Alert archive / Illinois / Severe Thunderstorm Warnings in 2018

Severe Thunderstorm Warning 69, NWS Chicago, IL

September 25, 20187 counties in Illinois

NWS Chicago, IL issued this severe thunderstorm warning at Sep 25, 2018, 4:52 PM CDT for 7 counties in Illinois. It was in force for 68 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: Sep 25, 2018, 4:52 PM CDT (21:52 UTC)
Expired: Sep 25, 2018, 6:00 PM CDT
In force: 68 min
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Tornado: Possible
Hail: 0.75 in
Wind: 70.0 mph

Counties Cook County, IL, DuPage County, IL, Kane County, IL, Kendall County, IL, Lake County, IL, McHenry County, IL, Will County, IL

The radar

The Chicago radar (KLOT), 35 km from the middle of the area, began a volume at 21:52 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 watch it was issued in

The SPC watch in force over the same counties when this warning went out.

Issued	Product	Office	Lasted
Sep 25, 1:36 PM CDT	Severe Thunderstorm Watch	SPC	8 hr

The nearest sounding before it

Davenport, (KDVN), launched 12:00Z, 9.9 hours before the alert went out and 200 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: 47 J/kg
Mixed-layer CIN: -108 J/kg
Mixed-layer LCL: 703 m above ground
0-6 km bulk shear: 41 kt
0-1 km storm-relative helicity: 4 m²/s²
0-3 km storm-relative helicity: 38 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 Sep 25, 4:16 PM CDT, 36 minutes earlier.

Area forecast discussion, Sep 25, 4:16 PM CDT, 36 minutes before

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Hazardous weather outlook, Sep 25, 3:20 PM CDT, 1 hour 32 minutes before

Hazardous Weather Outlook
National Weather Service Chicago/Romeoville IL
320 PM CDT Tue Sep 25 2018

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
262030-
Winnebago-Boone-McHenry-Lake IL-Ogle-Lee-DeKalb-Kane-DuPage-Cook-
La Salle-Kendall-Grundy-Will-Kankakee-Livingston-Iroquois-Ford-
Lake IN-Porter-Newton-Jasper-Benton-
320 PM CDT Tue Sep 25 2018 /420 PM EDT Tue Sep 25 2018/

This Hazardous Weather Outlook is for portions of North Central
Illinois...Northeast Illinois and Northwest Indiana.

.DAY ONE...Tonight.

Weather hazards expected...

  Significant Thunderstorm Risk...with an associated:
     Limited Tornado risk.
     Elevated damaging wind risk...up to 60 mph.
     Limited hail risk...up to Nickel size.
  Limited Flooding Risk.

DISCUSSION...

Scattered thunderstorms are likely to move across the area this
evening. The greatest chance of thunderstorms, including some
potential for isolated severe thunderstorms is through 10 pm this
evening. The primary severe threat is isolated damaging wind gusts
up to 60 mph. An isolated tornado or two also cannot be ruled
out.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Sunday and Monday...
  Limited Thunderstorm Risk.

.SPOTTER INFORMATION STATEMENT...

  Spotters will likely be needed through this evening.

GENERAL STORM MOTION OF THE DAY:

  Moving toward the east northeast at 45 mph.

LMZ740>745-262030-
Winthrop Harbor to Wilmette Harbor-
Wilmette Harbor to Northerly Island-
Northerly Island to Calumet Harbor-Calumet Harbor to Gary-
Gary to Burns Harbor-Burns Harbor to Michigan City-
320 PM CDT Tue Sep 25 2018

This Hazardous Weather Outlook is for portions of the Illinois
nearshore waters of Lake Michigan and the Indiana nearshore
waters of Lake Michigan.

.DAY ONE...Tonight.

Weather hazards expected...

  Hazardous conditions for small craft.
  Significant Thunderstorm Risk...with an associated:
     Limited Waterspout Risk.
     Elevated thunderstorm wind gust risk...up to 50 knots.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Wednesday...
  Hazardous conditions for small craft are likely.
Sunday and Monday...
  Limited Thunderstorm Risk.

KJB

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In the hours before

Local storm report, Sep 25, 4:16 PM CDT, 36 minutes before

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Local storm report, Sep 25, 4:23 PM CDT, 29 minutes before

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Local storm report, Sep 25, 4:25 PM CDT, 27 minutes before

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Local storm report, Sep 25, 4:34 PM CDT, 18 minutes before

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Local storm report, Sep 25, 4:48 PM CDT, 4 minutes before

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Special weather statement, Sep 25, 4:52 PM CDT, 0 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
Sep 25, 3:15 AM CDT	Small Craft Advisory	LOT		37 hr
Sep 25, 3:27 PM CDT	Severe Thunderstorm Warning	LOT	Lee, Ogle, Winnebago	48 min
Sep 25, 4:01 PM CDT	Severe Thunderstorm Warning	LOT	Boone, DeKalb, Kane, Kendall, LaSalle, Lee and 2 more	59 min
Sep 25, 4:34 PM CDT	Special Marine Warning	LOT		116 min
Sep 25, 4:52 PM CDT	Special Weather Statement	LOT	LaSalle	38 min
Sep 25, 5:35 PM CDT	Special Weather Statement	LOT	Grundy, Will	55 min
Sep 25, 5:59 PM CDT	Special Weather Statement	LOT	Kankakee, Will	61 min
Sep 25, 6:25 PM CDT	Special Marine Warning	LOT		50 min
Sep 25, 6:29 PM CDT	Severe Thunderstorm Warning	LOT	Cook	31 min
Sep 25, 6:54 PM CDT	Special Weather Statement	LOT	Iroquois	66 min
Sep 25, 2:49 PM CDT	Beach Hazards Statement	LOT	Porter	25 hr
Sep 25, 6:47 PM CDT	Severe Thunderstorm Warning	LOT	Porter	28 min

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.