MESOSCALE PRECIPITATION DISCUSSION 0132
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
713 PM EDT TUE JUN 17 2014
 
AREAS AFFECTED...SOUTHEAST SD, MN/IA BORDER, AND SOUTHWEST WI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 172312Z - 180512Z
 
SUMMARY...CONVECTIVE INITIATION IS EXPECTED ACROSS SOUTHEAST SD BY
01Z, WHICH SHOULD SPREAD AND/OR ADVECT EASTWARD INTO SOUTHWEST WI
BY 05Z.  NUMEROUS INSTANCES OF FLASH FLOODING ARE POSSIBLE DESPITE
ITS EVENTUAL FORWARD PROGRESSION DUE TO SATURATED SOILS IN THE
REGION.

DISCUSSION...THUNDERSTORMS WITH HEAVY RAINFALL ARE EXPECTED TO
FORM ACROSS SOUTHEAST SD AND NEAR THE MN/IA BORDER OVER THE NEXT
FEW HOURS AS 850 HPA INFLOW DOUBLES -- WELL EXCEEDING THE 850-400
HPA MEAN WINDS -- INTO/OVER A STATIONARY FRONT LOCATED ACROSS
NORTHERN NE AND CENTRAL IA, FEEDING IN PRECIPITABLE WATER VALUES
NEAR 2" AND CAPE VALUES 4000-6000 J/KG.  THE DRY LINE IS EXPECTED
TO MIX EASTWARD THROUGH CENTRAL NE OVER THE NEXT HOUR OR TWO,
WHICH COULD ACT AS ONE OF THE FOCI OF STORM INITIATION IN THIS
REGION.  WARM TEMPERATURES AT 700 HPA ARE EXPECTED TO MAINTAIN CIN
ALONG THE FRONTAL BOUNDARY ITSELF, ELEVATING THE CONVECTION CLOSER
TO ITS 850 HPA SLICE.  THE ABOVE  COMBINATION OF INDICES EXPECTED
IS NORMALLY BEYOND THE SCOPE OF THE WET MULTI-CELL ENVIRONMENT,
AND STRONGLY IMPLIES FORWARD PROPAGATION.

WHILE THE COLD POOL FORMS AND UNTIL FORWARD PROPAGATION CAN BE
REALIZED, CELLS SHOULD SHOW SOME TENDENCY TO BACKBUILD DUE TO THE
INCREASING 850 HPA INFLOW AND WARM THICKNESS BUBBLE NEAR THE
EASTERN BORDER OF SD AND NE.  THE 12Z OAX SOUNDING INDICATED THE
WET BULB ZERO HEIGHT WAS NEAR 11,000 FEET ABOVE GROUND LEVEL,
IMPLYING WARM RAIN PROCESSES COULD BE AT PLAY IN THIS REGION. 
HOURLY RAINFALL RATES OF 2.5" WITHIN THIS MOIST AIRMASS ARE
EXPECTED WITH STRONGER STORMS, WHICH WOULD EASILY OVERWHELM THE
LOW FLASH FLOOD GUIDANCE CAUSED BY RECENT HEAVY RAINFALL OVER THE
PAST FEW DAYS.  THE MESOSCALE QPF GUIDANCE SHOWED SOLUTIONS STREWN
ACROSS NE/SD EASTWARD INTO IL -- TRIED TO USE RAP AND ARW MASS
FIELDS TO SUPPLEMENT THE DISAGREEABLE GUIDANCE.  NUMEROUS
INSTANCES OF FLASH FLOODING ARE POSSIBLE.

ROTH

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

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

LAT...LON   42919056 42739444 42759781 43259868 44589782 44849391
            44369060 42919056