MESOSCALE PRECIPITATION DISCUSSION 0138
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
634 PM EDT WED JUN 26 2013
 
AREAS AFFECTED......OHIO VALLEY... 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 262122Z - 270322Z
 
SUMMARY...1 TO 3-HOURLY RAINFALL RATES ARE EXPECTED TO EXCEED
FLASH FLOOD GUIDANCE ACROSS AN UNUSUALLY LARGE PORTION OF THE OHIO
VALLEY THROUGH THE EVENING.

DISCUSSION...AN ARRAY OF MESOSCALE DIAGNOSTICS...INCLUDING
MULTIPLE SATELLITE CHANNELS...RADAR...METARS...AND THE RAP
MODEL...SHOW THE EARLY TO MIDDLE STAGES OF A MESOSCALE CONVECTIVE
SYSTEM (MCS) CENTERED JUST NORTH OF CINCINNATI.  NUMEROUS TO
WIDESPREAD THUNDERSTORMS CONTINUE TO FORM ALONG AND AHEAD OF AN
ACCOMPANYING COLD FRONT OR OUTFLOW BOUNDARY THAT EXTENDS INTO
EXTREME NORTHERN KENTUCKY.  ADDITIONAL THUNDERSTORMS WERE FORMING
ALONG AND JUST NORTH OF RELATED OR NEARBY OUTFLOW BOUNDARIES
ACROSS PORTIONS OF SOUTHERN ILLINOIS AND SOUTHERN INDIANA IN AN
EXPANDING REGION OF ISENTROPIC UPGLIDE GENERATED ABOVE A GROWING
COLD POOL.  CELL MOTIONS AHEAD OF THE MCS WERE MORE
PROGRESSIVE...WHILE CELLS OVER PORTIONS OF ILLINOIS AND INDIANA
WERE PROPAGATING SLIGHTLY AGAINST THE MEAN LAYER FLOW...RESULTING
IN RAINFALL RATES OF 0.25 TO 0.75 INCHES AHEAD OF THE MCS AND 0.75
TO 2.0 INCHES BEHIND THE MCS RESPECTIVELY.  HOURLY RAINFALL RATES
IN EXCESS OF 1 INCH ARE SUFFICIENT TO EXCEED FFG
VALUE...PARTICULARLY ACROSS PORTIONS OF SOUTHERN ILLINOIS AND
SOUTHERN INDIANA.

SHORT-TERM HI-RESOLUTION NUMERICAL GUIDANCE APPEARS TO BE OF
LIMITED USE FOR THIS PARTICULAR EVENT...DUE IN PART TO THE RAPID
EVOLUTION OF THE MESOSCALE AND THAT THE HRRR MODEL HAS NOT BEEN
AVAILABLE SINCE 19Z.  THEREFORE...THE FORECAST IS LARGELY BASED ON
MESOANALYSIS AND SHORT-TERM EXTRAPOLATION.  THE MODEST COLD POOL
GENERATED WITHIN THE STRATIFORM REGION AND AN ACCOMPANYING REAR
INFLOW JET FAVOR CONTINUED STEADY PROGRESSION OF THE LEADING EDGE
OF THE MCS TOWARD THE EAST SOUTHEAST...IN ACCORDANCE WITH THE
AVERAGE CLOUD-LAYER WINDS AND 1000-500 THICKNESSES...GENERALLY
SUPPORTING HOURLY RAINFALL RATES BELOW 1 INCH ALONG ITS PATH. 
HOWEVER...RAINFALL RATES TOWARD THE REAR OF THE MCS...INCLUDING
PORTIONS OF SOUTHERN ILLINOIS AND SOUTHERN INDIANA...AND LATER
POSSIBLY INTO PORTIONS OF NORTHERN KENTUCKY...SHOULD CONTINUE
BETWEEN 0.75 AND 2.0 INCHES...DUE TO SLOWER STORM MOTION AND
TRAINING.  GIVEN THE ALREADY LOW FFG VALUES...THE PROBABILITY OF
EXCEEDING GUIDANCE IS ESTIMATED TO BE ABOUT 90 PERCENT.

JAMES

ATTN...WFO...RLX...JKL...ILN...LMK...IND...PAH...ILX...LSX...

ATTN...RFC...LMRFC...NCRFC...OHRFC...

LAT...LON   39568662 40218453 40248305 39658226 38728240 37718353
            37328530 37348693 37708900 38228985 38939021 39728998
            40068898 39568662