MESOSCALE PRECIPITATION DISCUSSION 0376...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
643 PM EDT THU JUN 28 2018

CORRECTED FOR VALID TIME

AREAS AFFECTED...EAST-CENTRAL MT & NORTHWEST ND

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

VALID 282241Z - 290441Z

SUMMARY...THUNDERSTORMS ARE INCREASING IN COVERAGE ACROSS PORTIONS
OF EAST-CENTRAL MT & NORTHWEST ND.  HOURLY RAIN TOTALS TO 2" WITH
LOCAL AMOUNTS TO 4" ARE EXPECTED OVER THE NEXT SEVERAL HOURS.

DISCUSSION...THUNDERSTORMS ARE GROWING IN COVERAGE NORTH OF A PAIR
OF SURFACE WAVES ACROSS EAST-CENTRAL MT, AHEAD OF A SHARP UPPER
TROUGH MOVING THROUGH WESTERN ID AND NV.  OTHER STORMS ARE
SPLITTING ACROSS NORTHWEST ND.  PRECIPITABLE WATER VALUES HAVE
INCREASED TO 0.8-1.1" IN THE HIGH PLAINS OF MT PER GPS VALUES AND
ARE NEAR 1.5" IN ND PER RAP ANALYSES.  INFLOW AT 850 HPA IS
INCREASING OUT OF THE SOUTHEAST PER VAD WIND PROFILES, AT 15-20
KTS.  MORE IMPORTANTLY IS THE EFFECTIVE BULK SHEAR, WHICH IS 40-70
KTS PER SPC MESOANALYSES.  IMPRESSIVE ML CAPE VALUES ARE FEEDING
INTO THE CONVECTION FROM THE WARM SECTOR, IN THE RANGE OF
2000-6500 J/KG.

NOW THAT CONVECTION HAS INITIATED, THE NORTHWARD PROGRESSION OF
THE INSTABILITY GRADIENT SHOULD SLOW/STOP IN THE NEAR TERM. 
INFLOW AT 850 HPA SHOULD CONTINUE TO STRENGTHEN WITH TIME
EXCEEDING THE MEAN 850-400 WIND BY 03Z, WITH CONVECTION ADDING TO
THE AVAILABLE MOISTURE IN THE COLUMN.  THE DEGREE OF INSTABILITY
AND BULK SHEAR ARGUES FOR SUPERCELLS AND ULTIMATELY A BOW
ECHO/QLCS/LEWP AROUND THE END OF THE PERIOD ONCE A COLD POOL FORMS
AND THUNDERSTORMS MERGE/CONGEAL INTO A LARGER COMPLEX.  WITH THE
EXPECTATION FOR SUPERCELLS AND CELL MERGERS, THE DEGREE OF
MOISTURE AVAILABLE SUPPORTS HOURLY RAIN TOTALS TO 2".  THE
GUIDANCE WITH THE BEST HANDLE OF THIS ACTIVITY SO FAR HAS BEEN THE
12Z NMMB WHICH HAS CAPTURED ITS MORE WESTERN INITIATION.  ELEMENTS
OF THE HRRR, RAP, AND NAM CONEST APPEAR USEFUL WITH TIME, SO
UTILIZED THOSE FOR MPD AREA DEPICTION.

ROTH

ATTN...WFO...BIS...BYZ...GGW...TFX...

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

LAT...LON   49070397 48960051 47470100 46560576 46210816
            46810958 48060966 48930769