MESOSCALE PRECIPITATION DISCUSSION 0286
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
801 PM EDT SUN JUN 10 2018

AREAS AFFECTED...WESTERN & CENTRAL DAKOTAS

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 110000Z - 110600Z

SUMMARY...THUNDERSTORMS WITH SOME SUPERCELLULAR STRUCTURE CONTINUE
TO EXPAND/BROADEN IN COVERAGE NEAR A COLD FRONT.  HOURLY RAIN
TOTALS TO 2" WITH LOCAL AMOUNTS TO 3" ARE EXPECTED OVER THE NEXT
FEW HOURS.

DISCUSSION...A SLOW-MOVING COLD FRONT AND AN ASSOCIATED
NEGATIVELY-TILTED UPPER TROUGH HAVE BEEN AIDING CONVECTIVE
DEVELOPMENT DURING THE PAST 1-2 HOURS, WHICH IS EXPANDING IN
COVERAGE ACROSS THE WESTERN DAKOTAS.  EMBEDDED SUPERCELLS ARE
SPLITTING WHICH IS ADDING TO POSSIBLE ISSUES AND ATTEMPTING TO
BROADEN THE BAND.  PRECIPITABLE WATER VALUES ARE ESTIMATED TO BE
1.25-1.5" IN THE AREA, WHICH ROUGHLY TRANSLATES TO THE HOURLY RAIN
TOTALS RECEIVED LATELY PER RADAR ESTIMATES ACCOUNTING FOR POSSIBLE
HAIL CONTAMINATION.  INFLOW AT 850 HPA IS SOUTH-SOUTHEAST AT 35
KTS, NEARLY DOUBLE THE MEAN 850-400 HPA WIND.  ML CAPE VALUES ARE
2500-5000 J/KG PER RECENT SPC MESOANALYSES.  EFFECTIVE BULK SHEAR
OF 25-50 KTS LIES ACROSS THE AREA.

LOW- TO MID-LEVEL FRONTOGENESIS IS EXPECTED TO BE RELATIVELY WELL
ALIGNED THROUGH 09Z, WHICH SHOULD AID CONVECTIVE DEVELOPMENT. 
CELL TRAINING, MERGERS, AND MESOCYCLONES COULD ALL CONTRIBUTE TO
THE HEAVY RAIN THREAT IN THIS REGION.  WHILE THE LOW-LEVEL INFLOW
HAS SOME EASTERLY COMPONENT FOR THE NEXT FEW HOURS, FORWARD
PROGRESSION SHOULD BE SLOW TO OCCUR OFF TO THE EAST EVEN IF A COLD
POOL FORMS IN THE MEANTIME.  AVAILABLE INSTABILITY SHOULD ALLOW
FOR THE FORMATION OF A LARGE MCS OVER THE DAKOTAS IN THE NEXT
SEVERAL HOURS.  FORWARD PROPAGATION OFF TO THE EAST SHOULD BECOME
INCREASINGLY POSSIBLE TOWARDS THE END OF THE PERIOD AS THE 850 HPA
FLOW BECOMES MORE SOUTHERLY AND LOSES ITS EASTERLY COMPONENT. 
HOURLY RAIN TOTALS TO 2" WITH LOCAL AMOUNTS TO 3" ARE POSSIBLE
HERE THROUGH 06Z, WHICH WOULD CHALLENGE THE THREE HOUR FLASH FLOOD
GUIDANCE VALUES. 

ROTH

ATTN...WFO...ABR...BIS...UNR...

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

LAT...LON   49090226 49080039 48480024 47099964 46299935
            44609920 44490202 44740375 46970298 48180298
            48980315