Alert archive / Illinois / Mesoscale Discussions in 2026

Mesoscale Discussion 484

April 17, 202628 counties in Illinois; Clark County, Missouri

The Storm Prediction Center issued this mesoscale discussion at Apr 17, 2026, 6:25 PM CDT for 28 counties in Illinois; Clark County, Missouri. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued
Apr 17, 2026, 6:25 PM CDT (23:25 UTC)
Expired
Apr 17, 2026, 8:30 PM CDT
In force
2 hr
Issued by
the Storm Prediction Center
Concerning
Tornado watch 129...131
All 29 counties

Adams County, IL, Boone County, IL, Bureau County, IL, Carroll County, IL, DeKalb County, IL, Fulton County, IL, Hancock County, IL, Henderson County, IL, Henry County, IL, Knox County, IL, LaSalle County, IL, Lee County, IL, Marshall County, IL, Mason County, IL, McDonough County, IL, Mercer County, IL, Ogle County, IL, Peoria County, IL, Putnam County, IL, Rock Island County, IL, Schuyler County, IL, Stark County, IL, Stephenson County, IL, Tazewell County, IL, Warren County, IL, Whiteside County, IL, Winnebago County, IL, Woodford County, IL, Clark County, MO

The radar

The Quad Cities radar (KDVN), 68 km from the middle of the area, began a volume at 23:26 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

Lincoln, IL (KILX), launched 12:00Z, 11.4 hours before the alert went out and 169 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, Lincoln, IL at 12:00Z on 2026-04-17Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 84 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, Lincoln, IL at 12:00Z on 2026-04-17The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 65 square meters per square second.193958Sfc1 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
84 J/kg
Mixed-layer CIN
-150 J/kg
Mixed-layer LCL
1053 m above ground
0-6 km bulk shear
27 kt
0-1 km storm-relative helicity
65 m²/s²
0-3 km storm-relative helicity
164 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.1

Open this sounding in Storm Lab

The text

As transmitted.

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SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 17, 11:48 AM CDTMesoscale DiscussionSPCCarroll, Jo Daviess, Ogle, Stephenson, Winnebago2 hr
Apr 17, 12:40 PM CDTTornado WatchSPCBoone, Bureau, Carroll, DeKalb, Hancock, Henderson and 14 more9 hr
Apr 17, 2:05 PM CDTMesoscale DiscussionSPCJo Daviess55 min
Apr 17, 3:04 PM CDTMesoscale DiscussionSPCAdams, Bond, Brown, Calhoun, Cass, Christian and 20 more56 min
Apr 17, 3:31 PM CDTTornado WatchSPCAdams, Bond, Brown, Calhoun, Cass, Champaign and 50 more8 hr
Apr 17, 4:42 PM CDTMesoscale DiscussionSPCBoone, Lake, McHenry, Winnebago2 hr
Apr 17, 12:42 PM CDTMesoscale DiscussionSPCAndrew, Bates, Buchanan, Caldwell, Cass, Clay and 10 more3 hr
Apr 17, 1:40 PM CDTTornado WatchSPCAdair, Andrew, Barton, Bates, Benton, Buchanan and 40 more7 hr
Apr 17, 3:31 PM CDTMesoscale DiscussionSPCAdair, Andrew, Bates, Buchanan, Caldwell, Carroll and 23 more89 min
Apr 17, 5:10 PM CDTMesoscale DiscussionSPCAudrain, Barton, Bates, Benton, Boone, Callaway and 28 more2 hr

Nearby

Mesoscale Discussions in Illinois, 2026Mesoscale Discussions in Missouri, 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.