Flash Flood Guidance
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000
AWUS01 KWNH 020343
FFGMPD
WIZ000-MNZ000-IAZ000-SDZ000-020843-

MESOSCALE PRECIPITATION DISCUSSION 0475
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1143 PM EDT TUE SEP 01 2015

AREAS AFFECTED...MINNESOTA AND IOWA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 020343Z - 020843Z

SUMMARY...FLASH FLOODING IS POSSIBLE OVERNIGHT AS DEEP CONVECTION
EXPANDS AND TRAINING AND BACK BUILDING INCREASE.

DISCUSSION...INTENSE CONVECTION CONTINUES TO SLOWLY EXPAND IN
VICINITY OF A MESOLOW OVER SOUTHWEST MINNESOTA WITH COLD POOL
GENERATION CONTRIBUTING TO ENHANCED STORM RELATIVE FLOW.

DESPITE WEAK AND IN SOME CASES LOW MODEL QPFS...OBSERVATIONAL
SIGNALS FOR MORE WIDESPREAD DEVELOPMENT OVERNIGHT EXISTS...GIVEN A
SMALL BUT PRONOUNCED SHORTWAVE TROUGH INFLUENCING THE
REGION...MUCAPES NEAR OR IN EXCESS OF 3000 J/KG...AND A MODERATE
TO STRONG LOW LEVEL JET.

GIVEN EARLY FORMATION OF THE MESOLOW ALONG WITH STEEP LOW LEVEL
LAPSE RATES TO PROVIDE ADDITIONAL COLD POOL DEVELOPMENT AND THUS A
SLOPING SURFACE FOR THE INTENSIFYING LOW LEVEL JET TO ASCEND...ITS
APPEARS PROBABLE THAT CONVECTION WILL EXPAND ACROSS THE REGION
OVERNIGHT.  RAIN RATES MAY EASILY EXCEED 2 INCHES PER HOUR GIVEN
THE HIGH CAPES...AND POSSIBLY ADDITIONAL MESOCYCLONE DEVELOPMENT.
OBSERVED AND MODEL WIND PROFILES SHOW MOSTLY VEERING WINDS AT THE
MOMENT...THUS SUPPORTING TRAINING...WHILE LATER TONIGHT WINDS ARE
EXPECTED TO BECOME SLIGHTLY MORE UNIDIRECTIONAL...WHICH WOULD
SUPPORT MORE BACKBUILDING...AND LONGER EPISODES OF VERY HIGH RAIN
RATES WHICH MAY EVENTUALLY EXCEED LOCAL FFG VALUES AND CONTRIBUTE
TO FLASH FLOODING.

JAMES

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

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

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

LAT...LON   45799630 45649423 44559191 42969205 42759440
            43229576 44639660


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