Alert archive / South Dakota / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 357
The Storm Prediction Center issued this severe thunderstorm watch at Jul 9, 2021, 5:33 PM MDT for 5 counties in South Dakota; Campbell County, Crook County, Weston County, Wyoming. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Jul 9, 2021, 5:33 PM MDT (23:33 UTC)
- Expired
- Jul 9, 2021, 9:44 PM MDT
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
Counties Custer County, SD, Fall River County, SD, Lawrence County, SD, Oglala Lakota County, SD, Pennington County, SD, Campbell County, WY, Crook County, WY, Weston County, WY
The radar
The Rapid City radar (KUDX), 149 km from the middle of the area, began a volume at 23:34 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
- 10%
- Six or more combined severe hail and wind reports
- 70%
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 |
|---|---|---|---|---|
| Jul 9, 5:41 PM MDT | Severe Thunderstorm Warning | UNR | Custer, Fall River, Oglala Lakota | 28 min |
| Jul 9, 6:15 PM MDT | Severe Thunderstorm Warning | UNR | Campbell, Weston | 60 min |
| Jul 9, 6:49 PM MDT | Severe Thunderstorm Warning | UNR | Crook, Weston | 41 min |
| Jul 9, 7:19 PM MDT | Severe Thunderstorm Warning | UNR | Weston | 41 min |
| Jul 9, 7:25 PM MDT | Severe Thunderstorm Warning | UNR | Custer, Pennington | 35 min |
| Jul 9, 7:57 PM MDT | Severe Thunderstorm Warning | UNR | Custer, Fall River | 63 min |
| Jul 9, 8:10 PM MDT | Severe Thunderstorm Warning | UNR | Fall River | 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
Rapid City, SD (KUNR), launched 12:00Z, 11.6 hours before the alert went out and 146 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
- 766 J/kg
- Mixed-layer CIN
- -307 J/kg
- Mixed-layer LCL
- 1363 m above ground
- 0-6 km bulk shear
- 34 kt
- 0-1 km storm-relative helicity
- 35 m²/s²
- 0-3 km storm-relative helicity
- 117 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.4
The text
As transmitted.
973 WWUS20 KWNS 092331 SEL7 SPC WW 092331 SDZ000-WYZ000-100500- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 357 NWS Storm Prediction Center Norman OK 535 PM MDT Fri Jul 9 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Southwest South Dakota Northeast Wyoming * Effective this Friday afternoon and evening from 535 PM until 1100 PM MDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Scattered large hail events to 1.5 inches in diameter possible SUMMARY...A small cluster with embedded supercells is expected to move east-southeastward across northeast Wyoming and southwest South Dakota this evening through early tonight. The strongest storms will be capable of producing occasional large hail and damaging outflow gusts. The severe thunderstorm watch area is approximately along and 40 statute miles north and south of a line from 25 miles west northwest of Gillette WY to 40 miles south southeast of Rapid City SD. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU7). 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 356... 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 450. Mean storm motion vector 30035. ...Thompson
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 8, 6:08 PM MDT | Mesoscale Discussion | SPC | Bennett, Haakon, Jackson, Meade, Oglala Lakota, Pennington and 2 more | 97 min |
| Jul 8, 7:54 PM MDT | Mesoscale Discussion | SPC | Aurora, Beadle, Brule, Buffalo, Campbell, Corson and 16 more | 2 hr |
| Jul 8, 8:33 PM MDT | Severe Thunderstorm Watch | SPC | Aurora, Beadle, Bon Homme, Brule, Buffalo, Charles Mix and 24 more | 5 hr |
| Jul 9, 1:41 AM MDT | Mesoscale Discussion | SPC | Aurora, Beadle, Bon Homme, Brule, Buffalo, Charles Mix and 27 more | 34 min |
| Jul 9, 1:38 PM MDT | Mesoscale Discussion | SPC | Goshen, Laramie, Platte | 97 min |
| Jul 9, 2:16 PM MDT | Severe Thunderstorm Watch | SPC | Goshen, Laramie, Niobrara, Platte | 9 hr |
| Jul 9, 2:20 PM MDT | Mesoscale Discussion | SPC | Campbell, Crook, Johnson, Sheridan, Weston | 85 min |
Nearby
Severe Thunderstorm Watches in South Dakota, 2021Severe Thunderstorm Watches in Wyoming, 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.