520
AWUS01 KWNH 140349
FFGMPD
MIZ000-INZ000-WIZ000-ILZ000-IAZ000-140700-

Mesoscale Precipitation Discussion 0616
NWS Weather Prediction Center College Park MD
1148 PM EDT Sat Jul 13 2024

Areas affected...northern Illinois

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

Valid 140347Z - 140700Z

Summary...A couple linear complexes are migrating
east-southeastward into northern Illinois.  Some concern exists
that stalling/training storms in some locales could result in an
increase in flash flood potential through 06Z.

Discussion...Mature linear complexes were migrating
east-southeastward into northern Illinois and were located along
an axis from 1) Waukegan to Rockford and 2) near Dubuque, IA.
These cells were persisting farther southeast than most
models/CAMs were depicting, but are being sustained by propagation
toward ~2500 J/kg MLCAPE and 25-kt southwesterly 850mb flow, which
was impinging on mature cold pools and helping to force continued,
strong updrafts.  The orientation of the MCSs (especially near
Rockford) are more suggestive of slower cell movement and training
(with motions more parallel to westerly flow aloft).  This could
eventually promote 1-2 inch/hr rain rates between Rockford and
western suburbs of Chicago between now and 06Z.  Additionally, a
second round of precipitation from the upstream linear segment
near Dubuque could produce another quick 0.5-1 inch of rainfall
across areas that experience training convection through 06Z.
FFGs are in the 1.5 inch/hr range across the discussion area, and
will be threatened in at least a few locales across the discussion
area through 06Z.

The overall scenario suggests an increase in flash flood potential
generally from Rockford through Chicago Metro in the next couple
hours.  The persistence of this threat is in question, however, as
weaker low-level flow/shear exists east of the IL/IN state line
and the linear segment moving in from the Dubuque area may act to
end the threat of most of the heavier rainfall as it migrates
through the discussion area through 06-07Z.  These trends will be
monitored for additional flash flood potential beyond 06Z.

Cook

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

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

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

LAT...LON   43068895 42398683 41468670 41218750 41218819
            41589009 42819061