Alert archive / Illinois / Mesoscale Discussions in 2024

Mesoscale Discussion 554

April 27, 202421 counties in Illinois; 19 counties in Missouri

The Storm Prediction Center issued this mesoscale discussion at Apr 27, 2024, 9:15 PM CDT for 21 counties in Illinois; 19 counties in Missouri. It was in force for 60 min.

The area

The outline as issued.

The facts

Issued: Apr 27, 2024, 9:15 PM CDT (02:15 UTC)
Expired: Apr 27, 2024, 10:15 PM CDT
In force: 60 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...tornado watch likely
Chance of a watch: 80%

All 40 counties

Adams County, IL, Brown County, IL, Calhoun County, IL, Cass County, IL, Fulton County, IL, Greene County, IL, Jersey County, IL, Knox County, IL, Logan County, IL, Macoupin County, IL, Mason County, IL, McDonough County, IL, McLean County, IL, Menard County, IL, Morgan County, IL, Peoria County, IL, Pike County, IL, Sangamon County, IL, Schuyler County, IL, Scott County, IL, Tazewell County, IL, Audrain County, MO, Boone County, MO, Callaway County, MO, Cole County, MO, Franklin County, MO, Gasconade County, MO, Lincoln County, MO, Maries County, MO, Miller County, MO, Moniteau County, MO, Montgomery County, MO, Morgan County, MO, Osage County, MO, Phelps County, MO, Pike County, MO, Pulaski County, MO, Ralls County, MO, Saint Charles County, MO, Warren County, MO

The radar

The St Louis radar (KLSX), 63 km from the middle of the area, began a volume at 02:15 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 watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

The nearest sounding before it

Lincoln, IL (KILX), launched 00:00Z, 2.3 hours before the alert went out and 253 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-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

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: 738 J/kg
Mixed-layer CIN: -35 J/kg
Mixed-layer LCL: 786 m above ground
0-6 km bulk shear: 31 kt
0-1 km storm-relative helicity: 138 m²/s²
0-3 km storm-relative helicity: 190 m²/s²
Significant tornado parameter: 0.3
Supercell composite: 3.1

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.

Issued	Product	Office	Counties	Lasted
Apr 27, 7:58 PM CDT	Mesoscale Discussion	SPC	Boone, Bureau, DeKalb, DuPage, Fulton, Grundy and 20 more	62 min
Apr 27, 9:41 PM CDT	Tornado Watch	SPC	Adams, Brown, Calhoun, Cass, Christian, DeWitt and 23 more	6 hr
Apr 28, 1:54 AM CDT	Mesoscale Discussion	SPC	Calhoun, Greene, Jersey, Macoupin, Madison	66 min
Apr 27, 7:11 PM CDT	Mesoscale Discussion	SPC	Adair, Clark, Grundy, Knox, Putnam, Schuyler and 2 more	64 min
Apr 27, 8:25 PM CDT	Mesoscale Discussion	SPC	Barton, Bates, Benton, Carroll, Cass, Cedar and 15 more	95 min
Apr 27, 11:42 PM CDT	Tornado Watch	SPC	Barry, Barton, Benton, Cedar, Christian, Dade and 18 more	5 hr
Apr 28, 3:38 PM CDT	Mesoscale Discussion	SPC	Barry, Barton, Dade, Jasper, Lawrence, McDonald and 1 more	2 hr
Apr 28, 5:15 PM CDT	Tornado Watch	SPC	Barry, Douglas, McDonald, Newton, Ozark, Stone and 3 more	6 hr
Apr 28, 6:50 PM CDT	Mesoscale Discussion	SPC	Barry, McDonald	55 min

Nearby

Mesoscale Discussions in Illinois, 2024 Mesoscale Discussions in Missouri, 2024 Every mesoscale discussion in 2024

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.