MESOSCALE PRECIPITATION DISCUSSION 0453
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
752 AM EDT TUE AUG 18 2015
 
AREAS AFFECTED...WESTERN IA & VICINITY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 181151Z - 181451Z
 
SUMMARY...SATELLITE AND RADAR TRENDS SHOW A SLIGHT UPTICK IN
HOURLY RAIN RATES WITHIN THIS REGION.  AS THE CONVECTION MOVES
INTO A MORE SATURATED AREA, FLASH FLOODING IS POSSIBLE.

DISCUSSION...A COUPLE OF MERGING CONVECTIVE AREAS ARE SEEN IN
RECENT SATELLITE IMAGERY BETWEEN SOUTHEAST SD AND WESTERN IA. 
INFLOW AT 850 HPA OF 25-35 KTS IS SEEN STREAMING INTO THE REGION
PER VAD WIND PROFILES, NEAR THE MAGNITUDE OF THE MEAN 850-400 HPA
WIND.  PRECIPITABLE WATER VALUES OF 1.5-1.75" HAVE BEEN REPORTED
BY GPS.  MUCAPE IN THE REGION IS IN THE 500-1000 J/KG, WHICH IS
SUFFICIENT WITHIN THIS MOIST ENVIRONMENT.

THE 06Z SSEO NEIGHBORHOOD PROBABILITIES SUGGEST POTENTIAL FLASH
FLOOD ISSUES THROUGH 15Z, BEFORE FADING -- USED A THREE HOUR
WINDOW DUE TO THIS EXPECTATION.  THIS APPEARS TO BE DUE TO FADING
INSTABILITY ACROSS THE REGION.  HOURLY RAIN RATES UP TO 1.75"
REMAIN POSSIBLE, WHICH IS MOST LIKELY EARLY IN THE PERIOD DUE TO
POSSIBLE CELL MERGERS AND COULD EXCEED THE THREE HOUR FLASH FLOOD
GUIDANCE IN SATURATED AREAS ACROSS NORTHWEST IA.  THE LATEST
MESOSCALE QPF GUIDANCE ADVERTISES LOCAL AMOUNTS IN THE 2-4" RANGE
THROUGH THE REMAINDER OF THE MORNING, WHICH COULD FALL QUICKLY. 
IT APPEARS THE 00Z NMMB AND 00Z ARW (ALONG WITH THEIR PARALLEL
RUNS) ARE BEST PLACED BASED ON CURRENT CONVECTIVE LOCATION, THE
POSITION OF SURFACE FEATURES, AND THE EXPECTED PROGRESSION OF THE
850 HPA SLICE OF THE FRONTAL BOUNDARY BASED ON RECENT RAP RUNS. 
NEW CONVECTION IS EXPECTED LATER TODAY FARTHER EASTWARD ACROSS IA
AS INSTABILITY REBUILDS LATER TODAY, WHICH WILL BE WATCHED FOR
LATER MPD POSSIBILITIES.

ROTH

ATTN...WFO...DMX...EAX...FSD...OAX...

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

LAT...LON   43319600 42869377 41809247 40549345 40549490 
            41099648 42059774 42989724