MESOSCALE PRECIPITATION DISCUSSION 0497
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1034 PM EDT FRI JUL 20 2018

AREAS AFFECTED...PORTIONS OF THE MID-SOUTH

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

VALID 210233Z - 210833Z

SUMMARY...SIGNIFICANT INSTABILITY INTERACTING WITH A NORTH-SOUTH
ORIENTED OUTFLOW BOUNDARY IS EXPECTED TO CONTINUE HEAVY RAIN
ISSUES IN THE MID-SOUTH.

DISCUSSION...SHOWERS AND THUNDERSTORMS ARE BEGINNING TO FILL IN
BETWEEN TWO BANDS OF HEAVY RAINFALL ACROSS NORTHERN KY AND EASTERN
TN.  CONVERGENT 850 HPA INFLOW OF 30-50 KTS IS IMPORTING 2000-4000
J/KG OF MU CAPE INTO A NORTH-SOUTH OUTFLOW BOUNDARY WITHIN A
DIVERGENT AREA ALOFT SOUTH OF AN UPPER LOW OVER NORTHERN LAKE
MICHIGAN.  PRECIPITABLE WATER VALUES IN THE AREA ARE 1.5-1.9" PER
GPS DATA AND NASHVILLE'S 00Z SOUNDING.  EFFECTIVE BULK SHEAR IN
THE REGION IS 30-50 KTS, HIGH ENOUGH TO BE WORRIED ABOUT
MESOCYCLONE FORMATION.

PORTIONS OF THE AREA HAVE RECEIVED 3-5" OF RAINFALL TODAY, WHICH
POTENTIALLY UPS THE ANTE ON FLASH FLOODING.  AS CIN HAS SET IN,
THUNDERSTORMS WITH HEAVY RAINFALL COULD FALL ON SOME OF THESE
SATURATED SOILS AS FORWARD PROPAGATING CONVECTIVE VECTORS BECOME
MORE WEST TO EAST OVERNIGHT.  THE BETTER 850 HPA CONVERGENCE
SLOWLY SHIFTS FROM NORTH TO SOUTH THROUGH TN AND KY THROUGH 09Z
WHILE THE LOW-LEVEL FOCUS SHIFTS FROM EAST TO WEST AS THE COLD
POOL BECOMES LARGER FROM ONGOING CONVECTION, ERODING THE
INSTABILITY POOL FROM THE EAST.  THE AVAILABLE MOISTURE AND
INSTABILITY SUPPORT HOURLY RAIN TOTALS TO 2".  THE MESOSCALE
GUIDANCE HAS A GOOD SIGNAL FOR LOCAL AMOUNTS IN THE 3-4" RANGE. 
ISSUES WOULD BE MOST SIGNIFICANT IN URBAN AREAS AND OVER
SATURATING SOILS. 

SINCE THE OVERLAP BETWEEN THE EXPECTED HEAVY RAINFALL AND WHAT HAS
FALLEN SO FAR IS UNCLEAR, HAVE LEFT THE CATEGORY AS POSSIBLE.
 
ROTH

ATTN...WFO...BMX...FFC...GSP...HUN...ILN...JKL...LMK...MRX...
OHX...PAH...

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

LAT...LON   38498461 37568337 35568390 34688443 34478481
            34368568 34998665 36298725 37898787 38118621