AWUS01 KWNH 150902
FFGMPD
OHZ000-INZ000-ILZ000-MOZ000-IAZ000-151500-

Mesoscale Precipitation Discussion 1059
NWS Weather Prediction Center College Park MD
500 AM EDT Sat Aug 15 2026

Areas affected...Southeast IA...Northeast MO...Central and
Northern IL...Central and Northern IN...Far Western OH

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

Valid 150900Z - 151500Z

SUMMARY...Widespread shower and thunderstorm activity with locally
extreme rainfall rates will continue this morning. Numerous to
widespread areas of flash flooding including areas of high-end and life-threatening impacts are expected.

DISCUSSION...The latest GOES-E IR satellite imagery shows a strong
west/east oriented MCS advancing across sizable areas of the
Midwest. The coldest convective tops (-75 to -80 celsius) are
depicted over far southeast IA through western and central IL.
MRMS data shows extremely heavy showers and thunderstorms with
rainfall rates occasionally into the 2 to 3+ inch/hour range.

All of the convective activity continues to advance east along a
strong elevated instability gradient situated north of a
quasi-stationary front draped from northern MO eastward across
southern IL and adjacent areas of the Lower OH Valley.

MUCAPE values of 1500 to 2500 J/kg are in place, with extremely
high PWs of 2.2 to 2.4+ inches based on the latest RAP analysis
and GPS-derived data. Earlier RAOB soundings from 00Z confirmed
deep WCD layers and an environment conducive for extremely
efficient convection with high-end rainfall rates.

This will continue to be supported through early this morning by
the nose of a southwest low-level jet of 30 to 40+ kts overrunning
the front. This will sustain enhanced isentropic ascent/forcing
while promoting downstream moisture and instability transport. An
MCV also remains embedded within the larger scale convective mass
across southeast IA, and this coupled with the favorable
thermodynamic and kinematic environment will favor convective
sustenance for several more hours.

Numerous to widespread areas of flash flooding are already
occurring across far southeast IA through western and central IL.
This threat is expected to extend downstream this morning across
eastern IL and much of central IN. By late this morning, areas of
western OH may also begin to be impacted. Low FFG values and high
streamflows per USGS data are noted all across these areas, and
thus the antecedent conditions are very sensitive.

The latest model guidance supports additional rainfall amounts
through this morning as high as 3 to 6+ inches, and especially
with strong cell-training concerns. Given the antecedent
environment, and high rainfall potential over multiple major
metropolitan areas, high-end and life-threatening flash flooding
impacts are expected.

Orrison

ATTN...WFO...DMX...DVN...EAX...ILN...ILX...IND...IWX...LOT...LSX...

ATTN...RFC...KRF...MSR...TIR...NWC...

LAT...LON 41698779 41568653 41298518 40888458 40358443
39828470 39458538 39258700 39418922 39589088
39869256 40119327 40649367 41189329 41449196
41648996

$$
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