MESOSCALE PRECIPITATION DISCUSSION 0041
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
525 AM EDT FRI MAY 17 2013
 
AREAS AFFECTED...EASTERN IA/MN BORDER AND SOUTHERN WI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 170920Z - 171320Z
 
SUMMARY...HEAVY RAINFALL AND RESULTANT FLASH FLOODING IS POSSIBLE
FROM THE EASTERN MN/IA BORDER INTO SOUTHERN WISCONSIN OVER THE
NEXT SEVERAL HOURS.

DISCUSSION...LOW-LEVEL INFLOW IS BEING DIRECTED INTO A FRONTAL
BOUNDARY AT THE 850 HPA LEVEL AHEAD OF AN APPROACHING MESOSCALE
CONVECTIVE VORTEX -- OR MCV -- LOCATED ACROSS NORTHWEST IA WHICH
HAS LEAD TO A LINEAR THUNDERSTORM BAND ACROSS NORTHERN IA OVER THE
PAST SEVERAL HOURS, BEST CAPTURED BY THE 21Z AND 00Z RUNS OF THE
HRRR MESOSCALE GUIDANCE.  PRECIPITABLE WATER VALUES -- PWS -- OF
1.50 INCHES HAVE POOLED NEAR THE ELEVATED WARM FRONT.  FLASH FLOOD
GUIDANCE VALUES ARE AROUND TWO INCHES IN THREE HOURS' TIME ACROSS
THE REGION, WHICH COULD BE EXCEEDED AS THIS BAND TRAINS FOR 2-3
HOURS ACROSS THE REGION.  CLOUD TOPS CONTINUE TO COOL IN
ASSOCIATION WITH THIS THUNDERSTORM ACTIVITY AS IT EVOLVES INTO A
MESOSCALE CONVECTIVE SYSTEM -- MCS. THE SYSTEM HAS BEEN MOVING
EASTWARD AT AROUND 20 KNOTS -- ABOUT DOUBLE THE RATE OF
PROGRESSION INDICATED BY CORFIDI/PROPAGATION VECTORS -- AHEAD OF A
PROGRESSIVE UPPER-LEVEL SHORTWAVE.  THE RAP MESOSCALE GUIDANCE
INDICATES THAT LOW-LEVEL INFLOW SHOULD WEAKEN AFTER 12Z/6 AM CDT
TODAY; CHOSE A 1320Z/720 AM CDT EXPIRATION TIME FOR THIS AREA IN
CASE CONVECTION LINGERS FOR LONGER THAN THE RAP'S MASS FIELDS
SUGGEST.  RECENT HISTORY FOR THIS SYSTEM INDICATES THAT LOCAL
RAINFALL AMOUNTS OF 2-4 INCHES ARE POSSIBLE WHERE CELLS TRAIN NEAR
THE EASTERN IA/MN BORDER AND SOUTHERN WISCONSIN, WHICH COULD LEAD
TO FLASH FLOODING.

ROTH


ATTN...WFO...GRB...MKX...DVN...ARX...MPX...DMX...

LAT...LON   43729415 44479329 44739100 44198865 42758860 42509070
            42849323 43729415 


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