MESOSCALE PRECIPITATION DISCUSSION 0329
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1208 AM EDT SAT JUN 11 2016
 
AREAS AFFECTED...PORTIONS OF NORTHEAST IA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 110408Z - 110908Z
 
SUMMARY...SHORT PERIODS OF CELL TRAINING COULD LEAD TO HOURLY RAIN
RATES UP TO 2", WITH LOCAL AMOUNTS IN THE 3-5" RANGE.  THIS COULD
LEAD TO FLASH FLOODING.

DISCUSSION...THE MESOSCALE/CAM GUIDANCE HAS BEEN OF LITTLE USE IN
THIS PART OF THE COUNTRY.  AN OUTFLOW BOUNDARY MOVING ACROSS IA IS
ACTING AS A FOCUS FOR LIFT FOR ELEVATED THUNDERSTORMS WITH COOLING
CLOUD TOPS.  HOWEVER, LEFT OVER INSTABILITY AHEAD OF A WEAK
FRONTAL ZONE ACROSS MN IS FEEDING THE THUNDERSTORMS FROM THEIR
REAR FLANK, WHICH HAS LED TO PERIODS OF CELL TRAINING ACROSS
NORTHEAST IA.  PRECIPITABLE WATER VALUES ARE 1.6-2" IN THIS AREA
PER RAP FORECAST FIELDS AND GPS DATA.  INFLOW AT 850 HPA IS
CONVERGENT, FROM THE NORTHWEST AT 10-20 KTS ACROSS NORTHEAST IA
AND WEST-SOUTHWEST AT 25-30 KTS ACROSS SOUTHERN IA AND SOUTHEAST
NE.

WHILE MOST OF THE GUIDANCE HAS BEEN MISPLACED WITH THIS ACTIVITY
(AT THE VERY LEAST), THE 18Z SSEO NEIGHBORHOOD PROBABILITIES OF
EXCEEDING THE THREE HOUR FLASH FLOOD GUIDANCE SHOWED A WEAK SIGNAL
IN THE AREA THROUGH 09Z.  THE 01Z HRRR EXPERIMENTAL AND 03Z HRRR
RUNS APPEAR TO BE HANDLING THIS THE BEST, THOUGH THEIR MAGNITUDE
OF LOCAL AMOUNTS APPEARS LOW.  THE 18Z GFS-BASED GALVEZ-DAVISON
INSTABILITY INDEX ALSO INDICATED VALUES OF 40+ THROUGH 09Z, WHICH
USUALLY INDICATES A FLASH FLOOD THREAT.  IN NORTHEAST IA, CELL
MOTION SHOULD BE SOUTHEASTERLY, THOUGH ACROSS WESTERN IA, A SLOW
SOUTH TO SOUTHWEST DRIFT IS EXPECTED TO CONTINUE.  THE MESOSCALE
WAVE HAS MOVED SOUTHEAST FROM SD INTO NORTHWEST IA OVER THE PAST
FEW HOURS, A MOTION WHICH IS PRESUMED TO CONTINUE AS LONG AS
CONVECTION REMAINS ACROSS THE REGION.  HOURLY RAIN RATES UP TO 2"
ARE POSSIBLE WHERE SHORT TRAINING BANDS SET UP, WITH LOCAL AMOUNTS
IN THE 3-5" RANGE POSSIBLE OVER THE NEXT SEVERAL HOURS.  DUE TO
THE POOR SIGNAL IN THE MESOSCALE GUIDANCE, CONFIDENCE IS BELOW
AVERAGE IN THIS AREA.  

ROTH

ATTN...WFO...ARX...DMX...DVN...FSD...MPX...

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

LAT...LON   43529400 43529224 43459129 42529072 41519090 
            41499310 42669616 43389609 43509537