MESOSCALE PRECIPITATION DISCUSSION 0117
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
101 AM EDT SAT JUN 22 2013
 
AREAS AFFECTED...FAR EASTERN IA...SOUTHERN WI...NORTHERN IL 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 220501Z - 220731Z
 
SUMMARY...AN EAST-WEST BAND OF CONVECTION IN SOUTHERN WI IS
EXPECTED TO SHIFT SLOWLY SOUTHWARD TOWARDS NORTHERN IL. 
CONSIDERING THE SATURATED SOILS IN THE AREA FROM RECENT RAINS,
FLASH FLOODING IS POSSIBLE.

DISCUSSION...A LOW-LEVEL JET -- AT 850 HPA -- OF 40 KNOTS IS
OVERRIDING A WEAK POLAR FRONT/BAROCLINIC TROUGH AND HAS LED TO THE
DEVELOPMENT OF AN EAST-WEST BAND OF THUNDERSTORMS ACROSS SOUTHERN
WI WHICH HAS SOLIDIFIED AS OF LATE WITHIN AN AXIS OF HIGH
MOISTURE.  THE MEAN FLOW IS PARALLEL TO THE 850 HPA WIND PATTERN,
WHICH HAS LED TO THIS BAND.  PRECIPITABLE WATER VALUES OF 1.75-2
INCHES ARE AIDING PRECIPITATION EFFICIENCY OF THE THUNDERSTORMS. 
THE REGION HAS DIVERGENCE ALOFT EAST OF AN UPPER LOW MOVING ACROSS
ID.  THIS BAND SHOULD SHIFT SLOWLY SOUTHWARD OVER THE NEXT FEW
HOURS INTO NORTHERN IL AS THE LOW-LEVEL INFLOW SHIFTS IN TANDEM. 
INFLOW AT THE 850 HPA LEVEL INTO THE REGION IS EXPECTED TO WEAKEN
SOMEWHAT AS TIME GOES ON, WHICH SHOULD REDUCE THE REGIONAL THREAT
FOR FLASH FLOODING, HENCE THE POSSIBLE WORDING.  CONSIDERING THAT
FLASH FLOOD GUIDANCE VALUES ARE RATHER LOW -- 1.5 INCHES/3 HOURS
-- DUE TO RECENT RAINS, THINK FLASH FLOODING WILL BE POSSIBLE IN
THIS REGION AS LOCAL RAINFALL AMOUNTS OF 2-3 INCHES ARE EXPECTED
OVER THE NEXT COUPLE HOURS.  THE INTENT IS TO MERGE THIS AREA IN
WITH THE LARGER HEAVY RAIN EVENT TO THE WEST NEAR THE NE/SD/MN/IA
BORDER AREA LATER TONIGHT/EARLY SATURDAY MORNING, WHICH LED TO A
SHORT DURATION FOR THIS MESOSCALE PRECIPITATION DISCUSSION.

ROTH

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

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

LAT...LON   42018751 41688896 41779082 42159208 42889184 43219089
            43288888 42938753 42018751