Alert archive / South Dakota / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 477
The Storm Prediction Center issued this severe thunderstorm watch at Aug 30, 2021, 3:03 PM MDT for 19 counties in South Dakota. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 30, 2021, 3:03 PM MDT (21:03 UTC)
- Expired
- Aug 30, 2021, 9:00 PM MDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2.5 in
- Strongest gust expected
- 65 kt
Counties Bennett County, SD, Campbell County, SD, Corson County, SD, Custer County, SD, Dewey County, SD, Haakon County, SD, Hughes County, SD, Jackson County, SD, Jones County, SD, Lawrence County, SD, Meade County, SD, Oglala Lakota County, SD, Pennington County, SD, Perkins County, SD, Potter County, SD, Stanley County, SD, Sully County, SD, Walworth County, SD, Ziebach County, SD
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
- 30%
- One or more gusts of 65 knots or more
- 30%
- Ten or more severe hail reports
- 40%
- One or more hailstones of 2 inches or more
- 40%
- Six or more combined severe hail and wind reports
- 70%
Warnings issued inside it
16 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 30, 3:34 PM MDT | Severe Thunderstorm Warning | UNR | Perkins | 56 min |
| Aug 30, 3:54 PM MDT | Severe Thunderstorm Warning | ABR | Corson | 51 min |
| Aug 30, 4:09 PM MDT | Severe Thunderstorm Warning | UNR | Custer, Pennington | 66 min |
| Aug 30, 4:29 PM MDT | Severe Thunderstorm Warning | UNR | Perkins | 61 min |
| Aug 30, 4:44 PM MDT | Severe Thunderstorm Warning | ABR | Corson | 46 min |
| Aug 30, 4:58 PM MDT | Severe Thunderstorm Warning | UNR | Custer | 62 min |
| Aug 30, 5:06 PM MDT | Severe Thunderstorm Warning | UNR | Perkins, Ziebach | 54 min |
| Aug 30, 5:45 PM MDT | Severe Thunderstorm Warning | UNR | Meade, Perkins, Ziebach | 60 min |
| Aug 30, 5:50 PM MDT | Severe Thunderstorm Warning | UNR | Custer, Fall River, Oglala Lakota | 36 min |
| Aug 30, 5:53 PM MDT | Severe Thunderstorm Warning | UNR | Perkins | 67 min |
| Aug 30, 6:42 PM MDT | Severe Thunderstorm Warning | UNR | Meade, Perkins, Ziebach | 63 min |
| Aug 30, 6:56 PM MDT | Severe Thunderstorm Warning | UNR | Perkins | 64 min |
| Aug 30, 7:41 PM MDT | Severe Thunderstorm Warning | UNR | Haakon, Meade, Ziebach | 64 min |
| Aug 30, 8:30 PM MDT | Severe Thunderstorm Warning | UNR | Meade, Pennington | 60 min |
| Aug 30, 8:40 PM MDT | Severe Thunderstorm Warning | UNR | Ziebach | 40 min |
| Aug 30, 8:46 PM MDT | Severe Thunderstorm Warning | UNR | Haakon, Ziebach | 59 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, 9.1 hours before the alert went out and 147 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
- 1072 J/kg
- Mixed-layer CIN
- -169 J/kg
- Mixed-layer LCL
- 1286 m above ground
- 0-6 km bulk shear
- 29 kt
- 0-1 km storm-relative helicity
- 18 m²/s²
- 0-3 km storm-relative helicity
- 61 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- -0.7
The text
As transmitted.
401
WWUS20 KWNS 302101
SEL7
SPC WW 302101
SDZ000-310300-
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 477
NWS Storm Prediction Center Norman OK
305 PM MDT Mon Aug 30 2021
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Westner to central South Dakota
* Effective this Monday afternoon and evening from 305 PM until
900 PM MDT.
* Primary threats include...
Scattered large hail and isolated very large hail events to 2.5
inches in diameter possible
Isolated significant damaging wind gusts to 75 mph possible
A tornado or two possible
SUMMARY...A couple supercells may develop from the Black Hills to
the South Dakota-North Dakota border area this evening.
The severe thunderstorm watch area is approximately along and 60
statute miles east and west of a line from 40 miles northwest of
Mobridge SD to 55 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 475...WW 476...
AVIATION...A few severe thunderstorms with hail surface and aloft to
2.5 inches. Extreme turbulence and surface wind gusts to 65 knots. A
few cumulonimbi with maximum tops to 550. Mean storm motion vector
32025.
...GramsSPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 30, 1:50 PM MDT | Mesoscale Discussion | SPC | Bennett, Custer, Fall River, Jackson, Lawrence, Meade and 2 more | 115 min |
| Aug 30, 1:54 PM MDT | Mesoscale Discussion | SPC | Campbell, Corson | 2 hr |
Nearby
Severe Thunderstorm Watches in South 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.