Mesoscale Precipitation Discussion 0802...Corrected
NWS Weather Prediction Center College Park MD
1013 AM EDT Sat Sep 08 2018

Corrected for a change in the header to "flash flooding likely"

Areas affected...southern IL into southern IN/northern
KY/southwestern OH

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

Valid 081358Z - 081900Z

SUMMARY...Flash flooding is expected across southern IL into
southwestern IN and northwestern KY with steady moderate to heavy
rain and 3-6 inch totals through 18Z. Lower totals of 1-3 inches
are forecast farther east into southeastern IN/southwestern
OH/northern KY on top of already low Flash Flood Guidance.

DISCUSSION...13Z surface observations placed a surface low just
southeast of Farmington, MO with a quasi-stationary front
extending to the east into central KY. RAOB data from and area VAD
wind plots showed an 850 mb front 75-150 miles to the north of the
surface front and the heaviest rain has been occurring between
these two boundaries. Recently, the heaviest rainfall rates across
the Ohio Valley had been located in southern IL and ranged between
0.5 and 1+ in/hr as of 1330Z. These rates were near surface
observations and KLSX and KVWX radar estimates, but are expected
to increase with some increases to instability forecast into the
early afternoon. Current/13Z instability was fairly weak across
southern IL with MLCAPE and MUCAPE estimates between 250 and 750
J/kg, which was between 12Z observed soundings from ILX, BNA and
ILN.

The greatest 850 mb moisture flux will occur just ahead of the
surface low (formerly T.D. Gordon) with 30-40 kt slowly shifting
east across the lower Ohio Valley, intersecting the 850 mb front
with an axis of strong convergence continuing from southern IL
into southern OH through 18Z. Better access to low level moisture
flux across southern IL/southwest IN supports the potential for
3-5 inches of rainfall, locally higher, through 18Z with pockets
of greater instability into OH supporting locally heavy rain with
rates 1-2 in/hr at times, but farther removed from the better
moisture flux to the west.

Otto

ATTN...WFO...ILN...ILX...IND...JKL...LMK...LSX...PAH...RLX...

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

LAT...LON   40078447 40068277 39708230 39218233 38658281
            38238421 38018609 37278763 37018879 37248939
            37928994 38558993 38908956 39278893 39758773
            39938580