Alert archive / Illinois / Mesoscale Discussions in 2026

Mesoscale Discussion 1921

August 11, 20264 states

The Storm Prediction Center issued this mesoscale discussion at Aug 11, 2026, 9:00 AM CDT for 4 states. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Aug 11, 2026, 9:00 AM CDT (14:00 UTC)
Expired
Aug 11, 2026, 11:00 AM CDT
In force
2 hr
Issued by
the Storm Prediction Center
Concerning
Severe thunderstorm watch 563
All 49 counties

Cedar County, IA, Clinton County, IA, Dubuque County, IA, Jackson County, IA, Jones County, IA, Muscatine County, IA, Scott County, IA, Boone County, IL, Bureau County, IL, Carroll County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Ford County, IL, Grundy County, IL, Henry County, IL, Iroquois County, IL, Jo Daviess County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Knox County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Marshall County, IL, McHenry County, IL, McLean County, IL, Mercer County, IL, Ogle County, IL, Peoria County, IL, Putnam County, IL, Rock Island County, IL, Stark County, IL, Stephenson County, IL, Whiteside County, IL, Will County, IL, Winnebago County, IL, Woodford County, IL, Lake County, IN, Newton County, IN, Grant County, WI, Green County, WI, Iowa County, WI, Kenosha County, WI, Lafayette County, WI, Rock County, WI, Walworth County, WI

The radar

The Chicago radar (KLOT), 91 km from the middle of the area, began a volume at 14:01 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Davenport, (KDVN), launched 12:00Z, 2.0 hours before the alert went out and 111 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-pSkew-T log-p diagram, Davenport, at 12:00Z on 2026-08-11Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 4268 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Davenport, at 12:00Z on 2026-08-11The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 136 square meters per square second.19395878Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
4268 J/kg
Mixed-layer CIN
-76 J/kg
Mixed-layer LCL
891 m above ground
0-6 km bulk shear
38 kt
0-1 km storm-relative helicity
136 m²/s²
0-3 km storm-relative helicity
153 m²/s²
Significant tornado parameter
2.1
Supercell composite
9.5

Open this sounding in Storm Lab

The text

As transmitted.

423 
ACUS11 KWNS 111401
SWOMCD
SPC MCD 111400 
INZ000-ILZ000-WIZ000-IAZ000-111600-

Mesoscale Discussion 1921
NWS Storm Prediction Center Norman OK
0900 AM CDT Tue Aug 11 2026

Areas affected...southern Wisconsin...northern Illinois...and far
northwest Indiana

Concerning...Severe Thunderstorm Watch 563...

Valid 111400Z - 111600Z

The severe weather threat for Severe Thunderstorm Watch 563
continues.

SUMMARY...The potential for significant wind gusts up to 75-85 mph
is expected to persist with an evolving bow echo this morning.

DISCUSSION...An MCS with a history of producing wind gusts of 70-80
mph is currently evolving into a broader bowing configuration over
east-central IA and far northwest IL as of 1355Z. The 12z DVN
sounding is likely a good representation of the ambient inflow
environment, featuring steep mid-level lapse rates and abundant
boundary-layer moisture, yielding MUCAPE of 4500-5000 J/kg. A
largely unidirectional wind profile with around 35 kt of deep-layer
shear (per the 12z DVN sounding and current VWP) in conjunction with
the strongly unstable environment is likely to support further
intensification of the bow echo with an associated risk for
significant wind gusts up to 75-85 mph. Around 30 kt of 0-3 km shear
oriented largely perpendicular to the cold pool may support some
tornado potential, especially where the low-level shear and cold
pool remain in balance. 

The bow echo is expected to track along a residual outflow boundary
from a downstream MCS, which extends east-southeast through the
south side of the greater Chicago metropolitan area into far
northwest IN.

..Mead.. 08/11/2026

...Please see www.spc.noaa.gov for graphic product...

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

LAT...LON   41019100 41759134 42869123 43259046 42988895 42728791
            42168727 41348703 40718724 40268791 40358868 41019100 

MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Aug 10, 9:07 PM CDTMesoscale DiscussionSPCBoone, Carroll, Jo Daviess, Lee, Ogle, Stephenson and 2 more113 min
Aug 11, 7:22 AM CDTSevere Thunderstorm WatchSPCBoone, Bureau, Carroll, Champaign, Cook, DeKalb and 32 more6 hr
Aug 11, 2:28 PM CDTMesoscale DiscussionSPCChampaign, Douglas, Edgar, Vermilion2 hr
Aug 11, 5:24 PM CDTMesoscale DiscussionSPCClark, Crawford2 hr
Aug 10, 8:00 PM CDTMesoscale DiscussionSPCAdams, Allen, Blackford, Cass, DeKalb, Elkhart and 16 more90 min
Aug 11, 7:00 AM CDTMesoscale DiscussionSPCDelaware, Henry, Randolph, Union, Wayne2 hr
Aug 11, 7:41 AM CDTSevere Thunderstorm WatchSPCDearborn, Fayette, Franklin, Henry, Ohio, Rush and 3 more7 hr
Aug 11, 9:31 AM CDTMesoscale DiscussionSPCAdams, Allen, Blackford, Boone, Carroll, Cass and 29 more119 min
Aug 11, 10:01 AM CDTSevere Thunderstorm WatchSPCAdams, Allen, Bartholomew, Blackford, Boone, Brown and 57 more10 hr
Aug 11, 10:18 AM CDTMesoscale DiscussionSPCDearborn, Ohio117 min
Aug 11, 11:12 AM CDTMesoscale DiscussionSPCFranklin, Union, Wayne63 min
Aug 11, 11:40 AM CDTSevere Thunderstorm WatchSPCFayette, Franklin, Union, Wayne7 hr
Aug 11, 11:42 AM CDTMesoscale DiscussionSPCAllen, Benton, Blackford, Boone, Carroll, Cass and 29 more2 hr
Aug 11, 12:57 PM CDTMesoscale DiscussionSPCBoone, Clinton, Dearborn, Decatur, Delaware, Fayette and 15 more2 hr
Aug 11, 1:36 PM CDTSevere Thunderstorm WatchSPCClark, Crawford, Dearborn, Dubois, Floyd, Harrison and 8 more7 hr
Aug 11, 2:52 PM CDTMesoscale DiscussionSPCDearborn, Ohio, Ripley, Switzerland113 min
Aug 11, 1:15 AM CDTMesoscale DiscussionSPCCherokee, Clay, Dickinson, Lyon, O'Brien, Osceola and 2 more2 hr
Aug 11, 4:13 AM CDTMesoscale DiscussionSPCBenton, Black Hawk, Boone, Bremer, Buchanan, Buena Vista and 33 more2 hr

Nearby

Mesoscale Discussions in Illinois, 2026Mesoscale Discussions in Iowa, 2026Mesoscale Discussions in Wisconsin, 2026Every mesoscale discussion in 2026

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.