MESOSCALE PRECIPITATION DISCUSSION 0499
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
942 AM EDT THU JUL 28 2016
 
AREAS AFFECTED...TN AND OH VALLEY 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 281341Z - 281801Z
 
SUMMARY...ISOLATED FLASH FLOOD THREAT CONTINUES AS CONVECTION
MOVES OVER AREAS OF RELATIVELY LOW FLASH FLOOD GUIDANCE...

DISCUSSION...THE MID/UPPER LEVEL SHORTWAVE IS CURRENTLY SITUATED
ACROSS WESTERN TENNESSEE AS OF 13Z. VORTICITY HAS BEGUN TO BE
SHEARED OFF TO THE NORTHEAST AS WELL...WITH THE AXIS STRETCHING
FROM WESTERN TENNESSEE NORTHEASTWARD INTO SOUTHERN OHIO. MEANWHILE
AN UPPER JET STREAK MOVING ACROSS THE GREAT LAKES AND NEW ENGLAND
IS RESULTING IN A REGION OF DIVERGENT FLOW ACROSS PORTIONS OF THE
TN/OH VALLEYS AND THE MID ATLANTIC. BOTH OF THESE FEATURES ARE
RESULTING IN A FAVORABLE SETUP FOR ASCENT IN THE MID/UPPER LEVELS.

HAVE A SWATH OF VERY HIGH MOISTURE STRETCHING FROM THE LOWER MS
VALLEY NORTHEAST INTO THE OHIO VALLEY...WITH PRECIPITABLE WATER
VALUES ABOVE 2.2" ACROSS A PRETTY LARGE REGION. VALUES THIS HIGH
ARE NEAR RECORD VALUES FROM THE TN AND OH VALLEYS...WITH THESE
VERY ANOMALOUS VALUES MOVING INTO THE CENTRAL/NORTHERN MID
ATLANTIC THROUGH MORNING AS WELL. THE HIGH PWATS...HIGH WET BULB
ZERO HEIGHTS AND DEEP MOISTURE PROFILES SUPPORT EFFICIENT WARM
RAIN PROCESSES. MAIN LIMING FACTOR IS THE MARGINAL INSTABILITY
GIVEN CLOUD COVER AND WEAK LAPSE RATES. HOWEVER WILL LIKELY SEE
HEAVIER CONVECTIVE ELEMENTS EMBEDDED WITHIN THE BROADER STRATIFORM
RAIN AREA...ESPECIALLY ON THE LEADING EDGE OF
PRECIPITATION...WHERE SOME BREAKS IN THE CLOUDS SHOULD ALLOW FOR
LOCALLY HIGHER INSTABILITY. ALSO...MEAN FLOW IS PRETTY WELL
ALIGNED WITH THE MOISTURE AXIS AND PRECIPITATION SHIELD AS IT
SLOWLY MOVES EAST...SUPPORTING THE IDEA OF LOCALIZED TRAINING
ISSUES. 

THUS WHILE MOST OF THE RAIN SHIELD SHOULD HAVE RATES GENERALLY
BELOW A HALF INCH AN HOUR...EMBEDDED AMOUNTS OF 1-2" AN HOUR
APPEAR LIKELY ACROSS THE MPD AREA...WITH TOTALS LOCALLY AS HIGH AS
2-4" THROUGH 18Z. GIVEN THE LOW FLASH FLOOD GUIDANCE ACROSS THE
AREA...THESE AMOUNTS WILL LIKELY RESULT IN AN ISOLATED FLASH FLOOD
RISK THROUGH THE MORNING HOURS. OVERALL SEE THIS AS A MARGINAL
EVENT OVER THE NEXT SEVERAL HOURS...HOWEVER WILL CONTINUE TO
MONITOR TRENDS...AS THE THREAT COULD INCREASE BY THIS AFTERNOON AS
DAYTIME HEATING POTENTIALLY ALLOWS FOR GREATER DESTABILIZATION
AHEAD OF THE RAIN SHIELD AS IT PROGRESSES EAST.

CHENARD

ATTN...WFO...ILN...JKL...LMK...MEG...MRX...OHX...PAH...PBZ...
RLX...

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

LAT...LON   40518034 40177939 39247950 37878229 35648634 
            35468784 35828847 37658536 39428274 39898192 
            40188129