MESOSCALE PRECIPITATION DISCUSSION 0449
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
741 PM EDT SUN AUG 16 2015
 
AREAS AFFECTED...E-CNTRL NEBRASKA INTO NWRN IOWA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 162340Z - 170430Z
 
SUMMARY...THE THREAT FOR FLASH FLOODING IS INCREASING FROM CNTRL
NEBRASKA INTO NWRN IOWA AND EXTREME SRN MINNESOTA. HIGH
PRECIPITABLE WATER VALUES WILL SUPPORT RAINFALL RATES UP TO 2.5
IN/HR WITH PERIODS OF TRAINING CONVECTION THROUGH 04Z.

DISCUSSION...AT 23Z...SURFACE OBSERVATIONS PLACED A
QUASI-STATIONARY FRONT SWWD ACROSS NWRN IOWA INTO CNTRL NEBRASKA
WITH TWO WELL DEFINED OUTFLOW BOUNDARIES OUT AHEAD OF THE FRONT.
THE AREA OF CONCERN IS FROM E-CNTRL NEBRASKA INTO NWRN IOWA WHERE
DAYTIME HEATING HAS ALLOWED MLCAPE VALUES TO RISE TO ESTIMATED
VALUES OF 1000 TO 2000 J/KG PER RECENT RAP/SPC MESOANALYSES. RADAR
TRENDS SHOWED INCREASING CONVECTIVE ACTIVITY ALONG THE OUTFLOW
BOUNDARY LOCATED IN NWRN IOWA WHICH IS A CONCERN GIVEN 850-700 MB
FLOW OF 20-30 KTS PARALLEL TO THIS BOUNDARY...AND PARALLEL TO THE
CLOUD BEARING MEAN FLOW. GIVEN THIS INSTABILITY AND PRECIPITABLE
WATER VALUES NEAR 2 INCHES...RAINFALL RATES OVER 2 IN/HR WILL BE
POSSIBLE.

RECENT RAP FORECASTS SUPPORT UNIDIRECTIONAL SOUTHWEST LOW-MID
LEVEL FLOW ACROSS NEBRASKA INTO IOWA PERSISTING INTO THE EARLY
OVERNIGHT HOURS...ALONG WITH DIFFLUENT FLOW ALOFT...AS THE REGION
SITS BENEATH THE EDGE OF THE UPPER RIDGE AXIS. WETTER TRENDS IN
THE HRRR HAVE SUPPORTED THE ARGUMENT OF TRAINING CONVECTION WITH 3
HOURLY RAINFALL TOTALS OF 3-4 INCHES IN E-CNTRL NEBRASKA AND NWRN
IOWA. THIS DOES NOT SEEM UNREASONABLE GIVEN SATELLITE/RADAR
TRENDS...MOISTURE AVAILABILITY AND ESTIMATED INSTABILITY...AND
GIVEN THE HRRR HAS CAUGHT ON TO PLACEMENT OF MESOSCALE OUTFLOW
BOUNDARIES.

OTTO

ATTN...WFO...ARX...DMX...FSD...GID...LBF...MPX...OAX...

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

LAT...LON   44249289 43589218 41649449 40559708 40069908 
            40240011 41149963 42349660 43959444