Alert archive / Illinois / Severe Thunderstorm Warnings in 2021

Severe Thunderstorm Warning 99, NWS Chicago, IL

September 7, 2021Grundy County, Kendall County, LaSalle County, Illinois

NWS Chicago, IL issued this severe thunderstorm warning at Sep 7, 2021, 2:03 PM CDT for Grundy County, Kendall County, LaSalle County, Illinois. It was in force for 72 min. 14 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: Sep 7, 2021, 2:03 PM CDT (19:03 UTC)
Expired: Sep 7, 2021, 3:15 PM CDT
In force: 72 min
Issued by: NWS Chicago, IL
Area: Storm-based polygon
Damage threat: Considerable
Hail: 1.75 in
Wind: 60.0 mph

Counties Grundy County, IL, Kendall County, IL, LaSalle County, IL

The radar

The Chicago radar (KLOT), 50 km from the middle of the area, began a volume at 19:06 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
Sep 7, 2:18 PM CDT	HAIL 1.75	4 Wnw Earlville, IL	TIME ESTIMATED FROM RADAR.
Sep 7, 2:25 PM CDT	HAIL 2	Earlville, IL	MULTIPLE REPORTS OF HAIL UP TO 2 INCHES IN DIAMETER IN AND NEAR EARLVILLE. TIME ESTIMATED FROM RADAR.
Sep 7, 2:52 PM CDT	TSTM WND DMG	4 Ssw Leland, IL	REPORT VIA NWS CHAT FROM SPOTTER OF 3 INCH DIAMETER TREE BRANCH DOWN NEAR LELAND, IL.
Sep 7, 2:54 PM CDT	TSTM WND DMG	6 Ne Seneca, IL	NUMEROUS TREES DOWNED AND ONE SNAPPED IN HALF ALONG US ROUTE 6 BETWEEN MORRIS AND SENECA. POWER POLE ALSO DAMAGED. TIME ESTIMATED FROM RADAR.
Sep 7, 2:55 PM CDT	TSTM WND DMG	Morris, IL	NUMEROUS TREES AND WIRES DOWNED IN AND AROUND MORRIS. TIME ESTIMATED FROM RADAR.
Sep 7, 2:55 PM CDT	TSTM WND DMG	Morris, IL	REPORT OF 16 INCH DIAMETER TREE SNAPPED. TIME ESTIMATED BY RADAR. LOCATION IS APPROXIMATE.
Sep 7, 2:55 PM CDT	TSTM WND GST 61	5 Se Lisbon, IL	WIND GUST OF 61 MPH (53 KTS) REPORTED BY C09 ASOS.
Sep 7, 2:55 PM CDT	TSTM WND GST 72	3 E Lisbon, IL
Sep 7, 2:59 PM CDT	TSTM WND DMG	3 Wsw Plattville, IL	REPORT OF TREE BRANCHES AND LIMBS DOWNED BY WINDS ESTIMATED TO BE 60 TO 65 MPH.
Sep 7, 3:01 PM CDT	TORNADO	2 Nnw Minooka, IL	TWO SPOTTERS REPORTED THAT A BRIEF TORNADO TOUCHED DOWN NORTH OF MINOOKA. TIME ESTIMATED FROM RADAR.
Sep 7, 3:02 PM CDT	TSTM WND DMG	Minooka, IL	PICTURES OF TREE BRANCHES DOWNED ON A HOUSE VIA SOCIAL MEDIA. TIME ESTIMATED BY RADAR.
Sep 7, 3:02 PM CDT	TSTM WND GST 85	Minooka, IL	AN NWS STORM DAMAGE SURVEY TEAM FOUND WIDESPREAD TREE DAMAGE, INCLUDING NUMEROUS DOWNED, ACROSS MUCH OF AND NEAR MINOOKA. SOME OF THESE TREES WERE DOWNED ON STRUCTURES. THE DAMAGE WAS CONSISTENT WITH THE HIGHEST WIND GUSTS TO AROUND 85 MPH.
Sep 7, 3:07 PM CDT	TSTM WND DMG	1 Wsw Minooka, IL	REPORT VIA SOCIAL MEDIA OF TRACTOR TRAILERS OVERTURNED AT A COLD STORAGE FACILITY. TIME IS ESTIMATED FROM RADAR.
Sep 7, 3:15 PM CDT	TSTM WND DMG	Minooka, IL	SPOTTER REPORTS TREE BRANCHES DOWN. WINDS WERE ESTIMATED TO BE 60 MPH.

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
Sep 7, 1:12 PM CDT	Severe Thunderstorm Watch	SPC	8 hr

The nearest sounding before it

Davenport, (KDVN), launched 12:00Z, 7.1 hours before the alert went out and 151 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: 827 J/kg
Mixed-layer CIN: -263 J/kg
Mixed-layer LCL: 1475 m above ground
0-6 km bulk shear: 39 kt
0-1 km storm-relative helicity: 185 m²/s²
0-3 km storm-relative helicity: 167 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

As transmitted.

532 
WUUS53 KLOT 071903
SVRLOT
ILC063-093-099-072015-
/O.NEW.KLOT.SV.W.0099.210907T1903Z-210907T2015Z/

BULLETIN - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Warning
National Weather Service Chicago/Romeoville
203 PM CDT Tue Sep 7 2021

The National Weather Service in Chicago has issued a

* Severe Thunderstorm Warning for...
  Kendall County in northeastern Illinois...
  Northern La Salle County in north central Illinois...
  Northern Grundy County in northeastern Illinois...

* Until 315 PM CDT.

* At 203 PM CDT, severe thunderstorms were located along a line
  extending from near Shabbona to near Sublette, moving southeast at
  35 mph.

  HAZARD...Golf ball size hail and 60 mph wind gusts.

  SOURCE...Trained weather spotters.

  IMPACT...People and animals outdoors will be injured. Expect hail 
           damage to roofs, siding, windows, and vehicles. Expect 
           wind damage to roofs, siding, and trees.

* Locations impacted include...
  Aurora, Joliet, Plainfield, Oswego, Ottawa, Yorkville, Morris,
  Channahon, Minooka, Plano, Sandwich, Mendota, Sheridan, Montgomery,
  Boulder Hill, Lake Holiday, Somonauk, Earlville, Serena and Newark.

Including the following interstates...
 I-39 between mile markers 67 and 77.
 I-80 between mile markers 91 and 122.

This includes...  Gebhard Woods State Park, Grundy County Speedway
and Fairgrounds, Tri-County Fairgrounds, 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 4163 8860 4172 8860 4172 8826 4133 8825
      4135 8879 4154 8917 4163 8917
TIME...MOT...LOC 1903Z 293DEG 29KT 4178 8883 4161 8919 

THUNDERSTORM DAMAGE THREAT...CONSIDERABLE
HAIL THREAT...OBSERVED
MAX HAIL SIZE...1.75 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...60 MPH

$$

Petr

3 follow-up statements

603 
WWUS53 KLOT 071920
SVSLOT

Severe Weather Statement
National Weather Service Chicago/Romeoville
220 PM CDT Tue Sep 7 2021

ILC063-093-099-072015-
/O.CON.KLOT.SV.W.0099.000000T0000Z-210907T2015Z/
Kendall IL-La Salle IL-Grundy IL-
220 PM CDT Tue Sep 7 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 315 PM CDT
FOR KENDALL...NORTHERN LA SALLE AND NORTHERN GRUNDY COUNTIES...

At 218 PM CDT, severe thunderstorms were located along a line 
extending from near Leland to near Mendota, moving southeast at 35 
mph.

HAZARD...Two inch hail and 70 mph wind gusts.

SOURCE...Trained weather spotters reported golf ball sized hail near 
         Compton.

IMPACT...People and animals outdoors will be injured. Expect hail 
         damage to roofs, siding, windows, and vehicles. Expect 
         considerable tree damage. Wind damage is also likely to 
         mobile homes, roofs, and outbuildings.

Locations impacted include...
Aurora, Joliet, Plainfield, Oswego, Ottawa, Yorkville, Morris,
Channahon, Minooka, Plano, Sandwich, Mendota, Sheridan, Montgomery,
Boulder Hill, Lake Holiday, Somonauk, Earlville, Serena and Newark.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 4163 8860 4172 8860 4172 8826 4133 8825
      4135 8879 4154 8917 4163 8917
TIME...MOT...LOC 1918Z 292DEG 31KT 4167 8876 4158 8902 

THUNDERSTORM DAMAGE THREAT...CONSIDERABLE
HAIL THREAT...OBSERVED
MAX HAIL SIZE...2.00 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...70 MPH

$$

Petr

568 
WWUS53 KLOT 071938
SVSLOT

Severe Weather Statement
National Weather Service Chicago/Romeoville
238 PM CDT Tue Sep 7 2021

ILC063-093-099-072015-
/O.CON.KLOT.SV.W.0099.000000T0000Z-210907T2015Z/
Kendall IL-La Salle IL-Grundy IL-
238 PM CDT Tue Sep 7 2021

...A SEVERE THUNDERSTORM WARNING REMAINS IN EFFECT UNTIL 315 PM CDT
FOR KENDALL...NORTHERN LA SALLE AND NORTHERN GRUNDY COUNTIES...

At 236 PM CDT, severe thunderstorms were located along a line 
extending from near Sandwich to near Mendota, moving southeast at 35 
mph. The most intense part of this storm is located southeast of 
Earlville.

HAZARD...Tennis ball size hail and 70 mph wind gusts.

SOURCE...Trained weather spotters reported golf ball sized hail near 
         Compton.

IMPACT...People and animals outdoors will be injured. Expect hail 
         damage to roofs, siding, windows, and vehicles. Expect 
         considerable tree damage. Wind damage is also likely to 
         mobile homes, roofs, and outbuildings.

Locations impacted include...
Aurora, Joliet, Plainfield, Oswego, Ottawa, Yorkville, Morris,
Channahon, Minooka, Plano, Sandwich, Mendota, Sheridan, Montgomery,
Boulder Hill, Lake Holiday, Somonauk, Earlville, Serena and Newark.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

These storms are producing large hail. SEEK SHELTER NOW inside a
sturdy structure and stay away from windows.

&&

LAT...LON 4163 8860 4172 8860 4172 8826 4133 8825
      4135 8879 4154 8917 4159 8917 4163 8899
TIME...MOT...LOC 1936Z 293DEG 29KT 4161 8858 4152 8884 

THUNDERSTORM DAMAGE THREAT...CONSIDERABLE
HAIL THREAT...OBSERVED
MAX HAIL SIZE...2.50 IN
WIND THREAT...RADAR INDICATED
MAX WIND GUST...70 MPH

$$

Petr

632 
WWUS53 KLOT 072016
SVSLOT

Severe Weather Statement
National Weather Service Chicago/Romeoville
316 PM CDT Tue Sep 7 2021

ILC063-093-099-072026-
/O.EXP.KLOT.SV.W.0099.000000T0000Z-210907T2015Z/
Kendall IL-La Salle IL-Grundy IL-
316 PM CDT Tue Sep 7 2021

...THE SEVERE THUNDERSTORM WARNING FOR KENDALL...NORTHERN LA SALLE
AND NORTHERN GRUNDY COUNTIES HAS EXPIRED...
    
The storms which prompted the warning is moving out of the area.
Therefore, the warning has been allowed to expire. However, severe 
thunderstorm warnings continue for northern Grundy and southeastern 
Kendall. 

A Severe Thunderstorm Watch remains in effect until 900 PM CDT for
north central and northeastern Illinois.

LAT...LON 4163 8860 4172 8860 4172 8826 4133 8825
      4135 8879 4154 8917 4159 8917 4163 8899
TIME...MOT...LOC 2016Z 293DEG 29KT 4149 8820 4140 8846 

$$

Birk

The office that day

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

Issued	Product	Office	Counties	Lasted
Sep 6, 9:29 PM CDT	Small Craft Advisory	LOT		55 hr
Sep 7, 12:37 PM CDT	Severe Thunderstorm Warning	LOT	Boone, McHenry, Winnebago	53 min
Sep 7, 12:47 PM CDT	Special Marine Warning	LOT		118 min
Sep 7, 1:13 PM CDT	Special Weather Statement	LOT	Boone, DeKalb, Kane, Lee, Ogle	32 min
Sep 7, 1:20 PM CDT	Severe Thunderstorm Warning	LOT	Lake, McHenry	55 min
Sep 7, 1:23 PM CDT	Severe Thunderstorm Warning	LOT	DeKalb, Kane, Lee, Ogle	67 min
Sep 7, 1:41 PM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	Cook	49 min
Sep 7, 1:51 PM CDT	Special Marine Warning	LOT		3 hr
Sep 7, 2:15 PM CDT	Areal Flood Advisory	LOT	Lake, McHenry	3 hr
Sep 7, 2:15 PM CDT	Severe Thunderstorm Warning	LOT	Lake	30 min
Sep 7, 2:29 PM CDT	Severe Thunderstorm Warning Destructive damage threat	LOT	Grundy, Kendall, LaSalle	46 min
Sep 7, 2:41 PM CDT	Special Marine Warning	LOT		94 min
Sep 7, 2:57 PM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	Grundy, Kankakee, Kendall, LaSalle, Will	63 min
Sep 7, 3:04 PM CDT	Tornado Warning	LOT	Will	26 min
Sep 7, 3:28 PM CDT	Severe Thunderstorm Warning Considerable damage threat	LOT	Cook, Kankakee, Will	62 min
Sep 7, 4:06 PM CDT	Severe Thunderstorm Warning	LOT	Ford, Iroquois, Kankakee, LaSalle, Livingston	54 min
Sep 7, 4:34 PM CDT	Special Weather Statement	LOT	Kankakee	56 min
Sep 7, 4:59 PM CDT	Severe Thunderstorm Warning	LOT	Ford, Iroquois, Livingston	61 min
Sep 7, 5:21 PM CDT	Special Weather Statement	LOT	Grundy	39 min
Sep 7, 5:46 PM CDT	Severe Thunderstorm Warning	LOT	Grundy, Kankakee, Livingston, Will	44 min
Sep 7, 6:53 PM CDT	Areal Flood Advisory	LOT	Iroquois, Kankakee	3 hr

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.