Alert archive / Illinois / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 462
The Storm Prediction Center issued this severe thunderstorm watch at Aug 24, 2021, 3:55 PM CDT for 10 counties in Illinois; 4 counties in Wisconsin. It was in force for 5 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 24, 2021, 3:55 PM CDT (20:55 UTC)
- Expired
- Aug 24, 2021, 8:32 PM CDT
- In force
- 5 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
Counties Boone County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Kane County, IL, Lake County, IL, Lee County, IL, McHenry County, IL, Ogle County, IL, Winnebago County, IL, Green County, WI, Lafayette County, WI, Rock County, WI, Walworth County, WI
The radar
The Milwaukee radar (KMKX), 81 km from the middle of the area, began a volume at 20:56 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
- 5%
- Ten or more severe wind reports
- 40%
- One or more gusts of 65 knots or more
- 10%
- Ten or more severe hail reports
- 40%
- One or more hailstones of 2 inches or more
- 20%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
9 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 24, 4:13 PM CDT | Severe Thunderstorm Warning | MKX | Lafayette | 32 min |
| Aug 24, 4:18 PM CDT | Severe Thunderstorm Warning | MKX | Iowa, Lafayette | 27 min |
| Aug 24, 4:39 PM CDT | Severe Thunderstorm Warning | MKX | Lafayette | 47 min |
| Aug 24, 5:26 PM CDT | Severe Thunderstorm Warning | LOT | Boone, Lee, Ogle, Winnebago | 64 min |
| Aug 24, 5:40 PM CDT | Flash Flood Warning | LOT | Boone, McHenry | 4 hr |
| Aug 24, 6:09 PM CDT | Severe Thunderstorm Warning | LOT | Boone, DeKalb, Kane, Lee, McHenry, Ogle | 66 min |
| Aug 24, 6:10 PM CDT | Severe Thunderstorm Warning | MKX | Rock | 33 min |
| Aug 24, 6:36 PM CDT | Flash Flood Warning | LOT | Cook, DuPage, Lake | 3 hr |
| Aug 24, 7:08 PM CDT | Severe Thunderstorm Warning | LOT | Cook, DuPage, Kane, Lake, McHenry | 67 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
Davenport, (KDVN), launched 12:00Z, 8.9 hours before the alert went out and 145 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
- 1809 J/kg
- Mixed-layer CIN
- -127 J/kg
- Mixed-layer LCL
- 1284 m above ground
- 0-6 km bulk shear
- 15 kt
- 0-1 km storm-relative helicity
- 35 m²/s²
- 0-3 km storm-relative helicity
- 9 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
025 WWUS20 KWNS 242052 SEL2 SPC WW 242052 ILZ000-WIZ000-250400- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 462 NWS Storm Prediction Center Norman OK 350 PM CDT Tue Aug 24 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of northern Illinois southern Wisconsin * Effective this Tuesday afternoon and evening from 350 PM until 1100 PM CDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Scattered large hail events to 1.5 inches in diameter possible SUMMARY...An organized cluster of thunderstorms may continue developing eastward out of northeastern Iowa into far southern Wisconsin and northern Illinois, posing a risk for damaging wind gusts before weakening this evening. The severe thunderstorm watch area is approximately along and 45 statute miles north and south of a line from 40 miles west of Rockford IL to 70 miles east of Rockford IL. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU2). 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 461... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 27035. ...Kerr
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 24, 6:00 AM CDT | Mesoscale Discussion | SPC | Jo Daviess | 90 min |
| Aug 24, 1:52 PM CDT | Severe Thunderstorm Watch | SPC | Carroll, Jo Daviess, Rock Island, Stephenson, Whiteside | 5 hr |
| Aug 24, 3:09 PM CDT | Mesoscale Discussion | SPC | Boone, McHenry, Ogle, Stephenson, Winnebago | 66 min |
| Aug 24, 5:10 PM CDT | Mesoscale Discussion | SPC | Boone, Carroll, DeKalb, DuPage, Jo Daviess, Kane and 7 more | 2 hr |
| Aug 24, 2:17 AM CDT | Severe Thunderstorm Watch | SPC | Pierce, Polk, Saint Croix | 7 hr |
| Aug 24, 3:00 AM CDT | Mesoscale Discussion | SPC | Pierce, Polk, Saint Croix | 2 hr |
| Aug 24, 7:10 AM CDT | Mesoscale Discussion | SPC | Adams, Barron, Buffalo, Chippewa, Clark, Dunn and 15 more | 95 min |
| Aug 24, 9:13 AM CDT | Mesoscale Discussion | SPC | Brown, Calumet, Menominee, Oconto, Outagamie, Shawano and 3 more | 62 min |
| Aug 24, 12:44 PM CDT | Mesoscale Discussion | SPC | Crawford, Grant, Iowa, Richland, Sauk, Vernon | 91 min |
Nearby
Severe Thunderstorm Watches in Illinois, 2021Severe Thunderstorm Watches in Wisconsin, 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.