MESOSCALE PRECIPITATION DISCUSSION 0484
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EDT TUE SEP 08 2015
 
AREAS AFFECTED...NORTHERN IA, SOUTHERN MN, & VICINITY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 080600Z - 081200Z
 
SUMMARY...WIDELY SCATTERED THUNDERSTORMS ARE FORMING AS LOW-LEVEL
INFLOW INCREASES OVER A NEARBY STATIONARY FRONT.  FLASH FLOODING
IS POSSIBLE.

DISCUSSION...INFLOW AT 850 HPA IS RAMPING UP AHEAD OF A
MESOCYCLONE ACROSS SOUTHEAST ND AND ITS ATTENDANT SURFACE
LOW/OUTFLOW BOUNDARY, UP TO 15-25 KTS PER THE LATEST VAD WIND
PROFILES IN THE REGION.  THIS INFLOW IS ADVECTING 1500-2000 J/KG
MUCAPE FROM WEST CENTRAL IA.  ALONG WITH AN APPROACHING SHORTWAVE
AND NEARBY JET STREAK, WIDELY SCATTERED THUNDERSTORMS HAVE BROKEN
OUT NORTH OF A STATIONARY FRONT WHICH ARE MOVING NORTHEAST AT
15-20 KTS.  PRECIPITABLE WATER VALUES IN THE REGION ARE 1.50-1.75"
PER RECENT RAP FORECASTS AND GPS INFORMATION.

RAP GUIDANCE INDICATES INFLOW AT 850 HPA INCREASES TO 25-40 KTS
OVER THE NEXT FEW HOURS BEFORE WANING AFTER 10Z.    THE 00Z CAM
GUIDANCE HAS TRENDED SIGNIFICANTLY WETTER IN THIS REGION, LED BY
THE 00-02Z HRRR RUNS, FORECASTING LOCAL AMOUNTS OF 3-5".  HOURLY
RAIN RATES UP TO 1.75" COULD ALLOW THE RAIN TO FALL QUICKLY.  AS
850 HPA INFLOW RAMPS UP DURING THE NEXT FEW HOURS, BACKBUILDING IS
POSSIBLE, PARTICULARLY NEAR THE INVERTED TROUGH ACROSS WESTERN
IA/SOUTHWEST MN.  FOR THE MOST PART, CELL MERGERS/TRAINING ARE
EXPECTED TO BE THE MAIN FLASH FLOOD CONCERN AS ORGANIZED
CONVECTION IS EXPECTED TO MOVE EAST AT 30-40 KTS PER THE 1000-500
HPA THICKNESS PATTERN AND FORWARD PROPAGATING CONVECTIVE VECTORS. 
THE AVAILABLE INSTABILITY COULD SUPPORT SIX HOURS OF ISSUES NEAR
THE IA/MN BORDER, THOUGH THE 18Z SSEO NEIGHBORHOOD PROBABILITIES
OF EXCEEDING THE THREE HOUR FLASH FLOOD GUIDANCE SUGGEST ISSUES
COULD PERSIST PAST 12Z -- USED A SIX HOUR WINDOW.  AS FLASH FLOOD
GUIDANCE VALUES ARE HIGHER/HARDER TO EXCEED IN THIS REGION, USED
THE POSSIBLE CATEGORY.

ROTH

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

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

LAT...LON   44319311 43459197 41939246 41619677 42499780 
            43289776 43289776 43779693 44079598 44279529