424
AWUS01 KWNH 100654
FFGMPD
OHZ000-MIZ000-INZ000-WIZ000-ILZ000-101230-

Mesoscale Precipitation Discussion 0994
NWS Weather Prediction Center College Park MD
252 AM EDT Mon Aug 10 2026

Areas affected...Lower Great Lakes

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

Valid 100651Z - 101230Z

Summary...Thunderstorms with hourly rainfall as high as 2.5" will
continue to spread across the lower Great Lakes into the early
morning. Where any repeating/training can occur, total rainfall of
3-5" is possible. This may result in additional flash flooding.

Discussion...The GOES-E IR imagery early this morning shows an
impressive MCS with a large area of -50C or colder cloud tops
moving over northeast Illinois and into Indiana/Michigan. Embedded
even colder cloud tops are indicative of still deepening
convection, which is additionally reflected by the regional radar
mosaic featuring many clusters of thunderstorms moving across the
area.

This activity is building within an area of strong overlapping
deep layer ascent caused via a mid-level shortwave moving atop a
stationary front and isentropic upglide on a 30-40kt 850mb LLJ.
This LLJ is gradually strengthening as noted via regional VWPs,
and is transporting robust thermodynamics (PWs above 2" and MUCAPE
of 3000-4000 J/kg) northeastward. The deep layer lift impinging
into these thermodynamics will continue to fuel convective
development, and recent MRMS hourly rainfall has already exceeded
2 inches in the strongest cores.

There is high confidence that thunderstorms will continue into the
morning, although the footprint of heaviest rainfall continues to
be somewhat uncertain. The high-res CAMs are all in agreement that
stripes of heavy rainfall will occur both just north of the front
where an MCV tracking across Lake Michigan will locally accelerate
inflow to enhance the isentropic upglide, as well from northeast
Illinois into northwest Indiana where the most impressive moisture
flux occurs on the LLJ convergence. With rainfall rates climbing
above 2"/hr within the deeper convection, any repeating cells or
training of heavy rain could create 3-5" of rain with locally
higher amounts (5-10% chance for more than 5 inches according to
both HREF and REFS).

There is a slightly higher risk of the heaviest rain occurring
across IL/IN than in lower MI due to a higher training potential,
but much of this region is already vulnerable from recent heavy
rainfall and compromised FFG. While there continues to be some
uncertainty as to whether the additional heavy rain can
efficiently overlap recent rain footprints (and accompanying
reduced FFG) anywhere these intense rain rates can train or
repeat, a flash flood risk will exist.


Weiss

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...DTX...DVN...GRR...ILN...ILX...IND...IWX...LOT...
MKX...

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

LAT...LON   43388619 43288462 42328374 41248414 40558499
            40388538 40188600 40338745 40728868 41338920
            42388859 43078784