Alert archive / Minnesota / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 452
The Storm Prediction Center issued this severe thunderstorm watch at Aug 20, 2021, 3:58 PM CDT for 22 counties in Iowa; 32 counties in Minnesota. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 20, 2021, 3:58 PM CDT (20:58 UTC)
- Expired
- Aug 20, 2021, 10:00 PM CDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 54 counties
Buena Vista County, IA, Calhoun County, IA, Carroll County, IA, Cherokee County, IA, Clay County, IA, Crawford County, IA, Dickinson County, IA, Emmet County, IA, Greene County, IA, Humboldt County, IA, Ida County, IA, Kossuth County, IA, Lyon County, IA, O'Brien County, IA, Osceola County, IA, Palo Alto County, IA, Plymouth County, IA, Pocahontas County, IA, Sac County, IA, Sioux County, IA, Webster County, IA, Woodbury County, IA, Big Stone County, MN, Blue Earth County, MN, Brown County, MN, Chippewa County, MN, Cottonwood County, MN, Douglas County, MN, Faribault County, MN, Jackson County, MN, Kandiyohi County, MN, Lac qui Parle County, MN, Lincoln County, MN, Lyon County, MN, Martin County, MN, McLeod County, MN, Meeker County, MN, Morrison County, MN, Murray County, MN, Nicollet County, MN, Nobles County, MN, Pipestone County, MN, Pope County, MN, Redwood County, MN, Renville County, MN, Rock County, MN, Sibley County, MN, Stearns County, MN, Stevens County, MN, Swift County, MN, Todd County, MN, Traverse County, MN, Watonwan County, MN, Yellow Medicine County, MN
The radar
The Minneapolis radar (KMPX), 126 km from the middle of the area, began a volume at 21:02 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
- 10%
- Ten or more severe wind reports
- 50%
- 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
- 10%
- Six or more combined severe hail and wind reports
- 80%
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 20, 4:54 PM CDT | Severe Thunderstorm Warning | MPX | Douglas | 19 min |
| Aug 20, 6:13 PM CDT | Severe Thunderstorm Warning | FSD | Cherokee, Plymouth, Woodbury | 32 min |
| Aug 20, 6:21 PM CDT | Severe Thunderstorm Warning | MPX | Pope, Stearns | 39 min |
| Aug 20, 6:31 PM CDT | Severe Thunderstorm Warning | FSD | Ida, Woodbury | 29 min |
| Aug 20, 6:53 PM CDT | Tornado Warning | MPX | Stearns | 37 min |
| Aug 20, 7:06 PM CDT | Severe Thunderstorm Warning | MPX | Morrison, Todd | 39 min |
| Aug 20, 9:46 PM CDT | Severe Thunderstorm Warning | DMX | Hamilton, Webster, Wright | 44 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
Minneapolis, MN (KMPX), launched 12:00Z, 9.0 hours before the alert went out and 123 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
- 48 J/kg
- Mixed-layer CIN
- -139 J/kg
- Mixed-layer LCL
- 999 m above ground
- 0-6 km bulk shear
- 20 kt
- 0-1 km storm-relative helicity
- 62 m²/s²
- 0-3 km storm-relative helicity
- 37 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
016 WWUS20 KWNS 202056 SEL2 SPC WW 202056 IAZ000-MNZ000-NEZ000-SDZ000-210300- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 452 NWS Storm Prediction Center Norman OK 400 PM CDT Fri Aug 20 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Northern Iowa Western Minnesota Northeast Nebraska Eastern South Dakota * Effective this Friday afternoon and evening from 400 PM until 1000 PM CDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Scattered large hail events to 1.5 inches in diameter possible A tornado or two possible SUMMARY...Storms are expected to develop and further intensify through late afternoon and early evening within multiple corridors across the region near and ahead (east) of an eastward-advancing cold front. The severe thunderstorm watch area is approximately along and 65 statute miles east and west of a line from 5 miles east northeast of Alexandria MN to 35 miles south of Storm Lake IA. 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 451... 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 550. Mean storm motion vector 23030. ...Guyer
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 20, 1:51 PM CDT | Mesoscale Discussion | SPC | Buena Vista, Cherokee, Crawford, Fremont, Harrison, Ida and 9 more | 84 min |
| Aug 20, 4:39 PM CDT | Severe Thunderstorm Watch | SPC | Fremont, Harrison, Mills, Monona, Montgomery, Page and 2 more | 6 hr |
| Aug 20, 1:41 PM CDT | Mesoscale Discussion | SPC | Clay, Kittson, Marshall, Norman, Pennington, Polk and 4 more | 3 hr |
| Aug 20, 2:24 PM CDT | Severe Thunderstorm Watch | SPC | Becker, Beltrami, Cass, Clay, Clearwater, Crow Wing and 16 more | 8 hr |
| Aug 20, 5:51 PM CDT | Mesoscale Discussion | SPC | Becker, Beltrami, Cass, Chippewa, Clearwater, Douglas and 20 more | 84 min |
Nearby
Severe Thunderstorm Watches in Minnesota, 2021Severe Thunderstorm Watches in Iowa, 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.