MESOSCALE PRECIPITATION DISCUSSION 0343
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 PM EDT WED SEP 03 2014
 
AREAS AFFECTED...CENTRAL MN & NORTHWEST WI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 031756Z - 032356Z
 
SUMMARY...A REDEVELOPING BAND OF THUNDERSTORMS ACROSS CENTRAL MN
IS EXPECTED TO TRAIN DURING THE AFTERNOON HOURS.  FLASH FLOODING
IS POSSIBLE HERE.

DISCUSSION...AT THE SURFACE, A WARM FRONT ACROSS THE NORTHERN
PLAINS HAS PHASED WITH AN OUTFLOW BOUNDARY ACROSS SOUTHERN MN
CAUSED BY ONGOING MORNING AND EARLY AFTERNOON CONVECTION. 
THUNDERSTORMS REMAIN ELEVATED OVER THE COMBINED/COMPOSITE BOUNDARY
DUE TO SOME SURFACE-BASED CIN, SHOWN BY RECENT RUNS OF THE ARW AND
RAP GUIDANCE AS WELL AS THE RECENT DEVELOPMENT OF A STRATUS FIELD
ACROSS EASTERN SD.  SOME LOW- TO MID-LEVEL CAPPING IS EVIDENT
ACROSS SOUTHWEST MN, USING THE 12C ISOTHERM AT 700 HPA AS A GUIDE.
 INFLOW AT 850 HPA IS 30-35 KNOTS, SIMILAR TO THE MAGNITUDE OF THE
850-400 HPA MEAN WIND, WHICH HAS LED TO SOME PRECIPITATION
EFFICIENCY.  PRECIPITABLE WATER VALUES ARE RISING IN THIS REGION,
GENERALLY BETWEEN 1.25-1.50".  MOST UNSTABLE CAPE VALUES OF
1000-2000 J/KG EXIST ACROSS SOUTHERN MN AND SD.  OVERALL, THE
ENVIRONMENT JUST MEETS THE CRITERIA FOR THE WET MULTICELL
ENVIRONMENT.

THE MESOSCALE GUIDANCE HAS HAD A DIFFICULT TIME HANDLING THIS
CONVECTION SO FAR TODAY WITHIN ITS 00Z-12Z RUNS, SHOWING AMOUNTS
THAT HAVE BEEN MUCH TOO LIGHT PER RADAR ESTIMATES.  BELIEVE THE
12Z REGIONAL CANADIAN MODEL, 12Z SPC WRF, 12Z NSSL WRF ARE DOING
THE BEST JOB AS OF LATE FOR AREA AND AMOUNTS FORECAST.  THE
FORECAST REMAINS FOR A WEST-EAST BAND OF THUNDERSTORMS TO PERSIST
WHICH COULD SLOWLY LIFT NORTH THROUGH CENTRAL MN OVER THE NEXT
SEVERAL HOURS, REMAINING SOMEWHAT ELEVATED OVER THE WARM
FRONT/OUTFLOW BOUNDARY.  TRAINING REMAINS THE POSSIBLE CAUSE FOR
POTENTIAL FLASH FLOODING AS CELLS CONTINUE TO REGENERATE NEAR THE
WESTERN END OF THE MPD AREA WHERE CAPE VALUES, PRECIPITABLE WATER
VALUES, AND LOW-LEVEL INFLOW ARE HIGHEST EARLY ON.  HOURLY RAIN
RATES UP TO 1.75" ARE SUPPORTED BY THE AVAILABLE MOISTURE, WITH
THE BETTER PERFORMING GUIDANCE SO FAR INDICATING LOCAL AMOUNTS OF
2-4" BEING POSSIBLE WITHIN A SHORT PERIOD OF TIME.  THIS COULD
LEAD TO FLASH FLOODING.

ROTH

ATTN...WFO...ABR...DLH...FGF...MPX...

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

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            45099407 45019533 44919598 45149644 45369696 
            46419663 46939514