MESOSCALE PRECIPITATION DISCUSSION 0472
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
604 PM EDT FRI AUG 28 2015
 
AREAS AFFECTED......EASTERN IOWA TO SOUTHWEST WI AND NORTHWEST
IL... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 282205Z - 290405Z
 
SUMMARY...HEAVY RAINS ARE LIKELY TO CONCENTRATE OVER NORTHEAST IA
INTO ADJACENT SOUTHWEST WI AND NORTHWEST IL OVER THE NEXT FEW
HOURS. FLASH FLOODING IS POSSIBLE.

DISCUSSION...A BAND OF HEAVY SHOWERS AND EMBEDDED STORMS HAS
PERSISTED OVER CENTRAL TO NORTHEAST IOWA THIS AFTERNOON. 
RADAR IMAGERY SHOWED THE BAND DRIFTING SLOWLY EAST. DUAL-POL RADAR
ESTIMATES WERE ON THE ORDER OF 1 TO 2 INCHES/HR. 2 INCHES OF RAIN
IN 3 HOURS ENDING AT 21Z WAS OBSERVED AT WATERLOO IOWA.  LOCAL
STORM REPORTS FROM THE DES MOINES FORECAST OFFICE INDICATED
REPORTS OF FLASH FLOODING AND SEVERAL INCHES OF RAIN HAD FALLEN IN
THE IMPACTED AREAS OF CENTRAL IA.

THE CONVECTION IS FOCUSED WITHIN A WARM ADVECTION REGIME LOCATED
ON THE NOSE OF A WELL DEFINED 850-700 MB JET. WITH THIS JET AND
THE 20Z RAP SHOWING WELL DEFINED BOUNDARY LAYER MOISTURE
CONVERGENCE FORECAST TO PERSIST OVER THE NEXT SEVERAL HOURS THE
THREAT SHOULD CONTINUE. THE THREAT MAY WANE LATER THIS EVENING AS
MODELS AGREE ON THE JET GRADUALLY WEAKENING WITH TIME...WITH THE
MOISTURE CONVERGENCE RESPONDING BY WEAKENING AS WELL. 

THE LAST SEVERAL RUNS OF THE HRRR HAVE BEEN FORECASTING A FOCUSED
AXIS OF REPEAT CONVECTION THAT PERSISTS WELL INTO THE EVENING. 
LIKEWISE THE 12Z WRF ARW AND NMMB AND SPC WRF ALL FORECAST A BAND
OR BANDS OF HEAVY SHOWERS/LOCALLY HEAVY RAINS. THE HRRR RUNS FROM
16-21Z APPEAR TO BE FOCUSING TOO MUCH RAIN TOO FAR TO THE
NORTHWEST.  

SATELLITE AND RADAR TRENDS WOULD FAVOR THE AXIS OVER EASTERN IA
AND ADJACENT NORTHWEST IL AND SOUTHWEST WI OVER THE NEXT SEVERAL
HOURS.  AN ADDITIONAL 2-4 INCHES OF RAIN IS LIKELY WITH STORM
TOTALS POSSIBLY EXCEEDING 5 INCHES THROUGH THIS EVENING.

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

PETERSEN

ATTN...WFO...ARX...DMX...DVN...LOT...MKX...

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

LAT...LON   42998957 42568921 41829007 41429097 41269187 
            41479259 41799304 42429216 42909098