Mesoscale Precipitation Discussion 0640
NWS Weather Prediction Center College Park MD
723 PM EDT Thu Jul 10 2025

Areas affected...Northern IL and Southern WI

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

Valid 102322Z - 110522Z

SUMMARY...Increasing risk of flash flooding as coverage of
scattered thunderstorms expands along a warm front extending
across northern IL.

DISCUSSION...A warm front gradually lifting through northern
Illinois is providing a zone of surface convergence with
thunderstorms developing across eastern Iowa, northern Illinois,
and southern Wisconsin. MLCAPE values of 1500-2500 J/kg together
with a progressive, 500 mb trough swinging through will support
the maintenance of deep convection. Higher values of 0-6 km Bulk
Shear of 30-40 knots across eastern Iowa suggests that severe
convection may begin as discrete cells before growing upscale into
an MCS as the convection approaches the warm front. Meanwhile, a
simultaneous cluster of convection ongoing across northern
Illinois in a region of lower shear with slower storm motions is
likely to remain anchored along the warm front, posing a greater
flash flood risk.

Ample moisture with PW values ranging from 1.5-1.75" is in place
across the region, and CAMs guidance suggests an increasing risk
for convection along the warm front to backbuild and remain
quasi-stationary, particularly in extreme northern Illinois and
along the border with Wisconsin. HREF 6-hr QPF flash flood
guidance exceedance probabilities are 40-50% in that localized
region. Latest radar imagery also suggests that the cluster of
thunderstorms presently across north-central Illinois is beginning
to backbuild toward the west along the warm front, leading to the
likelihood of training convection for the next several hours. As
the separate area of convection across eastern Iowa moves toward
northern Illinois, the upscale growth of the resultant MCS will
further increase the likelihood of flash flooding.

Shieh

ATTN...WFO...ARX...DVN...LOT...MKX...

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

LAT...LON   43649099 43058915 42198778 41548772 41758919
            42079013 42559077 43119117