MESOSCALE PRECIPITATION DISCUSSION 0478
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1222 AM EDT SUN SEP 06 2015
 
AREAS AFFECTED...SOUTHWEST ND & VICINITY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 060421Z - 060821Z
 
SUMMARY...A THUNDERSTORM COMPLEX MOVING OUT OF EASTERN MT COULD
YIELD HOURLY RAIN RATES UP TO 1.5" WITH LOCAL TOTALS UP TO 3". 
FLASH FLOODING IS POSSIBLE.

DISCUSSION...A MATURING CONVECTIVE COMPLEX HAS BEEN MOVING THROUGH
THE RADAR GAP ACROSS SOUTHEAST MT, TO THE NORTHEAST OF A FRONTAL
WAVE ALONG AN INVERTED TROUGH/WEAK THERMAL GRADIENT.  STORM
MOTIONS HAVE BEEN VARIED, ROUGHLY TO THE NORTHEAST AT 30 KTS,
THOUGH THERE ARE THE BEGINNING SIGNS OF FORWARD PROPAGATION IN
RECENT RADAR IMAGERY AND THE FORMATION OF A COLD POOL IN THE 04Z
SURFACE OBSERVATIONS.  PRECIPITABLE WATER VALUES IN THE AREA ARE
1.25", NEAR THE LOWER THRESHOLD FOR BROADER FLASH FLOOD ISSUES IN
THIS REGION, WHICH WOULD SUPPORT HOURLY RAIN RATES UP TO 1.5". 
MUCAPES NEAR AND EAST OF THE SYSTEM ARE IN THE 1000-2000 J/KG
RANGE.

THE CAM GUIDANCE SHOWS LOCAL AMOUNTS OF 1.5-3" ARE POSSIBLE IN
THIS REGION, WHICH COULD OCCUR QUICKLY.  THESE AMOUNTS COULD
RESULT FROM SHORT PERIODS OF CELL TRAINING AND CELL MERGERS AS THE
NET MOTION OF THE HEAVIEST RAIN RATES BECOMES MORE EAST-NORTHEAST
AT 30 KTS.  BASED ON CONVERGENCE FIELDS FROM RECENT RAP RUNS AND
ALLOWING FOR FORWARD PROPAGATION, BELIEVE THE GUIDANCE IS TOO FAR
NORTH WITH ITS RAINFALL FOOTPRINT.  CONSIDERING THE LOW FLASH
FLOOD GUIDANCE VALUES, 1-1.5" WITHIN THREE HOURS, BELIEVE FLASH
FLOODING IS POSSIBLE.

ROTH

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

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

LAT...LON   47980194 47850070 47390046 46470062 45740183 
            45490343 45610399 45650410 47290362