MESOSCALE PRECIPITATION DISCUSSION 0657
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
601 AM EDT FRI SEP 09 2016
 
AREAS AFFECTED...SOUTHERN MN...NORTHERN IA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 091000Z - 091600Z
 
SUMMARY...INCREASED CONVECTIVE COVERAGE AND SOME WEST TO EAST
TRAINING MAY RESULT IN AN ISOLATED FLASH FLOOD THREAT THIS MORNING.

DISCUSSION...CONVECTION IS EXPANDING THIS MORNING ACROSS SOUTHERN
MN. A SUBTLE SHORTWAVE FEATURE IS RESULTING IN ENHANCED LOW LEVEL
MOISTURE TRANSPORT INTO A STATIONARY WEST TO EAST BOUNDARY. THIS
SOUTHWESTERLY FLOW IS ALSO ADVECTING STEEP MID LEVEL LAPSE RATES
INTO THE AREA...RESULTING IN MUCAPE VALUES APPROACHING 2000 J/KG.
THIS COMBINED WITH INCREASING UPPER LEVEL DIVERGENCE IN THE RIGHT
ENTRANCE REGION OF A STRENGTHENING UPPER JET...IS RESULTING IN THE
INCREASED CONVECTIVE COVERAGE. STORM MOTIONS ARE GENERALLY
PARALLEL TO THE BOUNDARY...RESULTING IN SOME TRAINING OVER THE
NEXT SEVERAL HOURS AHEAD OF THE WAVE. PRECIPITABLE WATER
VALUES...WHILE NOT TOO IMPRESSIVE...HAVE INCREASED TO NEAR
1.5"...WHICH IS STILL AROUND 1.5 STANDARD DEVIATIONS ABOVE NORMAL.
THIS IS STILL ENOUGH TO RESULT IN HOURLY RAINFALL TOTALS AROUND
1-2" WHERE TRAINING OCCURS.

THE ARW AND NSSL ARW HAVE A ROUGH HANDLE ON THE SITUATION...AND
BOTH SUGGEST LOCAL AMOUNTS OF 2-5" THROUGH 16Z NEAR THE MN/IA
BORDER. CURRENT FORECASTS SUGGEST A WEAKENING OF THE LOW LEVEL
INFLOW INTO THE BOUNDARY AFTER 16Z AS THE WAVE MOVES OFF TO THE
EAST...ALONG WITH A DECREASE IN THE UPPER LEVEL DIVERGENCE
SIGNATURE. THUS WOULD SEEM LIKE WE COULD SEE A LULL IN CONVECTIVE
ACTIVITY FOR A PERIOD AFTER 16Z. HOWEVER MODEL GUIDANCE IS IN
AGREEMENT THAT ANOTHER ROUND OF CONVECTION WILL FIRE SHORTLY AFTER
ALONG THE EASTWARD MOVING COLD FRONT. AMOUNTS FORECAST THROUGH 16Z
COULD RESULT IN AT LEAST ISOLATED FLASH FLOODING GIVEN THE
RELATIVELY LOW FLASH FLOOD GUIDANCE OVER THE REGION...AND COULD
ALSO HELP SATURATE THE GROUND...INCREASING A POSSIBLE FLASH FLOOD
THREAT FROM ANY SECOND ROUND OF CONVECTION THIS AFTERNOON. WPC
WILL CONTINUE TO MONITOR RADAR/SATELLITE AND MODEL TRENDS.

CHENARD

ATTN...WFO...ARX...DMX...FSD...MPX...

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

LAT...LON   44809142 44699104 44289074 43459124 43149305 
            43069480 43749557 43909541 44319483 44689285