Mesoscale Precipitation Discussion 0635
NWS Weather Prediction Center College Park MD
302 PM EDT Sat Aug 11 2018

Areas affected...Southern Ohio, Northern Kentucky

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

Valid 111901Z - 112345Z

Summary...Thunderstorms were becoming more numerous along the Ohio
River between Ohio and Kentucky, and may begin to repeatedly
affect the same areas. This could produce flash flooding this
afternoon in parts of southern Ohio and northern Kentucky. Rain
rates may exceed 2 in/hr with the strongest storms.

Discussion...KILN radar showed a large cluster of thunderstorms
had become much more developed between 1730Z and 1900Z along the
Ohio River from near Maysville, KY to near Grayson, KY. This
convective cluster should lead to some training of thunderstorms
over at least the next couple hours, with the potential for flash
flooding. Additional scattered thunderstorms were beginning to
develop further northwest, closer to the Cincinnati metro area and
a surface low in southeast Indiana. If convective development
continues and focuses into the OH-KY border region, that may
exacerbate ongoing training trends and heighten the potential for
localized heavy rainfall.

Precipitable water values are above normal but not very anomalous,
around 1.5 to 1.6 inches per RAP analysis and CIRA blended PW
product. However, they are sufficiently high to support heavy rain
rates approaching (or briefly exceeding) 2 in/hr. The most
favorable ingredient for flash flooding is the potential for
training convection, and lengthening the duration of heavy rain at
a given location. As a shortwave trough begins to kick through the
area, mid-upper level winds will continue to veer, and the deep
layer mean wind should become increasingly aligned with the
current orientation of convection (roughly parallel with the Ohio
River). The highest chances of flash flooding appear to be in the
counties closest to the Ohio River on the OH-KY border, where FFG
also happens to be most reduced, particularly in Clermont and
Brown Counties in Ohio, and Pendleton, Bracken and Mason Counties
in Kentucky.

Lamers

ATTN...WFO...ILN...IND...JKL...LMK...RLX...

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

LAT...LON   39598503 39448356 38848194 38048201 37908310
            37978388 38778555