MESOSCALE PRECIPITATION DISCUSSION 0447
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1023 AM EDT SUN AUG 16 2015
 
AREAS AFFECTED...EASTERN SD/EXTREME NORTHERN NE/NORTHWESTERN
IA/SOUTHWESTERN MN 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 161423Z - 161853Z
 
SUMMARY...IMPRESSIVE AXIS OF EARLY MORNING CONVECTION ACROSS AREAS
OF EASTERN SD/SOUTHWESTERN MN. THE EXPECTATION OF SLOW CELL
MOTIONS COMBINED WITH A RATHER HIGH PWAT AIR MASS SUPPORTS A
THREAT FOR FLASH FLOODING. 

DISCUSSION...THE 14Z SURFACE ANALYSIS INDICATED A WAVE OF LOW
PRESSURE MOVING THROUGH HURON SD. COLD FRONTAL BOUNDARIES EXTENDED
TOWARD THE SOUTHWEST AND NORTHEAST WHILE NUMEROUS OUTFLOW
BOUNDARIES WERE EVIDENT IN THE LOCAL WIND FIELDS. VISIBLE
SATELLITE IMAGERY THIS MORNING SHOWED A VERY INTENSE UPDRAFT IN
CLOSE PROXIMITY TO THE SURFACE LOW WHERE CLOUD TOPS IN THE PAST
HOUR HAVE REACHED -75C. THIS ACTIVITY HAS CONTINUED TO EXPAND
TOWARD THE EAST IN THE MOISTURE RICH AIR MASS. THIS AXIS OF HIGH
PWAT AIR HAS BEEN NARROW IN NATURE BUT QUITE FOCUSED WITH VALUES
NEARING 2 INCHES OVER THE SIOUX FALLS SD AREA BASED ON GPS DATA.
MODEST INSTABILITY IS IN PLACE OVER THE REGION OF ACTIVE
CONVECTION WITH MUCAPE VALUES GENERALLY AROUND 1000 J/KG. A
SIGNIFICANT CLOUD CANOPY OVERSPREADING THE REGION SHOULD INITIALLY
LIMIT THE SURFACE HEATING. HOWEVER...DEEP-LAYERED MOISTURE WITH
FREEZING LEVELS ABOVE 13 KFT INDICATE WARM RAIN PROCESSES WILL BE
PLENTY SUFFICIENT FOR HEAVY RAINFALL THIS MORNING/AFTERNOON.
FORECAST CORFIDI VECTORS OVER THE REGION ARE QUITE SMALL AS THE
MEAN STEERING FLOW ALIGNS WITH THE STORM RELATIVE INFLOW.

THE 12Z HRRR RESOLVED THE EARLY MORNING ACTIVITY QUITE WELL WHILE
SHOWING POSSIBLE TRAINING THROUGH AT LEAST 18Z.
FURTHER...SLOW-MOVING/TRAINING CONVECTION HAS ALREADY OCCURRED
OVER SOUTHWESTERN MN WHERE 6 INCHES OF RAIN HAS FALLEN. SATURATED
SOILS FROM PREVIOUS HEAVY RAINFALL WILL MAKE FLASH FLOODING MORE
LIKELY ACROSS THESE LOCATIONS. WILL RE-ASSESS THE SITUATION IN THE
EARLY AFTERNOON FOR A POSSIBLE RE-ISSUANCE.


RUBIN-OSTER

ATTN...WFO...ABR...DMX...FSD...LBF...MPX...OAX...UNR...

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

LAT...LON   45339586 45049460 44019431 43339468 43019568 
            42989696 42809817 42469932 43449983 44599921 
            45299763