Flash Flood Guidance
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000
AWUS01 KWNH 230753
FFGMPD
MNZ000-IAZ000-SDZ000-231200-

MESOSCALE PRECIPITATION DISCUSSION 0187
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
353 AM EDT WED MAY 23 2018

AREAS AFFECTED...NORTH-CENTRAL IA...SOUTHWEST TO SOUTH-CENTRAL MN

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

VALID 230750Z - 231200Z

SUMMARY...SLOW-MOVING AND REPEATING SHOWERS AND THUNDERSTORMS WILL
POSE AT LEAST SOME FLASH FLOODING CONCERNS GOING THROUGH DAWN.

DISCUSSION...THE UPPER MIDWEST REGION IS UNDER A BROAD WARM AIR
ADVECTION PATTERN WITH DEEPER LAYER SOUTH TO SOUTHWEST FLOW
RETURNING UP ACROSS THE PLAINS WHICH IS TRANSPORTING FAVORABLE
LEVELS OF MOISTURE AND INSTABILITY NORTHWARD AND OVER A
WELL-DEFINED QUASI-STATIONARY FRONTAL ZONE.

THE LATEST RADAR AND GOES-16 SATELLITE IMAGERY ARE SHOWING AN
EXPANSION OF CONVECTION WITH VERY COLD CLOUD TOPS IN A NW/SE
FASHION TO THE NORTHEAST OF THIS FRONT. THE ACTIVITY IS FOCUSING
ALONG A WELL-DEFINED ELEVATED INSTABILITY GRADIENT AND AT THE NOSE
OF A SOUTHWEST LOW LEVEL JET OF ABOUT 30 KTS. PWATS ACROSS THE
REGION HAVE RISEN TO NEAR 1.3 TO 1.5 INCHES AND IS HELPING TO
FACILITATE HEAVY RAINFALL RATES. IN FACT...THIS COUPLED WITH SOME
OVERSHOOTING TOP ACTIVITY IS CONTRIBUTING TO RAINFALL RATES OF AS
MUCH AS 2 TO 2.5 INCHES/HR. IN FACT...ESTERVILLE IA (KEST)RECENTLY
REPORTED 2.29 INCHES IN LESS THAN 1 HOUR.

OVER THE NEXT FEW HOURS...THE LOW LEVEL JET SHOULD REMAIN RATHER
STEADY STATE WHICH WILL FOSTER SPEED CONVERGENCE ALONG WITH
FAVORABLE MOISTURE/INSTABILITY TRANSPORT OVER THE AFOREMENTIONED
BOUNDARY FOR SUSTAINABLE CONVECTION. THE CELLS ARE RELATIVELY
ANCHORED ALONG THE SAME AXIS WITH ONLY A VERY SLOW EASTWARD SHIFT
NOTED TO THE CONVECTIVE AXIS OVER THE LAST HOUR...AND THERE WILL
BE CONCERNS FOR AT LEAST SOME PERIODIC TRAINING OR REPEATING OF
CONVECTIVE CELLS.

THE VERY INTENSE RAINFALL RATES AND SLOW MOVEMENT OF THE OVERALL
CONVECTIVE AXIS WILL PROMOTE SOME VERY HEAVY RAINFALL TOTALS THAT
MAY REACH AS HIGH AS 3 TO 4 INCHES WITH ISOLATED HEAVIER AMOUNTS
GOING THROUGH 12Z. THIS WILL PROMOTE A CONCERN FOR AT LEAST SOME
FLASH FLOODING. WILL CONTINUE TO MONITOR.

ORRISON

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

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

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

LAT...LON   44869582 44699461 44129353 43149259 42459254
            42109286 42089337 42189359 42459395 42969451
            43259491 43629550 44019620 44479647 44739633




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