MESOSCALE PRECIPITATION DISCUSSION 0451
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 PM EDT SUN AUG 16 2015
 
AREAS AFFECTED...NORTHWEST IOWA...EXT SE SOUTH DAKOTA...EXT SOUTH
CENTRAL MINNESOTA...EXT NORTHEAST NEBRASKA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 170400Z - 170900Z
 
SUMMARY...MOST SIGNIFICANT THREAT WINDING DOWN IN MAGNITUDE AND
AREAL COVERAGE...YET SOME WEAK SIGNALS REMAIN FOR ISOLATED
FLOODING CONCERNS IN THE EARLY OVERNIGHT PERIOD. 

DISCUSSION...OVERALL SETUP REMAINS DYNAMICALLY ACTIVE FOR
CONTINUED ASCENT ACROSS THE DISCUSSION AREA YET INSTABILITY IS
REDUCING FOR STRONGER CONVECTIVE DEVELOPMENT AND HIGH RAIN RATES. 
SYNOPTIC SETUP SHOWS WEAK SHORTWAVE FEATURE ACROSS EASTERN SD/NEB
BOARDER WITH MESOSCALE OUTFLOW CHANNEL FEEDING THE MAIN EXITING
JET STREAK ACROSS THE NORTHERN PLAINS.  THIS SHORTWAVE AND
ASSOCIATED UPPER JET STREAK CONTINUE TO PROVIDE EXCELLENT BROAD
SCALE ASCENT ACROSS THE REGION FOR EXPANSION OF MODERATE CLOUD
SHIELD PRECIPITATION PARTICULARLY AS DIVERGENCE FIELDS ARE
FORECAST TO INCREASE THROUGH THE 04-09Z TIME PERIOD ACROSS THE
DISCUSSION AREA AND N INTO CENTRAL MN.  ADDITIONALLY...THE
LOCATION OF THE JET AXIS AND SHORTWAVE ARE REDUCING LOWER LEVEL
HEIGHTS AND SURFACE PRESSURES FOR A WEAK INFLECTION TO DEVELOP IN
THE 850-700MB WIND FLOW AS SEEN IN FSD VWP AND SURROUNDING
STATIONS WITH NEAR ZERO FLOW AT FSD AT 850.  THIS IS ALLOWING FOR
A WEAKLY VEERED LOW LEVEL ENVIRONMENT FOR A SIGNIFICANT AND
CONTINUED E-W MOISTURE CONVERGENCE LINE TO FOCUS STRONGER ASCENT
AND TAP WEAK MID-LEVEL INSTABILITIES ACROSS NORTHWEST IA... WITH
MUCAPES STILL IN THE 500 J/KG RANGE.  IT IS ALONG THIS BOUNDARY
THAT MOST FOCUSED CONTINUED FLASH FLOOD THREAT SHOULD REMAIN. 
HOWEVER...FORECAST FROM RAP/HRRR INDICATE MUCH OF THE INSTABILITY
WILL BE USED BY 09Z...REDUCING RATES...TO BROADER ASCENT/MODERATE
SHOWERY ACTIVITY.  VERY HIGH MOISTURE AVAILABLILITY THROUGH A DEEP
LAYER PER CIRA LAYERED TPW...SHOULD MAKE FOR EFFICIENT RAINFALL
PRODUCTION WITH .5-1"/HR RATES IN MODERATE SHIELD ASCENT VERSUS
1.5-2"/HR IN REMAINING ACTIVE CONVECTIVE CORES. 

GALLINA

ATTN...WFO...DMX...FSD...MPX...OAX...

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

LAT...LON   44089436 44019342 43029311 42169409 41499562 
            41779670 42269695 43329623