADING TO AN EFFECTIVE ESE
OR SE MOTION FOR THE DOMINANT LINE SEGMENT WITH TIME. THE LINE
ALSO EXHIBITED A LONG TAIL TO THE WEST. AT 06Z THIS WAS SITUATED
FROM NEAR DAVENPORT IA TO NEAR IOWA CITY IA AND WEST ALONG I-80.

KDMX AND KDVN RADAR VWPS SHOWED THAT 850MB WINDS HAVE CONTINUED TO
VEER OVER THE PAST FEW HOURS AND ARE NOW WESTERLY. THE INFLOW
REGION WAS CHARACTERIZED BY MLCAPE VALUES OF AROUND 2000 J/KG WITH
PRECIPITABLE WATER VALUES AROUND 1.6 INCHES...AND THIS UNSTABLE
AND MOIST INFLOW WAS LIKELY CONTRIBUTING TO BACKBUILDING AND SOME
TRAINING WITH THIS TRAILING LINE OF CONVECTION. THIS SHOULD
CONTINUE FOR AT LEAST ANOTHER COUPLE HOURS...BUT THE EFFECT MAY
BEGIN TO DIMINISH AS THE OVERALL SQUALL LINE CONTINUES TO
PROPAGATE FURTHER AWAY FROM THE REGION OF STRONGEST INSTABILITY
OVER IOWA. NEVERTHELESS...THE TRAINING CONVECTION SHOULD PRODUCE
RAIN RATES TO AROUND 2 IN/HR (AS HAS BEEN SUGGESTED BY KDVN DUAL
POL ESTIMATES AND MRMS)...WHICH COULD LEAD TO AREAS OF FLASH
FLOODING. OTHER PORTIONS OF THE LINE MAY HAVE A SLIGHTLY LOWER
FLASH FLOOD RISK...BUT IT CANNOT BE RULED OUT GIVEN INHERENT
UNCERTAINTIES ABOUT CELL MERGERS AND THE BROAD PLUME OF 1.6 TO 1.7
INCH PWATS THAT THE LINE IS EMBEDDED IN.

FURTHER NORTH...RADAR LOOPS IMPLY A LOW-MID LEVEL CIRCULATION NEAR
GRANT COUNTY WI AND SURFACE OBSERVATIONS SHOW A WEAK CIRCULATION
AND LOCAL MINIMUM IN SURFACE PRESSURE IN THE SAME AREA. THIS IS
LIKELY ASSOCIATED WITH AN EARLIER MCV OR BOOKEND VORTEX ON THE
NORTH END OF THE LINE OF STORMS...WITH THE CONVECTION GENERALLY
DECAYING IN THE FEW HOURS SINCE. HOWEVER...THE CIRCULATION
APPEARED TO BE CONTRIBUTING TO ORGANIZED RAIN BANDS TO ITS
EAST...IN AN AREA OF LOW-LEVEL CONVERGENCE AND PERHAPS AN EAST TO
EAST-SOUTHEASTERLY WARM CONVEYOR BELT TO THE NORTH OF THE SYNOPTIC
SURFACE FRONT. THE RAIN BANDS IN THIS REGION APPEARED TO
OCCASIONALLY STALL AND HAVE ALREADY CONTRIBUTED TO LOCALIZED VERY
HEAVY RAIN RATES IN GRANT COUNTY WI. THIS MAY CONTINUE JUST TO THE
EAST FOR THE NEXT COUPLE HOURS. RADAR CROSS SECTIONS SHOW VERY
LIMITED REFLECTIVITY ABOVE THE MELTING LAYER OR -10C LAYER...SO
DOMINANT WARM RAIN PROCESSES COULD ENHANCE RAINFALL EFFICIENCY IN
THESE AREAS AND LEAD TO SOME LOCALIZED FLOODING AS WELL.

LAMERS

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

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

LAT...LON   43319023 42948879 42588740 41498712 40388790
            40478932 40789078 41199197 41759227 42019156
            42399103 43079125