Mesoscale Precipitation Discussion 0812
NWS Weather Prediction Center College Park MD
1043 AM EDT Sun Sep 09 2018

Areas affected...Eastern Kentucky, Southern Ohio, Western West
Virginia

Concerning...Heavy rainfall...Flash flooding likely

Valid 091442Z - 091940Z

Summary...Heavy rain bands and thunderstorms are expected to
continue into the early afternoon in the vicinity of a surface low
and slow-moving fronts in the middle Ohio River Valley. In
particular, the heavier rain bands may focus in the next few hours
near a warm front from northeast Kentucky into the Ohio-West
Virginia border region. Rain rates may approach 2 in/hr in
localized bands, which could lead to flash flooding. Elsewhere,
rain rates should be lower, but additional rain falling on
saturated soil could prolong existing areas of flooding.

Discussion...Based on surface observations, a surface low was
situated very close to Lexington KY at 14Z, with a warm front
extending east just south of I-64 and curling back to the
southeast near the KY-WV border. The warm front was quite
pronounced; for example the temperature difference between
Prestonsburg (KSJS, 79F) and Huntington (KHTS, 66F) was over 10
degrees in about 40 miles. Convective rain bands and even some
thunderstorms were focusing in the general vicinity of the warm
front, and the RAP suggests this will continue into the early
afternoon -- perhaps enhanced by differential heating with the
warm sector relatively cloud free at the moment. Instability
should also continue to build in the warm sector, giving the
convective bands access to southerly inflow from an increasingly
unstable air mass. This may allow the intensity of the convection
to increase between 15Z and 17Z in some areas, and perhaps
extending south along the cold front into other portions of
eastern and central Kentucky.

Of particular concern is the area in the immediate vicinity of
I-64 in northeast Kentucky. Average storm motions are to the
northeast (from approx 225-230 degrees), which is very close to
the orientation of the deep layer mean wind vectors and the
sharpening surface front. This may allow for a more focused area
of training convection, heavy rainfall, and flash flooding. Flash
flood guidance is also substantially reduced in this confined area
of northeast Kentucky due to antecedent heavy rainfall, which
should further enhance the flash flood risk. The region of concern
is from near Richmond KY northeast to near Huntington WV, and
roughly 30-40 miles either side of that line. Additional flash
flooding will be possible with any convective bands that can
develop in the warm sector, or build into the western portions of
West Virginia.

North of the warm front, flash flood guidance is also
significantly reduced due to overnight heavy rainfall, and there
have been numerous reports of ongoing areal flooding this morning
into southern Ohio. Although this area is more stable at the
present time, some hi-res models show heavier rain rates
redeveloping north and northwest of the surface low and warm front
into the early afternoon. Even if that does not occur, any
additional light to moderate rain should allow ongoing widespread
areal flooding to continue.

Lamers

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

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

LAT...LON   39598225 38808091 37678233 36918395 36708485
            36968594 37848575 39398378