Alert archive / Iowa / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 461
The Storm Prediction Center issued this severe thunderstorm watch at Aug 24, 2021, 1:52 PM CDT for 5 counties in Illinois; 42 counties in Iowa; Grant County, Wisconsin. It was in force for 5 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 24, 2021, 1:52 PM CDT (18:52 UTC)
- Expired
- Aug 24, 2021, 7:00 PM CDT
- In force
- 5 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 48 counties
Audubon County, IA, Benton County, IA, Black Hawk County, IA, Boone County, IA, Bremer County, IA, Buchanan County, IA, Butler County, IA, Calhoun County, IA, Carroll County, IA, Cedar County, IA, Chickasaw County, IA, Clayton County, IA, Clinton County, IA, Crawford County, IA, Dallas County, IA, Delaware County, IA, Dubuque County, IA, Fayette County, IA, Franklin County, IA, Greene County, IA, Grundy County, IA, Guthrie County, IA, Hamilton County, IA, Hardin County, IA, Humboldt County, IA, Iowa County, IA, Jackson County, IA, Jasper County, IA, Johnson County, IA, Jones County, IA, Linn County, IA, Marshall County, IA, Muscatine County, IA, Pocahontas County, IA, Polk County, IA, Poweshiek County, IA, Sac County, IA, Scott County, IA, Story County, IA, Tama County, IA, Webster County, IA, Wright County, IA, Carroll County, IL, Jo Daviess County, IL, Rock Island County, IL, Stephenson County, IL, Whiteside County, IL, Grant County, WI
The radar
The Des Moines radar (KDMX), 112 km from the middle of the area, began a volume at 18:53 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
- 40%
- One or more gusts of 65 knots or more
- 20%
- 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
18 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 24, 1:53 PM CDT | Severe Thunderstorm Warning | DMX | Black Hawk, Bremer | 67 min |
| Aug 24, 2:15 PM CDT | Severe Thunderstorm Warning | ARX | Chickasaw, Fayette | 60 min |
| Aug 24, 2:21 PM CDT | Severe Thunderstorm Warning | DVN | Buchanan | 39 min |
| Aug 24, 2:49 PM CDT | Severe Thunderstorm Warning | DVN | Benton, Buchanan, Delaware, Jones, Linn | 56 min |
| Aug 24, 2:59 PM CDT | Severe Thunderstorm Warning | ARX | Clayton, Fayette | 61 min |
| Aug 24, 3:03 PM CDT | Severe Thunderstorm Warning | DVN | Buchanan, Delaware, Dubuque | 42 min |
| Aug 24, 3:28 PM CDT | Severe Thunderstorm Warning | DMX | Hamilton, Hardin, Marshall, Story | 47 min |
| Aug 24, 3:35 PM CDT | Tornado Warning | ARX | Grant | 40 min |
| Aug 24, 3:38 PM CDT | Tornado Warning | DVN | Dubuque | 25 min |
| Aug 24, 3:42 PM CDT | Severe Thunderstorm Warning | DVN | Jo Daviess | 48 min |
| Aug 24, 4:03 PM CDT | Severe Thunderstorm Warning | DMX | Black Hawk, Grundy, Hardin, Marshall, Poweshiek, Tama | 57 min |
| Aug 24, 4:09 PM CDT | Severe Thunderstorm Warning | ARX | Grant | 36 min |
| Aug 24, 4:17 PM CDT | Severe Thunderstorm Warning | DVN | Jo Daviess, Stephenson | 58 min |
| Aug 24, 5:01 PM CDT | Severe Thunderstorm Warning | DVN | Carroll, Jo Daviess, Stephenson | 59 min |
| Aug 24, 5:05 PM CDT | Severe Thunderstorm Warning | DVN | Benton, Iowa | 40 min |
| Aug 24, 5:23 PM CDT | Severe Thunderstorm Warning | DVN | Carroll, Henry, Rock Island, Whiteside | 37 min |
| Aug 24, 5:46 PM CDT | Severe Thunderstorm Warning | DVN | Bureau, Henry, Mercer, Rock Island, Whiteside | 44 min |
| Aug 24, 6:07 PM CDT | Severe Thunderstorm Warning | DVN | Cedar, Johnson, Linn | 38 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, 6.9 hours before the alert went out and 226 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.
287 WWUS20 KWNS 241849 SEL1 SPC WW 241849 IAZ000-ILZ000-WIZ000-250000- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 461 NWS Storm Prediction Center Norman OK 150 PM CDT Tue Aug 24 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of northern Iowa northwestern Illinois southwestern Wisconsin * Effective this Tuesday afternoon and evening from 150 PM until 700 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...One or two clusters of thunderstorms may continue to evolve and organize through late afternoon, posing a risk for severe hail and damaging wind gusts as they spread east-southeastward across the region. The severe thunderstorm watch area is approximately along and 55 statute miles north and south of a line from 35 miles west of Fort Dodge IA to 40 miles east southeast of Dubuque IA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU1). 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. && 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 28035. ...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, 3:09 PM CDT | Mesoscale Discussion | SPC | Boone, McHenry, Ogle, Stephenson, Winnebago | 66 min |
| Aug 24, 3:55 PM CDT | Severe Thunderstorm Watch | SPC | Boone, Cook, DeKalb, DuPage, Kane, Lake and 4 more | 5 hr |
| Aug 24, 5:10 PM CDT | Mesoscale Discussion | SPC | Boone, Carroll, DeKalb, DuPage, Jo Daviess, Kane and 7 more | 2 hr |
| Aug 24, 12:44 PM CDT | Mesoscale Discussion | SPC | Allamakee, Bremer, Butler, Chickasaw, Clayton, Fayette and 4 more | 91 min |
| 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 |
Nearby
Severe Thunderstorm Watches in Iowa, 2021Severe 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.