MESOSCALE PRECIPITATION DISCUSSION 0116
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1105 PM EDT FRI JUN 21 2013
 
AREAS AFFECTED...NORTHEASTERN NE...SOUTHEAST SD...NORTHWEST
IA...SOUTHERN MN 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 220304Z - 220704Z
 
SUMMARY...THUNDERSTORM ACTIVITY WHICH IS INCREASING IN COVERAGE
FROM NE INTO MN WILL LEAD TO FLASH FLOODING OVER THE NEXT SEVERAL
HOURS AS IT FURTHER ORGANIZES INTO A MESOSCALE CONVECTIVE SYSTEM.

DISCUSSION...THE LATEST RADAR IMAGERY SHOWS A DEVELOPING LINE OF
THUNDERSTORMS FROM EASTERN NE NORTHEAST INTO SOUTHERN MN.  THIS
ACTIVITY IS SURFACE-BASED ACROSS NE AND SOUTHEAST SD AND MORE
ELEVATED IN MN DUE TO SOME CONVECTIVE INHIBITION NEAR THE SURFACE
FRONT IN NORTHERN IA.  THE MESOSCALE GUIDANCE INDICATES THAT CIN
SHOULD BE LESSENING WITH TIME, WHICH SHOULD MAKE THE ACTIVITY MORE
SURFACE-BASED ACROSS IA.  THERE IS AMPLE DIVERGENCE ALOFT ACROSS
THE REGION TO THE EAST OF AN UPPER LEVEL LOW CENTERED IN ID.  CAPE
VALUES OF 5000-6000 J/KG FEED INTO THE SURFACE BOUNDARY FROM THE
SOUTH, AND PRECIPITABLE WATER VALUES OF 1.5-1.75 INCHES ARE ALSO
AVAILABLE TO INCREASE PRECIPITATION EFFICIENCY IN NORTHEAST NE,
NORTHERN IA AND SOUTHERN MN.  INFLOW AT THE 850 HPA LEVEL IS
AROUND 45 KNOTS -- AND COULD INCREASE SOMEWHAT OVERNIGHT -- WHICH
SHOULD ALLOW THE ACTIVITY TO DEVELOP INTO A MESOSCALE CONVECTIVE
SYSTEM.  THE MAIN INFLOW AXIS IS EXPECTED TO REMAIN RELATIVELY
UNCHANGED OVERNIGHT, INCREASING THE THREAT FOR FLASH FLOODING. 
ACTIVITY NEAR THE SURFACE BOUNDARY -- ONCE IT ORGANIZES -- COULD
DROP SOUTH AND/OR BACKBUILD INTO NE PER 18Z GFS CORFIDI VECTORS
AND WHAT ONE WOULD EXPECT WITH AN INCREASE IN THE STRENGTH OF THE
LOW-LEVEL JET.  DESPITE FLASH FLOOD GUIDANCE VALUES OF AROUND 2.5
INCHES IN THREE HOURS, CELL TRAINING OVER 2-3 HOURS COULD LEAD TO
LOCAL AMOUNTS OF 3-6 INCHES, WHICH WILL LEAD TO FLASH FLOODING.

ROTH

ATTN...WFO...DVN...ARX...MPX...DMX...FSD...OAX...GID...LBF...

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

LAT...LON   41599996 43269845 44489629 44929390 44289229 41779214
            41919585 41599996