Alert archive / Wisconsin / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 413
The Storm Prediction Center issued this severe thunderstorm watch at Aug 7, 2021, 4:36 PM CDT for 11 counties in Wisconsin. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 7, 2021, 4:36 PM CDT (21:36 UTC)
- Expired
- Aug 7, 2021, 9:00 PM CDT
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
Counties Columbia County, WI, Dane County, WI, Dodge County, WI, Green County, WI, Iowa County, WI, Jefferson County, WI, Lafayette County, WI, Rock County, WI, Sauk County, WI, Walworth County, WI, Waukesha County, WI
The radar
The Milwaukee radar (KMKX), 89 km from the middle of the area, began a volume at 21:39 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
- 20%
- One or more EF2 to EF5 tornadoes
- 5%
- Ten or more severe wind reports
- 60%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 50%
- One or more hailstones of 2 inches or more
- 20%
- Six or more combined severe hail and wind reports
- 90%
Warnings issued inside it
7 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 7, 4:38 PM CDT | Tornado Warning | MKX | Iowa | 67 min |
| Aug 7, 5:17 PM CDT | Severe Thunderstorm Warning | MKX | Columbia, Green Lake, Marquette, Sauk | 58 min |
| Aug 7, 5:26 PM CDT | Tornado Warning | MKX | Columbia | 39 min |
| Aug 7, 5:31 PM CDT | Severe Thunderstorm Warning | MKX | Columbia, Dane | 59 min |
| Aug 7, 5:33 PM CDT | Tornado Warning | MKX | Iowa | 57 min |
| Aug 7, 6:09 PM CDT | Severe Thunderstorm Warning | MKX | Dane | 66 min |
| Aug 7, 6:25 PM CDT | Severe Thunderstorm Warning | MKX | Dane | 50 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, 9.6 hours before the alert went out and 186 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
- 1645 J/kg
- Mixed-layer CIN
- -79 J/kg
- Mixed-layer LCL
- 1006 m above ground
- 0-6 km bulk shear
- 20 kt
- 0-1 km storm-relative helicity
- 39 m²/s²
- 0-3 km storm-relative helicity
- 37 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
387 WWUS20 KWNS 072130 SEL3 SPC WW 072130 WIZ000-080200- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 413 NWS Storm Prediction Center Norman OK 430 PM CDT Sat Aug 7 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Southern Wisconsin * Effective this Saturday afternoon and evening from 430 PM until 900 PM CDT. * Primary threats include... Scattered damaging wind gusts to 70 mph likely Scattered large hail events to 1.5 inches in diameter possible A tornado or two possible SUMMARY...A cluster of intense thunderstorms has developed over southwest Wisconsin. These storms will track eastward late this afternoon along a boundary, posing a risk of locally damaging wind gusts and hail. An isolated tornado or two is also possible. The severe thunderstorm watch area is approximately along and 35 statute miles north and south of a line from 10 miles southwest of Lonerock WI to 35 miles northeast of Janesville WI. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU3). 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 412... 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 29030. ...Hart
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 7, 11:03 AM CDT | Mesoscale Discussion | SPC | Crawford, Grant, Iowa, La Crosse, Richland, Sauk and 1 more | 2 hr |
| Aug 7, 3:46 PM CDT | Mesoscale Discussion | SPC | Columbia, Crawford, Dane, Grant, Green, Iowa and 5 more | 119 min |
| Aug 7, 5:02 PM CDT | Mesoscale Discussion | SPC | Green, Iowa, Rock, Walworth | 58 min |
Nearby
Severe 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.