MESOSCALE PRECIPITATION DISCUSSION 0448
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SUN AUG 16 2015
 
AREAS AFFECTED...NORTHEASTERN NE/SOUTHEASTERN SD/SOUTHERN
MN/NORTHWESTERN IA... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 161859Z - 162159Z
 
SUMMARY...CONVECTION CONTINUES TO GENERATE ALONG THE LEADING EDGE
OF A WEAK MID/UPPER-LEVEL SHORTWAVE NOTED IN WATER VAPOR IMAGERY.
THE ACTIVITY HAS FOCUSED ALONG A HIGH PWAT PLUME EXTENDING ACROSS
THE REGION. WITH SOILS GRADUALLY BECOMING SATURATED FROM RAINFALL
THE PREVIOUS 24 HOURS...EXPECT THE POTENTIAL FOR FLASH FLOODING.

DISCUSSION...A SLOW-MOVING COLD FRONT CONTINUES TO MARCH EASTWARD
IN THE PRESENCE OF 1.50 TO 1.75 INCH PWATS STRETCHING FROM
CENTRAL/EASTERN NE UP THROUGH EASTERN SD/SOUTHERN MN. ALTHOUGH
BUOYANCY HAS BEEN LIMITED WITH MUCAPE VALUES IN THE 500 TO 1000
J/KG RANGE...HIGHLY EFFICIENT UPDRAFTS HAVE BEEN ABLE TO PRODUCE
LOCALLY HEAVY RAINFALL ACROSS THE REGION. CONVECTIVE DEBRIS HAS
LIMITED SURFACE HEATING FOR THE MOST PART EXCEPT FOR EASTERN
NE/NORTHWESTERN IA WITH 18Z TEMPERATURES SOARING INTO THE MID 80S.
SOME CU DEVELOPMENT HAS BEEN SEEN IN THE REGIONS OF DIMINISHED
CLOUD COVER BUT THERE IS STILL A BIT OF INHIBITION LEFT TO
OVERCOME. EXPECT THE AREAL COVERAGE OF CONVECTION TO EXPAND
FURTHER INTO THE AFTERNOON AS THE BAROCLINIC ZONE WORKS ITS WAY
SLOWLY TOWARD THE EAST. CORFIDI VECTORS REMAIN SMALL THE NEXT
HOURS SUGGESTING THE THREAT FOR TRAINING. ADDITIONALLY...LOW-LEVEL
FLOW DOES NOT APPEAR TO BE AN ISSUE AS THE VWP DATA OUT OF OMAHA
NE SHOWED 20 TO 25 KNOTS OF SOUTH-SOUTHWESTERLY FLOW IMPINGING ON
THE BOUNDARY.

THERE IS A LOOSE SIGNAL IN THE CAMS SUGGESTING THE HEAVY RAINFALL
THREAT INTO THE EVENING HOURS. THE LIMITED INSTABILITY WILL LIKELY
BE THE BIGGEST NEGATING FACTOR TO SEEING MORE WIDESPREAD COVERAGE
OF CONVECTION. WILL ALLOW THE EVENING SHIFT TO RE-ASSESS THE
CONVECTIVE TRENDS AND OBSERVATIONAL DATA FOR A POSSIBLE
RE-ISSUANCE.


RUBIN-OSTER

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LAT...LON   45879432 45199333 43619504 41489757 41609867 
            42589801 43549759 43989672 44869546