Mesoscale Precipitation Discussion 0815
NWS Weather Prediction Center College Park MD
328 PM EDT Sun Sep 09 2018

Areas affected...Easterm Kentucky, Far Southern Ohio, Western West
Virginia

Concerning...Heavy rainfall...Flash flooding possible

Valid 091926Z - 100030Z

Summary...Numerous thunderstorms and heavy rain bands were aligned
from near the Ohio-West Virginia border, southwest into central
Kentucky and Tennessee. This should set up repeating rounds of
heavy rain across much of eastern Kentucky and into West Virginia
this afternoon. Rain rates of 1-2 in/hr will be likely, and this
may lead to flash flooding in the complex terrain of the region.

Discussion...Regional radars showed a considerable amount of
convective activity stretching from near Charleston WV, southwest
along a surface cold front all the way to near Nashville TN and
beyond. Not every individual convective band was aligned with the
low-mid level mean wind, but collectively the ribbon of convection
was nearly parallel, and thus repeated rounds of heavy rain appear
likely from eastern Kentucky into West Virginia this afternoon.
The thunderstorms were increasing in coverage and intensity in a
corridor of moderate instability, with MLCAPE values around 1000
j/kg. This also overlapped with a plume of deep moisture, and
precipitable water values approaching 2 inches (per CIRA blended
TPW and GPS-PW observations). The highest PW values eastward
extent was limited by the Appalachian Mountains, as the column has
more limited depth due to the elevated terrain, but CIRA layer PW
product shows the plume of moisture above 700mb extends east to
nearly the WV-VA border region. The combination of deep moisture
and available instability should be sufficient to sustain ongoing
convection for at least another several hours. The 12Z HREF shows
a strong signal for heavy rainfall in western West Virginia, but
this may end up closer to the WV-KY border or perhaps into NE KY.
Stronger instability further south should support maintenance of
higher rain rates and there has been a slight northward bias to
the hi-res model QPF through much of this event. Nevertheless,
rain rates of 1-2 in/hr will be possible throughout the outlined
area, and this may lead to flash flooding in the complex terrain.

Lamers

ATTN...WFO...ILN...JKL...LMK...MRX...PBZ...RLX...

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

LAT...LON   39708177 39578080 38898063 37768154 36958292
            36718448 37168540 38478358