Alert archive / Illinois / Severe Thunderstorm Warnings in 2018

Severe Thunderstorm Warning 63, NWS Chicago, IL

August 31, 2018Cook County, Illinois

NWS Chicago, IL issued this severe thunderstorm warning at Aug 31, 2018, 7:40 PM CDT for Cook County, Illinois. It was in force for 20 min. No storm report in the archive falls inside the area while it was in force.

The area

The counties it named.

The facts

Issued: Aug 31, 2018, 7:40 PM CDT (00:40 UTC)
Expired: Aug 31, 2018, 8:00 PM CDT
In force: 20 min
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Hail: 0.75 in
Wind: 60.0 mph

County Cook County, IL

The radar

The Chicago radar (KLOT), 49 km from the middle of the area, began a volume at 00:43 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 00:00Z, 0.7 hours before the alert went out and 239 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1610 m above ground
0-6 km bulk shear: 8 kt
0-1 km storm-relative helicity: 138 m²/s²
0-3 km storm-relative helicity: 184 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

What forecasters said that day

The local office's own words before this severe thunderstorm warning went out, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.

NWS Chicago, IL wrote its last area forecast discussion before this severe thunderstorm warning went out at Aug 31, 6:46 PM CDT, 54 minutes earlier.

Area forecast discussion, Aug 31, 6:46 PM CDT, 54 minutes before

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Hazardous weather outlook, Aug 31, 3:15 PM CDT, 4 hours 25 minutes before

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In the hours before

Special weather statement, Aug 31, 7:23 PM CDT, 17 minutes before

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The office that day

Everything else NWS Chicago, IL issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 31, 7:23 PM CDT	Special Weather Statement	LOT	Kankakee, Will	37 min
Aug 31, 8:17 PM CDT	Special Marine Warning	LOT		88 min
Aug 31, 8:47 PM CDT	Areal Flood Advisory	LOT	Iroquois, Kankakee, Will	3 hr
Sep 1, 3:07 PM CDT	Flash Flood Watch	LOT	Boone, DeKalb, DuPage, Kane, Lake, Lee and 3 more	13 hr

Nearby

Severe Thunderstorm Warnings in Illinois, 2018 Every severe thunderstorm warning in 2018

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.