MESOSCALE PRECIPITATION DISCUSSION 0119
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
400 PM EDT SUN APR 16 2017

AREAS AFFECTED...SOUTHERN IL, WESTERN & SOUTHERN KY

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

VALID 161959Z - 162359Z

SUMMARY...THUNDERSTORMS ARE INCREASING IN COVERAGE NEAR AND SOUTH
OF THE OHIO RIVER.  WITH HOURLY RAIN RATES UP TO 1.75", AND LOCAL
AMOUNTS OF 2-4", FLASH FLOODING IS CONSIDERED POSSIBLE.

DISCUSSION...SATELLITE AND RADAR IMAGERY SHOW INCREASING
CONVECTIVE COVERAGE FROM THE CONFLUENCE OF THE OH/MS RIVERS
EASTWARD INTO THE LOWER OH VALLEY AHEAD OF AN INCOMING MCV. 
PRECIPITABLE WATER VALUES ARE ~1.5" IN THE REGION.  INFLOW AT 850
HPA IS ~25 KTS OUT OF THE WEST-SOUTHWEST, JUST EXCEEDING THE MEAN
850-400 HPA WIND. THE FLOW IS NEARLY UNIDIRECTIONAL, AND MLCAPES
OF 1000-1500 J/KG LIE ACROSS WESTERN KY.  BULK SHEAR IN THE 0-6 KM
LAYER IS AROUND 25 KTS, ENOUGH TO CAUSE SOME CONVECTIVE
ORGANIZATION.  AN OUTFLOW BOUNDARY ACROSS NORTH-CENTRAL KY IS
SLOWLY SINKING SOUTHWARD.

THE GUIDANCE SUGGESTS THAT AS THE INSTABILITY GROWS ANOTHER ~500
J/KG BETWEEN NOW AND SUNSET THAT CONVECTIVE COVERAGE SHOULD GROW
FURTHER.  PRECIPITABLE WATER VALUES SHOULD SLIGHTLY INCREASE AS
WELL.  FOR PLACEMENT, THE 12Z SPCWRF AND A SLIGHTLY EXPANDED 12Z
GFS APPEAR BEST OVER THE NEXT SEVERAL HOURS.  MUCH OF THE GUIDANCE
APPEARS TO BE SLIGHTLY UNDERSELLING THE POTENTIAL HERE,
AMOUNT-WISE.  CELL TRAINING AHEAD OF THE MESOSCALE WAVE APPEARS TO
BE THE MAIN HEAVY RAIN THREAT.  PROPAGATION IS EXPECTED TO THE
EAST-SOUTHEAST AT 15-20 KTS AS THE NORTHERN EDGE OF THE
INSTABILITY POOL IS SLOWLY CARVED AWAY BY ONGOING CONVECTION. 
HOURLY RAIN RATES UP TO 1.75", WITH LOCAL AMOUNTS OF 2-4", COULD
EXCEED THE ~3" IN THREE HOUR FLASH FLOOD GUIDANCE VALUES.

ROTH

ATTN...WFO...JKL...LMK...PAH...

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

LAT...LON   38358449 37958380 37258506 36928630 36798766
            36999014 37608952 38108723 38238554