Flash Flood Guidance
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000
AWUS01 KWNH 281610
FFGMPD
IAZ000-282205-

MESOSCALE PRECIPITATION DISCUSSION 0471
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1209 PM EDT FRI AUG 28 2015

AREAS AFFECTED...IA

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

VALID 281605Z - 282205Z

SUMMARY...VERY HEAVY RAINS ARE LIKELY TO CONCENTRATE OVER CENTRAL
IA THE NEXT FEW HOURS. SOME FLASH FLOODING AND RUNOFF PROBLEMS ARE
POSSIBLE.

DISCUSSION...IR SATELLITE IMAGERY HAS SHOWN A BLOSSOMING OF COLDER
CLOUD TOPS ACROSS PORTIONS OF CENTRAL IA IN PARTICULAR ALONG WITH
A BIT OF A CONVECTIVE WEDGE SIGNATURE. RADAR IMAGERY SHOWS AN AREA
OF REPEATING AND BACKBUILDING SHOWERS AND THUNDERSTORMS OVER THIS
AREA...AND DUAL-POL RADAR ESTIMATES ARE ON THE ORDER OF 1 TO 2
INCHES/HR. THIS MAY BE A TAD OVERDONE BASED ON ACTUAL SURFACE
OBSERVATIONS...BUT THE PERSISTENCE OF THE CONVECTION IS SUPPORTING
THE RISK OF AT LEAST SOME FLASH FLOODING AND RUNOFF PROBLEMS.

THE CONVECTION IS FOCUSED WITHIN A WARM ADVECTION REGIME JUST
AHEAD OF A WAVE OF LOW PRESSURE AND IS BEING STRONGLY FACILITATED
BY THE ARRIVAL OF A RATHER DYNAMIC SHORTWAVE TROUGH. INSTABILITY
ACROSS CENTRAL IA IS VERY WEAK...BUT OVERALL FORCING IS RATHER
IMPRESSIVE WITH A COMBINATION OF WARM AIR ADVECTION AND DIVERGENT
FLOW ALOFT ASSOCIATED WITH THE SHORTWAVE.

THE LAST COUPLE OF RUNS OF THE HRRR HAVE BEEN STRONGLY SUGGESTIVE
OF AN AXIS OF REPEAT CONVECTION THAT MAY PERSIST WELL INTO THE
AFTERNOON. HOWEVER...THE 14Z HRRR APPEARS TO BE FOCUSING TOO MUCH
RAIN TOO FAR TO THE NORTH. THE 00Z ARW AND 00Z NMMB ALSO HAD
SIMILAR SIGNATURES FOR THIS...BUT AGAIN WITH THE AXIS TOO FAR
NORTH IN THESE MODELS. SATELLITE AND RADAR TRENDS WOULD FAVOR THE
AXIS OVER CENTRAL IA AND PERHAPS EVOLVING INTO NORTHEAST IA OVER
THE NEXT SEVERAL HOURS. THIS IS LIKELY TO RESULT IN SEVERAL INCHES
OF ADDITIONAL RAINFALL AT LEAST LOCALLY...WITH STORM TOTALS
POSSIBLY EXCEEDING 5 INCHES THROUGH LATE-AFTERNOON.

PLEASE SEE THE LATEST NESDIS/SAB DISCUSSION FOR ADDITIONAL
INFORMATION ON THIS EVENT.

ORRISON

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...ARX...DMX...DVN...

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

LAT...LON   43229232 42819117 42149108 41759161 41669246
            41749362 42049475 42489488 43019407


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