Alert archive / Illinois / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 489
The Storm Prediction Center issued this severe thunderstorm watch at Sep 7, 2021, 1:12 PM CDT for 40 counties in Illinois; 5 counties in Indiana. It was in force for 8 hr.
The area
The outline as issued.
The facts
- Issued
- Sep 7, 2021, 1:12 PM CDT (18:12 UTC)
- Expired
- Sep 7, 2021, 9:00 PM CDT
- In force
- 8 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2 in
- Strongest gust expected
- 60 kt
All 45 counties
Boone County, IL, Bureau County, IL, Champaign County, IL, Cook County, IL, DeKalb County, IL, DeWitt County, IL, Douglas County, IL, DuPage County, IL, Edgar County, IL, Ford County, IL, Fulton County, IL, Grundy County, IL, Henderson County, IL, Henry County, IL, Iroquois County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Knox County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Logan County, IL, Marshall County, IL, Mason County, IL, McHenry County, IL, McLean County, IL, Mercer County, IL, Ogle County, IL, Peoria County, IL, Piatt County, IL, Putnam County, IL, Stark County, IL, Tazewell County, IL, Vermilion County, IL, Warren County, IL, Whiteside County, IL, Will County, IL, Woodford County, IL, Benton County, IN, Jasper County, IN, Lake County, IN, Newton County, IN, Porter County, IN
The radar
The Chicago radar (KLOT), 72 km from the middle of the area, began a volume at 18:13 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 SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 10%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 60%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 60%
- One or more hailstones of 2 inches or more
- 30%
- Six or more combined severe hail and wind reports
- 95%
Warnings issued inside it
20 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| 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 | LOT | Cook | 49 min |
| Sep 7, 2:03 PM CDT | Severe Thunderstorm Warning | LOT | Grundy, Kendall, LaSalle | 72 min |
| Sep 7, 2:15 PM CDT | Severe Thunderstorm Warning | LOT | Lake | 30 min |
| Sep 7, 2:29 PM CDT | Severe Thunderstorm Warning | LOT | Grundy, Kendall, LaSalle | 46 min |
| Sep 7, 2:57 PM CDT | Severe Thunderstorm Warning | 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 | LOT | Cook, Kankakee, Will | 62 min |
| Sep 7, 3:53 PM CDT | Severe Thunderstorm Warning | ILX | Marshall, Woodford | 37 min |
| Sep 7, 3:58 PM CDT | Severe Thunderstorm Warning | LOT | Jasper, Porter | 62 min |
| Sep 7, 4:06 PM CDT | Severe Thunderstorm Warning | LOT | Ford, Iroquois, Kankakee, LaSalle, Livingston | 54 min |
| Sep 7, 4:22 PM CDT | Severe Thunderstorm Warning | ILX | McLean, Woodford | 38 min |
| Sep 7, 4:58 PM CDT | Severe Thunderstorm Warning | ILX | McLean | 47 min |
| Sep 7, 4:58 PM CDT | Severe Thunderstorm Warning | ILX | McLean | 47 min |
| Sep 7, 4:59 PM CDT | Severe Thunderstorm Warning | LOT | Ford, Iroquois, Livingston | 61 min |
| Sep 7, 5:39 PM CDT | Severe Thunderstorm Warning | ILX | Champaign, DeWitt, McLean, Piatt | 36 min |
| Sep 7, 5:46 PM CDT | Severe Thunderstorm Warning | LOT | Grundy, Kankakee, Livingston, Will | 44 min |
| Sep 7, 6:09 PM CDT | Severe Thunderstorm Warning | ILX | Champaign, Vermilion | 51 min |
| Sep 7, 7:04 PM CDT | Severe Thunderstorm Warning | LOT | Iroquois | 56 min |
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Lincoln, IL (KILX), launched 12:00Z, 6.2 hours before the alert went out and 97 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.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 1964 m above ground
- 0-6 km bulk shear
- 25 kt
- 0-1 km storm-relative helicity
- 93 m²/s²
- 0-3 km storm-relative helicity
- 115 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
139
WWUS20 KWNS 071808
SEL9
SPC WW 071808
ILZ000-INZ000-LMZ000-080200-
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 489
NWS Storm Prediction Center Norman OK
110 PM CDT Tue Sep 7 2021
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Northern Illinois
Northwest Indiana
Lake Michigan
* Effective this Tuesday afternoon and evening from 110 PM until
900 PM CDT.
* Primary threats include...
Scattered large hail likely with isolated very large hail events
to 2 inches in diameter possible
Scattered damaging wind gusts to 70 mph likely
SUMMARY...A line of thunderstorms currently developing from northern
Illinois into eastern Iowa will spread across the watch area this
afternoon and early evening. Damaging winds and hail will be
possible with the strongest cells.
The severe thunderstorm watch area is approximately along and 60
statute miles north and south of a line from 85 miles east of
Marseilles IL to 45 miles west northwest of Peoria IL. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU9).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.
&&
OTHER WATCH INFORMATION...CONTINUE...WW 488...
AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
26035.
...HartSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 7, 12:25 PM CDT | Mesoscale Discussion | SPC | Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 9 more | 65 min |
| Sep 7, 3:14 PM CDT | Mesoscale Discussion | SPC | DuPage, Ford, Grundy, Iroquois, Kankakee, Kendall and 11 more | 91 min |
| Sep 7, 5:25 PM CDT | Mesoscale Discussion | SPC | Champaign, Vermilion | 95 min |
| Sep 7, 1:48 PM CDT | Mesoscale Discussion | SPC | DeKalb, Elkhart, Fulton, Kosciusko, LaGrange, LaPorte and 6 more | 117 min |
| Sep 7, 2:20 PM CDT | Severe Thunderstorm Watch | SPC | Cass, Elkhart, Fulton, Kosciusko, LaGrange, LaPorte and 7 more | 7 hr |
| Sep 7, 4:37 PM CDT | Mesoscale Discussion | SPC | Elkhart, Fulton, Kosciusko, LaGrange, LaPorte, Marshall and 5 more | 83 min |
Nearby
Severe Thunderstorm Watches in Illinois, 2021Severe Thunderstorm Watches in Indiana, 2021Every severe thunderstorm watch 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; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.