Alert archive / Illinois / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 72, NWS Chicago, IL

August 11, 2021Grundy County, Kane County, Kendall County, Illinois

NWS Chicago, IL issued this severe thunderstorm warning at Aug 11, 2021, 9:05 AM CDT for Grundy County, Kane County, Kendall County, Illinois. It was in force for 40 min. 15 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Aug 11, 2021, 9:05 AM CDT (14:05 UTC)
Expired: Aug 11, 2021, 9:45 AM CDT
In force: 40 min
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Damage threat: Considerable
Hail: 0.75 in
Wind: 70.0 mph

Counties Grundy County, IL, Kane County, IL, Kendall County, IL

The radar

The Chicago radar (KLOT), 26 km from the middle of the area, began a volume at 14:04 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.

What was reported inside it

Time	Report	Where	Remark
Aug 11, 9:18 AM CDT	TSTM WND DMG	1 W Plano, IL	TREE DOWNED ON LITTLE ROCK RD WEST OF PLANO.
Aug 11, 9:18 AM CDT	TSTM WND DMG	2 Sw Plano, IL	SEVERAL TREES SNAPPED OR DOWNED BETWEEN SANDWICH AND PLANO.
Aug 11, 9:22 AM CDT	TSTM WND DMG	3 Ssw Big Rock, IL	LARGE OAK TREE SNAPPED AT BASE.
Aug 11, 9:24 AM CDT	TSTM WND GST 68	Plano, IL	PRIVATE WEATHER STATION REPORTED PEAK WIND GUST OF 68 MPH. WINDS GUSTED ABOVE 60 MPH FOR 15 MINUTES.
Aug 11, 9:28 AM CDT	TSTM WND DMG	2 N Sugar Grove, IL	LARGE TREE SNAPPED.
Aug 11, 9:28 AM CDT	TSTM WND DMG	Oswego, IL	LARGE TREE LIMB DOWNED AND FENCE BLOWN OVER.
Aug 11, 9:28 AM CDT	TSTM WND GST 64	2 Wnw Sugar Grove, IL	KARR ASOS PEAK GUST.
Aug 11, 9:29 AM CDT	TSTM WND DMG	Oswego, IL	HALF OF TREE SNAPPED AT ITS FORK.
Aug 11, 9:30 AM CDT	TSTM WND DMG	Boulder Hill, IL	MULTIPLE LARGE TREE LIMBS DOWNED IN BOULDER HILL.
Aug 11, 9:33 AM CDT	TSTM WND DMG	Aurora, IL	LARGE TREE LIMB DOWNED IN WILDER PARK IN AURORA AND NEARBY POWER POLE TILTED.
Aug 11, 9:34 AM CDT	TSTM WND DMG	North Aurora, IL	LARGE TREE SNAPPED.
Aug 11, 9:35 AM CDT	TSTM WND DMG	2 W Aurora, IL	12 INCH DIAMETER LIMB DOWNED.
Aug 11, 9:35 AM CDT	TSTM WND GST 55	5 Se Lisbon, IL	AWOS STATION KC09 MORRIS AIRPORT.
Aug 11, 9:35 AM CDT	TSTM WND GST 68	3 Wsw Montgomery, IL	PEAK GUST ON PERSONAL WEATHER STATION.
Aug 11, 9:37 AM CDT	TSTM WND DMG	Minooka, IL	LARGE TREE DOWNED.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The watch it was issued in

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

Issued	Product	Office	Lasted
Aug 11, 8:52 AM CDT	Severe Thunderstorm Watch	SPC	4 hr

The nearest sounding before it

Lincoln, IL (KILX), launched 12:00Z, 2.1 hours before the alert went out and 164 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: 1930 J/kg
Mixed-layer CIN: -174 J/kg
Mixed-layer LCL: 1253 m above ground
0-6 km bulk shear: 28 kt
0-1 km storm-relative helicity: 228 m²/s²
0-3 km storm-relative helicity: 185 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 4.4

Open this sounding in Storm Lab

The text

As transmitted.

813 
WUUS53 KLOT 111405
SVRLOT
ILC063-089-093-111445-
/O.NEW.KLOT.SV.W.0072.210811T1405Z-210811T1445Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Chicago/Romeoville
905 AM CDT Wed Aug 11 2021

The National Weather Service in Chicago has issued a

* Severe Thunderstorm Warning for...
  Kendall County in northeastern Illinois...
  Northern Grundy County in northeastern Illinois...
  Southern Kane County in northeastern Illinois...

* Until 945 AM CDT.

* At 905 AM CDT, a severe thunderstorm was located near Earlville, or
  8 miles west of Sheridan, moving east at 65 mph.

  HAZARD...70 mph wind gusts. The strongest winds will move into 
           Kendall county! 

  SOURCE...Radar indicated.

  IMPACT...Expect considerable tree damage. Damage is likely to 
           mobile homes, roofs, and outbuildings.

* Locations impacted include...
  Aurora, Joliet, Plainfield, Oswego, Batavia, Yorkville, Morris,
  Channahon, Minooka, Plano, Sandwich, Coal City, Montgomery, North
  Aurora, Sugar Grove, Boulder Hill, Diamond, Newark, Millington and
  Big Rock.

Including the following interstates...
 I-80 between mile markers 104 and 122.
 I-88 between mile markers 108 and 120.

This includes...  Aurora University, Gebhard Woods State Park, Grundy
County Speedway and Fairgrounds, IL Math and Science Academy,
Waubonsee Community College, and William G Stratton State Park.
 
PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4184 8826 4127 8825 4127 8859 4184 8860
TIME...MOT...LOC 1405Z 264DEG 58KT 4155 8884 

THUNDERSTORM DAMAGE THREAT...CONSIDERABLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...70 MPH

$$

Borchardt

2 follow-up statements

578 
WWUS53 KLOT 111422
SVSLOT

Severe Weather Statement
National Weather Service Chicago/Romeoville
922 AM CDT Wed Aug 11 2021

ILC063-089-093-111445-
/O.CON.KLOT.SV.W.0072.000000T0000Z-210811T1445Z/
Kendall IL-Grundy IL-Kane IL-
922 AM CDT Wed Aug 11 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 945 AM CDT
FOR KENDALL...NORTHERN GRUNDY AND SOUTHERN KANE COUNTIES...

At 922 AM CDT, a severe thunderstorm was located near Yorkville,
moving east at 65 mph.

HAZARD...70 mph wind gusts. The damaging winds may last longer than 
         30 minutes! 

SOURCE...Radar indicated.

IMPACT...Expect considerable tree damage. Damage is likely to mobile 
         homes, roofs, and outbuildings.

Locations impacted include...
Aurora, Joliet, Plainfield, Oswego, Batavia, Yorkville, Morris,
Channahon, Minooka, Plano, Sandwich, Coal City, Montgomery, North
Aurora, Sugar Grove, Boulder Hill, Diamond, Newark, Millington and
Big Rock.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4184 8826 4127 8825 4127 8859 4184 8860
TIME...MOT...LOC 1422Z 264DEG 58KT 4158 8847 

THUNDERSTORM DAMAGE THREAT...CONSIDERABLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...70 MPH

$$

Borchardt

714 
WWUS53 KLOT 111438
SVSLOT

Severe Weather Statement
National Weather Service Chicago/Romeoville
938 AM CDT Wed Aug 11 2021

ILC063-089-093-111445-
/O.CON.KLOT.SV.W.0072.000000T0000Z-210811T1445Z/
Kendall IL-Grundy IL-Kane IL-
938 AM CDT Wed Aug 11 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 945 AM CDT
FOR KENDALL...NORTHERN GRUNDY AND SOUTHERN KANE COUNTIES...

At 937 AM CDT, a severe thunderstorm was located near Crest Hill, or
near Plainfield, moving east at 65 mph.

HAZARD...70 mph wind gusts. This storm is producing widespread wind 
         damage! 

SOURCE...Trained Spotters. 

IMPACT...Expect considerable tree damage. Damage is likely to mobile 
         homes, roofs, and outbuildings.

Locations impacted include...
Aurora, Joliet, Plainfield, Oswego, Batavia, Yorkville, Morris,
Channahon, Minooka, Plano, Sandwich, Coal City, Montgomery, North
Aurora, Sugar Grove, Boulder Hill, Diamond, Newark, Millington and
Big Rock.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

For your protection move to an interior room on the lowest floor of a
building.

&&

LAT...LON 4184 8826 4127 8825 4127 8859 4184 8860
TIME...MOT...LOC 1437Z 264DEG 58KT 4161 8813 

THUNDERSTORM DAMAGE THREAT...CONSIDERABLE
HAIL THREAT...RADAR INDICATED
MAX HAIL SIZE...<.75 IN
WIND THREAT...OBSERVED
MAX WIND GUST...70 MPH

$$

Borchardt

The office that day

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

Issued	Product	Office	Counties	Lasted
Aug 10, 7:03 PM CDT	Special Marine Warning	LOT		117 min
Aug 10, 7:11 PM CDT	Severe Thunderstorm Warning	LOT	Will	49 min
Aug 10, 7:13 PM CDT	Severe Thunderstorm Warning	LOT	DeKalb, LaSalle	47 min
Aug 10, 9:22 PM CDT	Special Weather Statement	LOT	Kankakee	53 min
Aug 11, 6:39 AM CDT	Small Craft Advisory	LOT		15 hr
Aug 11, 8:25 AM CDT	Severe Thunderstorm Warning	LOT	Lee	50 min
Aug 11, 8:41 AM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	DeKalb, LaSalle, Lee	49 min
Aug 11, 9:25 AM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	DuPage, Kane, Will	65 min
Aug 11, 9:35 AM CDT	Severe Thunderstorm Warning	LOT	Boone, DeKalb, Ogle, Winnebago	42 min
Aug 11, 9:40 AM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	Cook, Will	65 min
Aug 11, 9:46 AM CDT	Severe Thunderstorm Warning	LOT	Kane, Lake, McHenry	59 min
Aug 11, 9:47 AM CDT	Special Marine Warning	LOT		118 min
Aug 11, 9:50 AM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	Grundy, Kane, Kendall	40 min
Aug 11, 10:24 AM CDT	Special Weather Statement	LOT	Iroquois, Kankakee	66 min
Aug 11, 12:06 PM CDT	Special Marine Warning	LOT		54 min

Nearby

Severe Thunderstorm Warnings in Illinois, 2021 Every severe thunderstorm warning in 2021

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.