MESOSCALE PRECIPITATION DISCUSSION 0703
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
729 PM EDT WED AUG 16 2017

AREAS AFFECTED...SOUTHEAST MN & WEST-CENTRAL WI

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

VALID 162329Z - 170529Z

SUMMARY...THUNDERSTORMS WITH COOLING CLOUD TOPS ARE SHOWING SOME
OCCASIONAL CELL TRAINING ACROSS SOUTHEAST MN.  HOURLY RAIN TOTALS
TO 1.5" WITH LOCAL AMOUNTS TO 3" ARE EXPECTED.

DISCUSSION...AN OCCLUDED CYCLONE IS LIFTING INTO SOUTHWEST MN AT
THE PRESENT TIME.  NON-OPERATIONAL GOES-16 IMAGERY SHOWS COOLING
CLOUD TOPS WITH THE ACTIVITY, AND RADAR HAS SHOWN OCCASIONAL
TRAINING AND CELL MERGERS WITHIN SOUTH-CENTRAL MN.  PRECIPITABLE
WATER VALUES ARE ~1.5".  MU CAPES IN THE AREA ARE 500-1500 J/KG. 
INFLOW AT 850 HPA IS CYCLONIC UP TO 35 KTS, NEAR THE MAGNITUDE OF
THE MEAN 850-400 HPA WIND.  SINCE THE CYCLONE IS DEEP LAYERED, THE
FLOW IS UNIDIRECTIONAL WITH HEIGHT.  A COUPLE OBSERVATIONS
INDICATE HOURLY RAIN RATES UP TO 1.5" IN SOME OF THIS ACTIVITY PER
REPORTS FROM THE MPX/CHANHASSEN MN AND ARX/LA CROSSE WI FORECAST
OFFICES.

THE MESOSCALE GUIDANCE APPEARS TOO HIGH ACROSS SOUTHWEST MN AND
EASTERN SD PER THE MU CAPE VALUES PRESENT, WHICH ARE UNLIKELY TO
INCREASE FROM HERE ON OUT.  CIN SHOULD DEVELOP WITH TIME TO HELP
FOCUS ACTIVITY ALONG THE 850 HPA SLICE OF THE OCCLUSION, WHICH
SHOULD KEEP PUSHING SLOWLY NORTHWARD.  HOWEVER, THE GUIDANCE
APPEARS REASONABLE ACROSS SOUTHEAST MN AND WEST-CENTRAL WI PER
CURRENT TRENDS.  THE 12Z SSEO NEIGHBORHOOD PROBABILITIES OF
EXCEEDING THE THREE HOUR FLASH FLOOD GUIDANCE PEAK IN THE 70%+
RANGE BETWEEN 00-04Z BEFORE FADING, LIKELY DUE TO DECREASING
INSTABILITY, A NARROWING MOISTURE CHANNEL, AND AN INVADING DRY
SLOT.  HOURLY RAIN TOTALS UP TO 1.5" WITH LOCAL AMOUNTS TO 3" ARE
EXPECTED, WITH SLIGHTLY HIGHER AMOUNTS IN MN THAN WESTERN WI. 
OVERALL, THIS APPEARS TO BE PART OF A LONGER DURATION HEAVY RAIN
EVENT.

ROTH

ATTN...WFO...ARX...GRB...MKX...MPX...

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

LAT...LON   45309229 44849043 44148943 43158927 43009012
            43309238 44019447 45139455