Alert archive / Minnesota / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 451
The Storm Prediction Center issued this severe thunderstorm watch at Aug 20, 2021, 2:24 PM CDT for 22 counties in Minnesota; 17 counties in North Dakota. It was in force for 8 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 20, 2021, 2:24 PM CDT (19:24 UTC)
- Expired
- Aug 20, 2021, 10:00 PM CDT
- In force
- 8 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 39 counties
Becker County, MN, Beltrami County, MN, Cass County, MN, Clay County, MN, Clearwater County, MN, Crow Wing County, MN, Grant County, MN, Hubbard County, MN, Itasca County, MN, Kittson County, MN, Koochiching County, MN, Lake of the Woods County, MN, Mahnomen County, MN, Marshall County, MN, Norman County, MN, Otter Tail County, MN, Pennington County, MN, Polk County, MN, Red Lake County, MN, Roseau County, MN, Wadena County, MN, Wilkin County, MN, Barnes County, ND, Cass County, ND, Eddy County, ND, Foster County, ND, Grand Forks County, ND, Griggs County, ND, LaMoure County, ND, Nelson County, ND, Pembina County, ND, Ramsey County, ND, Ransom County, ND, Richland County, ND, Sargent County, ND, Steele County, ND, Stutsman County, ND, Traill County, ND, Walsh County, ND
The radar
The Fargo/Grand Forks radar (KMVX), 116 km from the middle of the area, began a volume at 19:25 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
- 40%
- One or more hailstones of 2 inches or more
- 10%
- Six or more combined severe hail and wind reports
- 80%
Warnings issued inside it
6 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 20, 2:43 PM CDT | Tornado Warning | FGF | Barnes, Cass | 47 min |
| Aug 20, 4:11 PM CDT | Tornado Warning | FGF | Barnes, Griggs, Steele | 49 min |
| Aug 20, 4:13 PM CDT | Tornado Warning | FGF | Cass, Traill | 47 min |
| Aug 20, 4:49 PM CDT | Severe Thunderstorm Warning | FGF | Norman, Polk | 26 min |
| Aug 20, 5:07 PM CDT | Severe Thunderstorm Warning | FGF | Otter Tail, Wadena | 38 min |
| Aug 20, 5:13 PM CDT | Severe Thunderstorm Warning | FGF | Pennington, Polk, Red Lake | 39 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
International Fa, MN (KINL), launched 12:00Z, 7.4 hours before the alert went out and 207 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
- 347 J/kg
- Mixed-layer CIN
- -74 J/kg
- Mixed-layer LCL
- 1086 m above ground
- 0-6 km bulk shear
- 29 kt
- 0-1 km storm-relative helicity
- 22 m²/s²
- 0-3 km storm-relative helicity
- 13 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
287 WWUS20 KWNS 201921 SEL1 SPC WW 201921 MNZ000-NDZ000-210300- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 451 NWS Storm Prediction Center Norman OK 225 PM CDT Fri Aug 20 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Northern Minnesota Eastern North Dakota * Effective this Friday afternoon and evening from 225 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...A line of strong to severe thunderstorms will continue to move east-northeastward across northern Minnesota this afternoon, while additional severe storms are expected to develop across eastern North Dakota, potentially including some fast northeastward-moving supercells. The severe thunderstorm watch area is approximately along and 120 statute miles east and west of a line from 30 miles west northwest of Roseau MN to 65 miles south southwest of Detroit Lakes MN. 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 550. Mean storm motion vector 21035. ...Guyer
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 20, 1:41 PM CDT | Mesoscale Discussion | SPC | Clay, Kittson, Marshall, Norman, Pennington, Polk and 4 more | 3 hr |
| Aug 20, 3:58 PM CDT | Severe Thunderstorm Watch | SPC | Big Stone, Blue Earth, Brown, Chippewa, Cottonwood, Douglas and 26 more | 6 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 North Dakota, 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.