MESOSCALE PRECIPITATION DISCUSSION 0295
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1218 AM EDT TUE AUG 19 2014
 
AREAS AFFECTED...PORTIONS OF WI AND WESTERN LOWER MI 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 190418Z - 190848Z
 
SUMMARY...A BROAD THUNDERSTORM AREA WITH A LEADING WAA
THUNDERSTORM BAND IS EXPECTED TO CONTINUE MOVING EASTWARD ACROSS
WI, WITH HOURLY RAIN RATES UP TO 2".  FLASH FLOODING IS POSSIBLE
HERE.

DISCUSSION...A FRONTAL WAVE NEAR THE CENTRAL MN/WI BORDER
COMBINING WITH AN OUTFLOW BOUNDARY GENERALLY WITHIN ITS WARM
SECTOR ARE LEADING TO A BROAD AREA OF SHOWERS AND THUNDERSTORMS,
WITH THE NORTHEAST EDGE OF THE HEAVY RAINFALL WITHIN ~100 MILES
NORTHEAST OF A POOL OF 1000+ J/KG CAPE WHICH LIES ACROSS SOUTHEAST
MN, SOUTHERN WI, AND SOUTHWESTERN MI.  WHILE THE SYSTEM IS
GENERALLY PROGRESSIVE, A SHORT WARM AIR ADVECTION THUNDERSTORM
BAND HAS FORMED POLEWARD OF THE WARM FRONT, WHICH AMPLIFIES THE
FLASH FLOOD RISK.  RADAR ESTIMATES OF THE RECENT HOURLY RAIN RATES
ARE CLOSE TO 2.5", THOUGH SOME HAIL WAS LIKELY AMPLIFYING THOSE
TOTALS ABOVE REALITY.  INFLOW AT 850 HPA IS IN THE 25-30 KNOT
RANGE, AND PRECIPITABLE WATER VALUES OF 1.75" LIE WITHIN THE
REGION.  THE CRITERIA FOR THE WET MULTICELL ENVIRONMENT HAVE BEEN
REACHED.

THE EXPECTATION IS THAT THE SYSTEM SHOULD REMAIN PROGRESSIVE, WITH
A PRECEDING WARM ADVECTION BAND OF THUNDERSTORMS CONTINUING CELL
TRAINING NORTH OF THE WARM FRONT.  A SLIGHT INCREASE IN 850 HPA
INFLOW WITHIN THE NEXT FEW HOURS COULD CAUSE SOME TEMPORARY
BACKBUILDING.  THUNDERSTORMS SHOULD FADE AS THEY MOVE INTO CENTRAL
LOWER MI ONCE THEY MOVE FAR ENOUGH FROM THE INSTABILITY REGION. 
HOURLY RAIN RATES OF UP TO 2", WITH LOCAL AMOUNTS OF 3-5" PER THE
MOST RECENT MESOSCALE GUIDANCE, COULD LEAD TO FLASH FLOODING.

ROTH

ATTN...WFO...APX...ARX...DLH...DMX...DVN...GRB...GRR...LOT...

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

LAT...LON   45719027 44988788 44428643 43878527 43288465 
            42468510 42408703 42568951 42759255 42809269 
            42949372 43179231 43679081 44229084 45419168