MESOSCALE PRECIPITATION DISCUSSION 0304
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
317 AM EDT THU AUG 21 2014
 
AREAS AFFECTED...EXTREME SOUTHEAST ND...NORTHEAST SD...CENTRAL AND
SOUTHERN MN...NORTHEAST IA...FAR WESTERN WI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 210705Z - 211000Z
 
SUMMARY...HEAVY SHOWERS AND THUNDERSTORMS WILL EXPAND IN COVERAGE
AND INCREASE IN INTENSITY OVER THE NEXT COUPLE OF HOURS. SOME
FLASH FLOODING IS EXPECTED WHERE CELL MERGERS AND TRAINING OCCUR.

DISCUSSION...A GRADUALLY INCREASING SWLY LOW LEVEL JET WHICH IS
UPWARDS OF 40 KTS BASED ON REGIONAL VAD WIND PROFILER DATA IS
FOSTERING SUFFICIENTLY STRONG WARM AIR ADVECTION INVOF A FRONTAL
ZONE FOR AN INCREASINGLY ORGANIZED CLUSTER OF HEAVY SHOWERS AND
THUNDERSTORMS. MUCH OF THE ACTIVITY THROUGH THE LATE EVENING WAS
FOCUSED OVER NRN SD AND SRN ND...BUT OVER THE LAST COUPLE HOURS
THERE HAS BEEN A RAPID EXPANSION OF COLD CONVECTIVE TOPS OVER WRN
MN IN ASSOC WITH THE NOSE OF THE SWLY LOW LEVEL JET INTERSECTING
THE WARM FRONT.

THE UPR LEVELS OF THE ATMOS ARE RATHER DIFFLUENT AS PER WV/IR SAT
IMAGERY WHICH APPEARS TO BE THE RESULT OF SHORTWAVE ENERGY
ENTERING WRN ND. THIS WILL PROVIDE DEEPER LYR ASCENT OVERNIGHT IN
CONJUNCTION WITH SUSTAINABLE WARM AIR ADVECTION FOR ADDITIONAL
CONVECTION. IN FACT...THE 00Z NAM-CONEST AND 00Z NSSL-WRF BOTH
SUGGEST A ROBUST MCS IMPACTING CNTRL/SRN MN BY AROUND 09Z AND
CONTINUING IN AN ESEWD FASHION THROUGH 12Z. BOTH OF THESE MODELS
SUGGEST RAINFALL POTENTIAL ON THE ORDER OF 3 TO 5 INCHES...AND
THIS IS NOT UNREALISTIC BASED ON THE LATEST SAT/RADAR TRENDS.

ADDITIONAL CONVECTIVE DEVELOPMENT IS POSSIBLE AS FAR SOUTHEAST AS
NERN IA AND WRN WI OVER THE NEXT COUPLE OF HOURS...BUT THE MAIN
CONCENTRATION SHOULD BE OVER CNTRL/SRN MN WHERE THE BEST LOW LVL
JET AND THERMODYNAMIC ENVIRONMENT WILL BE FOCUSED.

THE LARGER SCALE FLOW PATTERN SUPPORTS CELL-MERGERS AND TRAINING
CONVECTION OVERNIGHT...AND WITH RAINFALL RATES UP TO 2
INCHES/HR...THERE WILL BE A CONCERN FOR FLASH FLOODING. WILL
CONTINUE TO MONITOR.

ORRISON

ATTN...WFO...DLH...ARX...MPX...DMX...FGF...FSD...ABR...

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

LAT...LON   45989337 44749143 43919081 43179086 42829175 42859268
            43389429 44049592 44969752 45769776 46479679 46509513
            45989337