MESOSCALE PRECIPITATION DISCUSSION 0227...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
206 AM EDT THU AUG 29 2013

CORRECTED FOR MISSING WORD
 
AREAS AFFECTED...SOUTHERN ND...NORTHEAST SD...WESTERNMOST MN 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 290605Z - 291205Z
 
SUMMARY...BACKBUILDING CONVECTION IS POSSIBLE ACROSS SOUTHERN ND
BEGINNING AROUND 08Z, AND CONTINUING TOWARDS 12Z NEAR THE ND/SD
BORDER AS IT STRETCHES TOWARDS MN, WITH RAINFALL RATES OF 1-2
INCHES PER HOUR EXPECTED.  REGIONAL FLASH FLOODING IS POSSIBLE.

DISCUSSION...A BURGEONING THUNDERSTORM COMPLEX NEAR THE ND/MT
BORDER IS EXPECTED TO MOVE SOUTH OF DUE EAST THROUGH THE REMAINDER
OF THE NIGHT/EARLY MORNING, REMAINING ELEVATED NORTH OF A SURFACE
FRONT BOUNDARY DUE TO EXISTING CIN, PER THE LAST COUPLE RUNS OF
THE ARW, AND CLOSER TO ITS 850 HPA SLICE.  CLOUD TOPS CONTINUE TO
EXPAND AND COOL ON RECENT SATELLITE IMAGERY, INDICATING ITS
CONTINUED DEVELOPMENT.  VAD WIND PROFILES FROM SD HAVE BEEN
INTERESTING, WITH RAPID CITY SD SHOWING THE 850 HPA INFLOW
INCREASING TO 35 KNOTS AN HOUR AGO, BEFORE RECENTLY RELAXING.  THE
04Z RAP INDICATES THAT THERE SHOULD BE ANOTHER INCREASE IN THE
LOW-LEVEL INFLOW SHORTLY BACK UP TO 35 KNOTS, WHICH SHOULD RESULT
IN 0-3 KM SHEAR IN THE RANGE OF 40 KNOTS.  CAPE WITHIN THE 03Z RAP
AND 00Z ARW INDICATE THAT VALUES NEAR THE CURRENT COMPLEX ARE
AROUND 2000 J/KG, THOUGH VALUES DOWNSTREAM NEAR THE ND/SD BORDER
ARE EXPECTED TO BE IN THE 3000-4000 J/KG RANGE.  THIS COMBINATION
OF LOW-LEVEL WIND SHEAR AND CAPE WOULD RESULT IN WET MICROBURSTS,
BOW ECHOES, OR DERECHOES, IMPLYING THAT THE COMPLEX SHOULD KEEP
MOVING ALONG.

HOWEVER, AN INCREASING LOW-LEVEL JET SHOULD ALLOW FOR BACKBUILDING
ON ITS SOUTHWEST PERIPHERY BETWEEN 08Z-12Z FAIRLY CLOSE TO THE
ND/SD BORDER, WHICH COULD LEAD TO REGIONAL FLASH FLOODING AND
COULD FORM A LENGTHENING RAIN BAND IN THAT AREA.  THE 00Z GFS
CORFIDI VECTORS DO SHOW WEAKENING CONVECTIVE PROPAGATION FOR THIS
REASON.  PRECIPITABLE WATER VALUES OF 1.75-2 INCHES EXIST ACROSS
THE REGION, ABOVE THE 90TH PERCENTILE FOR LATE AUGUST, WHICH
SHOULD ALLOW FOR ABOVE AVERAGE PRECIPITATION EFFICIENCY.  RAINFALL
RATES ARE EXPECTED TO BE IN THE 1-2 INCH PER HOUR RANGE, WHICH
WOULD EXCEED FLASH FLOOD GUIDANCE, WITH LOCAL AMOUNTS OF 2-4
INCHES POSSIBLE WITHIN A SHORT TIME FRAME.  SINCE THE EVENT HAS
NOT BEGUN TO UNFOLD YET, CONFIDENCE IS NO BETTER THAN AVERAGE,

ROTH

ATTN...WFO...FGF...ABR...BIS...

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

LAT...LON   45539670 45539969 46300198 47580187 47809969 46899720
            45539670