Flash Flood Guidance
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000
AWUS01 KWNH 222340
FFGMPD
ILZ000-WIZ000-IAZ000-NEZ000-230354-

MESOSCALE PRECIPITATION DISCUSSION 0310
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
740 PM EDT FRI AUG 22 2014

AREAS AFFECTED...EASTERN NE/IA/SOUTHWESTERN WI/NORTHERN IL...

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

VALID 222339Z - 230354Z

SUMMARY...WITHIN A VERY UNSTABLE ENVIRONMENT...CONVECTION
CONTINUES TO FIRE ALONG A STATIONARY BAROCLINIC ZONE STRETCHING
THROUGH CENTRAL IA. SLOW FORECAST CELL MOTIONS MAY LEAD TO
EPISODES OF TRAINING AND BACKBUILDING. CONFIDENCE IS LOW IN THE
EVOLUTION OF THIS EVENT BUT THE THREAT IS DEFINITELY THERE.

DISCUSSION...THE 23Z SURFACE ANALYSIS SHOWED A SHARP BAROCLINIC
ZONE STRETCHING THROUGH MUCH OF CENTRAL IA AND BACK DOWN INTO
SOUTHEASTERN NE AND NORTH-CENTRAL KS. STRONG LOW-LEVEL CONVERGENCE
WAS OBSERVED ALONG THE ENTIRE BOUNDARY WITH VERY HIGH MOISTURE IN
PLACE. DEWPOINTS RANGING FROM 75F TO NEARLY 80F WERE OBSERVED
ACROSS THE REGION WITHIN A VERY UNSTABLE ENVIRONMENT. THE 23Z RAP
OBJECTIVE ANALYSIS INDICATED 3000 TO 4000 J/KG OF SURFACE-BASED
CAPE ACROSS THE REGION. EXPERIMENTAL 1 MINUTE GOES-14 SUPER RAPID
SCAN IMAGERY SHOWED MUCH OF THIS CAPE IS BEING REALIZED AS A
NUMBER OF STORM UPDRAFTS CONTINUE TO GROW RAPIDLY. THE KOAX RADAR
DERIVED ECHO TOPS PROVIDE SOME TRUTH TO THE UPDRAFT STRENGTH WITH
VALUES APPROACHING 58 KFT IN THE STRONGER CORES. RADAR-DERIVED
HOURLY RATES ARE IN THE 2 TO 3 INCH RANGE WHICH SOUNDS ABOUT RIGHT
GIVEN THE MAGNITUDE OF THE UPDRAFTS AND SLOW CELL MOTIONS.

THE COMBINATION OF PWATS IN THE 2 TO 2.25 INCH RANGE WITH
INSTABILITY WHICH IS EXPECTED TO LINGER BEYOND 03Z SHOULD HELP
MAINTAIN THE ACTIVITY UNTIL AFTER DARK. THE BIGGEST ISSUE WORKING
AGAINST THIS COMPLEX IS THE WEAK LOW-LEVEL INFLOW. UNLIKE THE
PREVIOUS NIGHT WHICH HAD 30 TO 35 KNOTS OF LOW-LEVEL FLOW...THE
23Z RAP ONLY FORECASTS 10 TO 15 KNOTS THROUGHOUT THE NIGHT.
HOWEVER...THERE IS ENOUGH SIGNAL IN THE HIGH-RESOLUTION MODELS OF
HEAVY RAINFALL OVERNIGHT THAT AN MPD IS WARRANTED. FUTURE SHIFTS
WILL ASSESS THE SITUATION TONIGHT.


RUBIN-OSTER

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

ATTN...WFO...LOT...MKX...DVN...ARX...DMX...FSD...OAX...

ATTN...RFC...LMRFC...MBRFC...NCRFC...OHRFC...

LAT...LON   42589586 42789498 42959376 43179015 42218886 41508915
            41359014 41319186 41179310 40959457 40789525 40639597
            40589656 40739702 41129717 41819707 42329637 42589586


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