Alert archive / Illinois / Mesoscale Discussions in 2023

Mesoscale Discussion 577

April 20, 202327 counties in Illinois; 11 counties in Iowa; 16 counties in Wisconsin

The Storm Prediction Center issued this mesoscale discussion at Apr 20, 2023, 1:50 PM CDT for 27 counties in Illinois; 11 counties in Iowa; 16 counties in Wisconsin. It was in force for 85 min.

The area

The outline as issued.

The facts

Issued
Apr 20, 2023, 1:50 PM CDT (18:50 UTC)
Expired
Apr 20, 2023, 3:15 PM CDT
In force
85 min
Issued by
the Storm Prediction Center
Concerning
Severe potential...tornado watch likely
Chance of a watch
80%
All 54 counties

Cedar County, IA, Clinton County, IA, Delaware County, IA, Des Moines County, IA, Dubuque County, IA, Jackson County, IA, Jones County, IA, Lee County, IA, Louisa County, IA, Muscatine County, IA, Scott County, IA, Boone County, IL, Bureau County, IL, Carroll County, IL, DeKalb County, IL, DuPage County, IL, Grundy County, IL, Henderson County, IL, Henry County, IL, Jo Daviess County, IL, Kane County, IL, Kendall County, IL, Knox County, IL, LaSalle County, IL, Lee County, IL, Marshall County, IL, McHenry County, IL, Mercer County, IL, Ogle County, IL, Peoria County, IL, Putnam County, IL, Rock Island County, IL, Stark County, IL, Stephenson County, IL, Warren County, IL, Whiteside County, IL, Will County, IL, Winnebago County, IL, Columbia County, WI, Dane County, WI, Dodge County, WI, Grant County, WI, Green County, WI, Iowa County, WI, Jefferson County, WI, Kenosha County, WI, Lafayette County, WI, Milwaukee County, WI, Richland County, WI, Rock County, WI, Sauk County, WI, Walworth County, WI, Washington County, WI, Waukesha County, WI

The radar

The Quad Cities radar (KDVN), 115 km from the middle of the area, began a volume at 18:53 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

Davenport, (KDVN), launched 12:00Z, 6.8 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 2023-04-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 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 2023-04-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 44 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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
1350 m above ground
0-6 km bulk shear
60 kt
0-1 km storm-relative helicity
44 m²/s²
0-3 km storm-relative helicity
166 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

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 20, 12:25 PM CDTMesoscale DiscussionSPCAdams, Brown, Calhoun, Cass, Greene, Hancock and 6 more2 hr
Apr 20, 1:20 PM CDTSevere Thunderstorm WatchSPCAdams, Bond, Brown, Calhoun, Cass, Christian and 26 more7 hr
Apr 20, 2:06 PM CDTTornado WatchSPCBoone, Bureau, Carroll, Cook, DeKalb, DuPage and 31 more6 hr
Apr 20, 3:10 PM CDTMesoscale DiscussionSPCBond, Brown, Calhoun, Cass, Christian, Clinton and 16 more95 min
Apr 20, 3:41 PM CDTMesoscale DiscussionSPCBoone, Bureau, Carroll, DeKalb, DuPage, Fulton and 24 more94 min
Apr 20, 5:23 PM CDTMesoscale DiscussionSPCBoone, Cook, DeKalb, DuPage, Ford, Grundy and 18 more97 min
Apr 20, 5:36 PM CDTMesoscale DiscussionSPCAlexander, Bond, Calhoun, Cass, Christian, Clark and 43 more84 min
Apr 19, 8:21 PM CDTMesoscale DiscussionSPCAdair, Adams, Audubon, Boone, Calhoun, Carroll and 18 more3 hr
Apr 19, 10:58 PM CDTSevere Thunderstorm WatchSPCAdams, Benton, Black Hawk, Boone, Bremer, Buchanan and 23 more7 hr
Apr 19, 11:53 PM CDTSevere Thunderstorm WatchSPCFremont, Mills, Montgomery, Page, Pottawattamie6 hr
Apr 20, 1:28 AM CDTMesoscale DiscussionSPCFremont, Page2 hr

Nearby

Mesoscale Discussions in Illinois, 2023Mesoscale Discussions in Wisconsin, 2023Mesoscale Discussions in Iowa, 2023Every mesoscale discussion in 2023

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.