MESOSCALE PRECIPITATION DISCUSSION 0040...CORRECTION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
147 AM EDT FRI MAY 17 2013
 
AREAS AFFECTED...IA/MN BORDER 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 170546Z - 170946Z
 
SUMMARY...HEAVY RAINFALL AND RESULTANT FLASH FLOODING IS POSSIBLE
ALONG THE MN/IA BORDER OVER THE NEXT SEVERAL HOURS.

DISCUSSION...LOW-LEVEL INFLOW INTO A FRONTAL BOUNDARY AT THE 850
HPA LEVEL HAS INCREASED AHEAD OF AN APPROACHING MESOSCALE
CONVECTIVE VORTEX -- OR MCV -- WHICH IS LEADING TO A NEW ROUND OF
LINEAR THUNDERSTORM ACTIVITY NEAR THE IA/MN BORDER, BEST CAPTURED
BY THE 21Z AND 00Z RUNS OF THE HRRR MESOSCALE GUIDANCE.  THE
LATEST RUNS OF THE ARW AND NMM ARE MISSING OUT ON THIS CONVECTIVE
ACTIVITY.  PRECIPITABLE WATER VALUES -- PWS -- OF 1.50 INCHES ARE
POOLING NEAR THE ELEVATED WARM FRONT.  FLASH FLOOD GUIDANCE VALUES
OF 1.5-2 INCHES IN THREE HOURS' TIME ACROSS THE REGION COULD BE
EXCEEDED BY THIS NEW ROUND OF PRECIPITATION.  THE EXPECTATION IS
THAT A NEW MESOSCALE CONVECTIVE SYSTEM -- MCS -- WILL BE FORMING
AROUND 06Z/1 AM CDT FROM THIS LINEAR BAND AND MOVE SLOWLY EASTWARD
AT 5-10 KNOTS (THE VECTOR ADDITION OF PROPAGATION/CORFIDI VECTORS
AND THE NORTHWARD MIGRATION OF THE 850 HPA WARM FRONT) AHEAD OF A
PROGRESSIVE UPPER-LEVEL SHORTWAVE.  SINCE THE GUIDANCE CAN
SOMETIMES BE TOO SLOW IN PROPAGATING CONVECTION, ELONGATED THE
AREA ALONG THE LENGTH OF THE IA/MN BORDER TO ACCOUNT FOR THE
FORECAST UNCERTAINTY.  LOCAL RAINFALL AMOUNTS OF 1.5-3 INCHES ARE
POSSIBLE WHERE CELLS TRAIN NEAR THE IA/MN BORDER, WHICH COULD LEAD
TO FLASH FLOODING.

ROTH


ATTN...WFO...ARX...MPX...DMX...FSD...

LAT...LON   43629651 44349604 44669331 44309121 43119071 42539292
            42909567 43629651