MESOSCALE PRECIPITATION DISCUSSION 0045
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1027 PM EDT SAT MAY 18 2013
 
AREAS AFFECTED...CENTRAL SD AND CENTRAL/SOUTHEAST ND 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 190115Z - 190715Z
 
SUMMARY...ORGANIZED ASCENT AND SLOW STORM MOTIONS EXPECTED
THROUGHOUT THE NIGHT. LOCAL FLASH FLOODING IS LIKELY...WITH AN
ENHANCED RISK WHERE HEAVY RAIN FELL EARLIER SATURDAY.

DISCUSSION...MODELS HAVE DIFFERED ON THE PLACEMENT OF HEAVY RAIN
IN THE NORTHERN PLAINS TONIGHT...BUT RECENT OBSERVATIONAL TRENDS
GIVE US SOME CONFIDENCE TO PREDICT AN AXIS OF HEAVY RAIN AND AN
ATTENDANT RISK OF FLASH FLOODING FROM CENTRAL SD TO SOUTHEAST ND.

THE 18Z GFS FINDS SUPPORT FROM THE RAP AND FROM 00Z RAOBS IN
SUGGESTING CYCLOGENESIS WILL OCCUR OVER WESTERN SOUTH DAKOTA
TONIGHT...WITH AN AXIS OF LOW LEVEL CONVERGENCE PERSISTING LONGER
OVER THIS REGION THAN SOME OTHER MODELS SUCH AS THE 12Z ECMWF HAD
FORECAST. THE GFS PRODUCES A HEALTHY SWATH OF 1-INCH OR GREATER OF
QPF...AREALLY AVERAGED...THROUGH 12Z. THIS IS NEARLY COINCIDENT
WITH THE WPC FORECAST. PLACING TRUST IN THE GFS AND RAP MASS
FIELDS...0-6 KM MEAN WINDS AND UPWIND PROPAGATION VECTORS REMAIN
VERY LIGHT THROUGH 06Z. SLOW MOTIONS WERE ALREADY
OBSERVED...ESPECIALLY WHERE ONGOING CONVECTION INTERCEPTED AN
OUTFLOW BOUNDARY LEFT BY THE EARLY MORNING ACTIVITY SOUTHWEST OF
PIERRE SD.

SPC MESOANALYSIS AND SREF/GFS/RAP MASS AND QPF FIELDS SUGGEST
AMPLE INSTABILITY AND LOW LEVEL EASTERLY INFLOW WILL EXIST TO
SUSTAIN AN EASTWARD MOVING LINE OF CONVECTION...WITH TRAINING FROM
SW TO NE ALONG THE LINE. THE FLUX OF UNSTABLE AIR INTO THIS REGION
IS GREATEST OVER SOUTH DAKOTA...TOWARD AREAS OF LOWEST FLASH FLOOD
GUIDANCE AROUND 1-2 INCHES IN 3 HOURS. PER EARLIER DISCUSSION FROM
NESDIS SAB AND AVERAGING HIRES GUIDANCE...LOCAL STORM TOTALS OF
2-4 INCHES ARE POSSIBLE.

BURKE


ATTN...WFO...FGF...FSD...ABR...BIS...UNR...

LAT...LON   47319687 47369912 47160008 46340120 45540220 44510248
            43930245 43550169 43779995 44289890 44819858 45639792
            45949728 46089696 46639663 47319687