MESOSCALE PRECIPITATION DISCUSSION 0132
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 PM EDT TUE JUN 25 2013
 
AREAS AFFECTED...NORTHEAST IN...SOUTHERN MI...NORTHERN AND CENTRAL
OH...WESTERN PA...NORTHERN WV 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 260300Z - 260600Z
 
SUMMARY...A CONVECTIVE BAND IS BROADENING AS IT DROPS
EAST-SOUTHEAST FROM THE SOUTHERN MICHIGAN INTO THE UPPER OHIO
VALLEY.  A QUICK 2-3" OF RAIN COULD CAUSE FLASH FLOODING.

DISCUSSION...THE 02Z MESOANALYSIS REVEALS A WAVY BAROCLINIC BAND,
COMPOSED OF TWO WAVES OF LOW PRESSURE ACROSS NORTHEAST IN AND NEAR
DETROIT MI.  PER THE 12Z ARW GUIDANCE AND RECENT RADAR IMAGERY,
CONVECTION IS CURRENTLY INITIATED NEAR A SURFACE BOUNDARY -- THEN
MOVES DOWNSTREAM WITHIN THE MEAN-LAYERED FLOW -- AS CIN IS
MINIMAL. THE 850-250 MEAN FLOW IN THIS REGION IS TOWARDS THE
EAST-SOUTHEAST, AND RECENT RADAR TRENDS INDICATE SOME SOUTHWARD
COMPONENT TO MOTION AND SOME REORIENTATION OF THE CONVECTIVE BAND
TOWARDS A WEST- NORTHWEST/ EAST- SOUTHEAST AXIS. THERE IS SOME
RECENT EVIDENCE OF BACKBUILDING OF THUNDERSTORM ACTIVITY ACROSS
SOUTHERN LAKE MICHIGAN ON RADAR IMAGERY, WHICH INDICATES THE
RAINFALL IS NOT QUITE OVER ACROSS SOUTHERN MI.  SATELLITE-BASED
CAPE VALUES ARE AROUND 3000 J/KG ACROSS OH, ADVERTISING PLENTY OF
INSTABILITY.  INFLOW AT THE 850 HPA LEVEL IS OUT OF THE WEST,
INDICATING THAT NEW CONVECTION ACROSS CENTRAL IL IS HAVING MINIMAL
IMPACT ON INFLOW INTO THIS THUNDERSTORM BAND.  PRECIPITABLE WATER
VALUES ARE 1.75-2 INCHES, INDICATING THE SYSTEM HAS SIGNIFICANT
AMOUNTS OF MOISTURE TO WORK WITH.  THE REGION IS DIVERGENT ALOFT
SOUTHEAST OF A SHORTWAVE MOVING THROUGH WI.

AS THE CONVECTIVE BAND BEGAN TO ORGANIZE AROUND 1Z/9 PM EDT, IT IS
POSSIBLE THAT AN ARCED CONVECTIVE BAND/SQUALL LINE ATTEMPT MAY
DROP OUT OF THIS REGION AROUND 5-6Z/1-2 AM EDT, WHICH COULD
MINIMIZE THE FLASH FLOOD THREAT LATE IN THE PERIOD.  HOWEVER, A
RECENT ARCED BAND OF THUNDERSTORMS HAS MOVED THROUGH THE EASTERN
OH, SOUTHWEST PA, AND THE NORTHERN TIP OF WV WHICH SHOULD HAVE
LOWERED FLASH FLOOD GUIDANCE VALUES TO ROUGHLY 2 INCHES IN 3
HOURS.  SINCE THE EXPECTATION IS FOR 2-3 INCHES OF RAIN TO FALL IN
A SHORT TIME FRAME -- PER ESTIMATES OF RAINFALL ACROSS SOUTHERN MI
-- BELIEVE FLASH FLOODING IS POSSIBLE OVER THE NEXT FEW HOURS.

ROTH

ATTN...WFO...CTP...PBZ...RLX...CLE...ILN...DTX...IWX...GRR...
LOT...

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

LAT...LON   40108435 40858589 41638694 42228661 42488550 42368305
            41798076 41017939 39887919 39108042 39398232 40068424
            40108435