Graphic for MPD #0218

MESOSCALE PRECIPITATION DISCUSSION 0218
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
633 PM EDT MON MAY 15 2017

AREAS AFFECTED...SOUTHERN MN...NORTHERN IA...SOUTHERN WI

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

VALID 152232Z - 160332Z

SUMMARY...SLOW-MOVING THUNDERSTORMS WITH HEAVY RAINFALL RATES UP
TO 2 INCHES PER HOUR WILL CAUSE SOME CONCERNS FOR FLASH FLOODING
THROUGH THE EVENING HOURS ACROSS PARTS OF THE UPPER MIDWEST.

DISCUSSION...THUNDERSTORMS ARE BEGINNING TO INCREASE IN INTENSITY
AND COVERAGE NEAR A SLOW MOVING WARM FRONT OVER NORTHERN IOWA AND
EXTENDING EASTWARD ACROSS SOUTHERN WISCONSIN.  SURFACE BASED CAPE
VALUES ARE ON THE ORDER OF 3000 J/KG JUST SOUTH OF THIS BOUNDARY
PER THE SPC MESOANALYSIS.  THE LATEST RAP MODEL GUIDANCE SUGGEST
THAT 850MB INFLOW FROM THE SSW WILL INCREASE TO AROUND 30 KTS
LATER THIS EVENING, AND THIS WILL INTERACT WITH THE FRONT AND
SUSTAIN THE CONVECTION WITHIN THIS VERY UNSTABLE AIRMASS MOVING
INTO NORTHERN IOWA AND SOUTHERN WISCONSIN OVER THE NEXT SEVERAL
HOURS.  SOME OF THIS HEAVY RAINFALL MAY EXTEND INTO EXTREME
SOUTHEAST MINNESOTA AS WELL.  THREE-HOUR FLASH FLOOD GUIDANCE
VALUES ARE AS LOW AS 1.5 INCHES ACROSS PARTS OF THIS REGION.

PW VALUES OF AROUND 1.3 TO 1.6 INCHES AND THE HIGH INSTABILITY
WILL FAVOR RAINFALL RATES AS HIGH AS 2 INCHES PER HOUR.  AN
ADDITIONAL CONCERN WILL BE THE LIKELY REPEATED ROUNDS OF
CONVECTION IN THE VICINITY OF THIS BOUNDARY GIVEN THE
BACK-BUILDING TENDENCIES OBSERVED ON RECENT RADAR IMAGERY.  THIS
WILL RESULT IN LOCALLY HEAVY RAINFALL TOTALS THROUGH THE EVENING. 
THE LATEST HRRR OPERATIONAL AND EXPERIMENTAL GUIDANCE APPEARS TO
BE UNDERDONE WITH THIS ACTIVITY, WHEREAS THE ARW AND NMMB APPEAR
TO HAVE A BETTER HANDLE ON THE SITUATION.  AS SUPPORTED BY THE ARW
AND NMMB, RAINFALL TOTALS OF 1 TO 3 INCHES, WITH ISOLATED HIGHER
AMOUNTS, CAN BE EXPECTED THROUGH 10PM CENTRAL TIME. THIS WILL BE
ENOUGH TO RESULT IN CONCERNS FOR FLASH FLOODING AND PARTICULARLY
OVER AREAS THAT HAVE RECEIVED HEAVY RAIN EARLIER TODAY. 

HAMRICK

ATTN...WFO...ARX...DMX...DVN...FSD...GRB...MKX...MPX...

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

LAT...LON   44309002 44298849 43928785 43208780 42748796
            42568828 42558967 42579029 42489112 42219196
            42009304 41979382 42189455 42659497 43199490
            43679405 43949206


Last Updated: 633 PM EDT MON MAY 15 2017