MESOSCALE PRECIPITATION DISCUSSION 0360
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
253 AM EDT THU JUN 22 2017

AREAS AFFECTED...SOUTHEAST MN & CENTRAL WI

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

VALID 220652Z - 221252Z

SUMMARY...THUNDERSTORMS CONTINUE TO FORM OVER PORTIONS OF IA AND
WESTERN WI.  HOURLY RAIN RATES TO 1.75", WITH LOCAL AMOUNTS TO 3",
ARE EXPECTED.

DISCUSSION...A MESOSCALE WAVE HAS BEEN SPAWNED ACROSS SOUTHERNMOST
MN AHEAD OF AN OUTFLOW BOUNDARY FROM CONVECTION WHICH FORMED
PREVIOUSLY ALONG THE IA/MN BORDER, WHICH HAD LED TO NEW
THUNDERSTORM ACTIVITY IN NORTHEAST IA NEAR A WARM FRONT THAT IS
MOVING EAST-SOUTHEAST.  OTHER NEWER ACTIVITY IS FORMING ALONG AN
INVERTED TROUGH WITHIN THE COLD SECTOR OF THE SYSTEM.  DIVERGENCE
ALOFT IS BEING AIDED BY A SHORTWAVE MOVING ACROSS NORTHWEST MN.  A
RELIABLE GPS PRECIPITABLE WATER VALUE OF 1.57" CAME IN RECENTLY
FROM THIS AREA.  MUCAPE VALUES ARE 1000-2000 J/KG, WHICH ARE BEING
WHISKED ACROSS THE AREA BY 850 HPA INFLOW OF ~50 KTS PER UPSTREAM
VAD WIND PROFILES, BARELY EXCEEDING THE MEAN 850-400 HPA WIND. 
EFFECTIVE BULK SHEAR IS QUITE HIGH, NEAR 60 KTS PER THE MOST
RECENT SPC MESOANALYSIS.

CONSIDERING THE DEGREE OF BULK SHEAR AND INSTABILITY AVAILABLE,
MESOCYCLONES ARE POSSIBLE IN THIS ENVIRONMENT.  INCREASED
CONVECTIVE GROWTH/COVERAGE IS EXPECTED WITH TIME.  NEARLY
UNIDIRECTIONAL FLOW WITH HEIGHT SHOULD LEAD TO OCCASIONAL CELL
TRAINING, AND THERE IS THE CHANCE THAT THE MORE NORTHERN ACTIVITY
COULD MERGE WITH ACTIVITY FARTHER SOUTH WITH TIME.  THE 18Z SSEO
NEIGHBORHOOD PROBABILITIES ADVERTISE THAT 10Z IS AROUND THE PEAK
TIME FOR THIS ACTIVITY FROM A RAINFALL EFFICIENCY STANDPOINT,
PARTICULARLY ACROSS WI.  SOUTH-CENTRAL WI IS FORECAST TO HAVE THE
LONGEST PERIOD OF PERSISTENT LOW-LEVEL INFLOW AND HIGHEST MOISTURE
VALUES.  THE BIGGEST ISSUE FROM A HEAVY RAIN PERSPECTIVE IS
FORWARD PROPAGATION, WHICH IS EXPECTED TO DIRECT STORMS TO THE
EAST TO EAST-SOUTHEAST AT ~30 KTS. 

ADDING TO THE UNCERTAINTY IS THE POOR HANDLE ON THIS ACTIVITY BY
THE MESOSCALE GUIDANCE.  THE 00Z NAM CONEST, 00Z SPC WRF, AND 00Z
WRF NSSL APPEAR TO BE HANDLING THIS ACTIVITY BETTER THAN THE OTHER
GUIDANCE AT THE MOMENT, THOUGH THEY APPEAR TOO FAR TO THE NORTH IN
PLACEMENT AND MAY NOT BE BROAD ENOUGH IN COVERAGE.  HOURLY RAIN
RATES TO 1.75" WITH LOCAL AMOUNTS TO 3" ARE EXPECTED, WHICH COULD
BREACH THE MODEST FLASH FLOOD GUIDANCE IN THIS REGION.

ROTH

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

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

LAT...LON   44809045 44488773 43718765 43108808 42428928
            41959095 41809282 42689414 43679469 44469267