MESOSCALE PRECIPITATION DISCUSSION 0269
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1129 PM EDT FRI OCT 04 2013
 
AREAS AFFECTED...NORTHEAST IA...SOUTHEAST MN...WESTERN WI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 050329Z - 050709Z
 
SUMMARY...A LENGTHENING AND SLIGHTLY MOBILE BAND OF THUNDERSTORMS
FROM NORTHEAST IA INTO SOUTHWEST WI WITH HOURLY RAINFALL RATES OF
2-3" AN HOUR COULD CAUSE REGIONAL FLASH FLOODING ACROSS THE UPPER
MISSISSIPPI VALLEY.

DISCUSSION...A LENGTHENING THUNDERSTORM BAND FROM NORTHEAST IA
ACROSS SOUTHEAST MN INTO WESTERN WI HAS DEVELOPED NEAR AND NORTH
OF A WARM FRONT, WITH THE ACTIVITY DRIFTING SLOWLY EASTWARD.  THE
MESOSCALE GUIDANCE WAS UNANIMOUS IN SUPPORT OF THIS THUNDERSTORM
AREA'S FORMATION.  RAINFALL RATES PER RADAR ESTIMATES AND SURFACE
REPORTS ARE 2-3" AN HOUR IN STRONGER CELLS, WHICH EXCEED LOCAL
FLASH FLOOD GUIDANCE VALUES.  THESE STORMS HAVE FORMED IN RESPONSE
TO 50 KTS OF INFLOW (PER VAD WIND PROFILES) AND CAPE VALUES OF
1000-1500 J/KG (PER THE 12Z ARW).  PRECIPITABLE WATER VALUES NEAR
1.50 INCHES ARE ABOVE THE 90TH PERCENTILE FOR EARLY OCTOBER IN
THIS AREA.  DIVERGENCE ALOFT IS SIGNIFICANT TO THE EAST OF A DEEP
CYCLONE ACROSS SD.

CORFIDI VECTORS SUGGEST AN EASTWARD DRIFT SHOULD CONTINUE FOR THE
NEXT SEVERAL HOURS, WHILE THE WARM FRONT'S PROGRESSION AND
INCREASING CIN WITH TIME SHOULD CAUSE A NORTHEAST SHIFT OF THE
CONVECTIVE BAND OVER THE NEXT SEVERAL HOURS.  OTHER STORMS MOVING
IN FROM THE WEST COULD LEAD TO RENEWED HEAVY RAINS OVER AREAS
WHICH RECENTLY RECEIVED 3 INCHES OF RAINFALL ACROSS SOUTHEAST MN. 
THE 12Z ARW ADVERTISES CAPE BECOMING EXHAUSTED AROUND 06Z, WHILE
THE LAST FEW RUNS OF THE HRRR INDICATE CONVECTIVE ACTIVITY SHOULD
PERSIST UNTIL AROUND 07Z.  THE EXPECTATION IS THAT THE COMBINATION
OF A BROKEN BAND OF SEVERE THUNDERSTORMS ALONG A COLD FRONT MOVING
IN FROM THE WEST AND DECREASING CAPE VALUES OVERNIGHT SHOULD END
THE FLASH FLOOD THREAT AROUND 07Z, WHICH WAS USED AS THE
EXPIRATION TIME FOR THIS MPD.

ROTH

ATTN...WFO...GRB...ARX...MPX...DMX...

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

LAT...LON   44598955 43229096 42869245 43449305 44399217 45199051
            44598955