Mesoscale Precipitation Discussion 0867
NWS Weather Prediction Center College Park MD
1246 AM EDT Sat Aug 05 2023

Areas affected...Western Illinois

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

Valid 050444Z - 051000Z

SUMMARY...Swath of heavy rain and flash flooding to continue
drifting east from northern Missouri into western Illinois into
the overnight. Rainfall rates of 2 to 3 inches per hour should
overcome the progressively drier antecedent conditions to the east
into Illinois, so flash flooding is considered likely.

DISCUSSION...Regional NEXRAD denotes a well defined swath of heavy
rain ahead of an MCV/Shortwave and north of a surface low across
northeastern MO which is slowly drifting east. Maintenance of this
convergent swath is expected into western IL as southeasterly low
level inflow brings some drier and unstable air from southern IL
on top of high moisture under this MCV and south through eastern
MO with PW of 2 to 2.2".

The deeper moisture intersection near the surface low and
northward should continue to have ample narrow skinny CAPE for
strong updrafts and moisture flux for 2-3"/hr rates into or
through the rest of the overnight. Slow, nearly due eastward
progression of the MCV/surface wave should keep orientation of
some cells to align favorably for longer duration and support a
swath of highest rainfall totals of 3 to 5" with locally 6"
possible.

Western IL has generally missed all the heavy rain that central
and eastern MO has received over the past several days, so FFG
greatly increases east into IL to generally around 3"/3hr.
However, given the slow motion and highly efficient rainfall of
longer than an hour duration, flash flooding is considered likely
through 10Z.


Jackson

ATTN...WFO...DVN...ILX...LSX...

ATTN...RFC...NCRFC...NWC...

LAT...LON   40689115 40679006 40418947 39888943 39438987
            39299060 39599128 39879216 40409233 40539177