Alert archive / South Dakota / Severe Thunderstorm Watches in 2021

Severe Thunderstorm Watch 410

August 6, 202110 counties in South Dakota

The Storm Prediction Center issued this severe thunderstorm watch at Aug 6, 2021, 6:21 PM MDT for 10 counties in South Dakota. It was in force for 6 hr.

The area

The outline as issued.

The facts

Issued: Aug 6, 2021, 6:21 PM MDT (00:21 UTC)
Expired: Aug 7, 2021, 12:00 AM MDT
In force: 6 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

Counties Bennett County, SD, Buffalo County, SD, Hand County, SD, Hyde County, SD, Jackson County, SD, Jones County, SD, Lyman County, SD, Mellette County, SD, Todd County, SD, Tripp County, SD

The radar

The Rapid City radar (KUDX), 138 km from the middle of the area, began a volume at 00:20 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: 5%
One or more EF2 to EF5 tornadoes: 2%
Ten or more severe wind reports: 60%
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: 20%
Six or more combined severe hail and wind reports: 90%

Warnings issued inside it

8 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Aug 6, 6:53 PM MDT	Severe Thunderstorm Warning	UNR	Bennett, Jackson, Oglala Lakota	67 min
Aug 6, 7:06 PM MDT	Severe Thunderstorm Warning	UNR	Haakon, Jackson, Meade, Oglala Lakota, Pennington	54 min
Aug 6, 7:56 PM MDT	Severe Thunderstorm Warning	UNR	Bennett, Jackson, Mellette, Todd	64 min
Aug 6, 8:30 PM MDT	Severe Thunderstorm Warning	UNR	Mellette, Todd, Tripp	75 min
Aug 6, 9:42 PM MDT	Severe Thunderstorm Warning	UNR	Tripp	34 min
Aug 6, 10:07 PM MDT	Severe Thunderstorm Warning	ABR	Buffalo, Lyman	38 min
Aug 6, 10:29 PM MDT	Severe Thunderstorm Warning	ABR	Buffalo, Hand, Hyde, Lyman	46 min
Aug 6, 11:10 PM MDT	Severe Thunderstorm Warning Considerable damage threat	ABR	Faulk, Hand, Hyde, Spink	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 00:00Z, 0.4 hours before the alert went out and 140 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 624 J/kg
Mixed-layer CIN: -211 J/kg
Mixed-layer LCL: 2013 m above ground
0-6 km bulk shear: 26 kt
0-1 km storm-relative helicity: 8 m²/s²
0-3 km storm-relative helicity: 48 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

405 
WWUS20 KWNS 070017
SEL0  
SPC WW 070017
SDZ000-070600-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 410
NWS Storm Prediction Center Norman OK
720 PM CDT Fri Aug 6 2021

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  South Central South Dakota

* Effective this Friday night and Saturday morning from 720 PM
  until 100 AM CDT.

* Primary threats include...
  Scattered damaging wind gusts to 70 mph likely
  Scattered large hail events to 1.5 inches in diameter possible

SUMMARY...A cluster of thunderstorms over southwest South Dakota
will track eastward across the watch area this evening, posing a
risk of locally damaging wind gusts and hail.

The severe thunderstorm watch area is approximately along and 50
statute miles north and south of a line from 50 miles southwest of
Philip SD to 70 miles northeast of Valentine NE. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU0).

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 409...

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
26035.

...Hart

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 6, 8:09 PM MDT	Mesoscale Discussion	SPC	Boyd, Cedar, Keya Paha, Knox	2 hr
Aug 7, 5:11 PM MDT	Mesoscale Discussion	SPC	Clay, Fillmore, Gage, Jefferson, Lancaster, Nuckolls and 3 more	2 hr
Aug 7, 5:35 PM MDT	Severe Thunderstorm Watch	SPC	Adams, Butler, Cass, Clay, Colfax, Dodge and 26 more	6 hr
Aug 6, 9:08 PM MDT	Severe Thunderstorm Watch	SPC	Aurora, Beadle, Bon Homme, Brule, Charles Mix, Davison and 9 more	4 hr
Aug 6, 10:54 PM MDT	Mesoscale Discussion	SPC	Beadle, Clay, Davison, Hamlin, Hanson, Hutchinson and 10 more	2 hr
Aug 7, 1:10 AM MDT	Mesoscale Discussion	SPC	Brookings, Clark, Codington, Day, Deuel, Grant and 3 more	2 hr

Nearby

Severe Thunderstorm Watches in South Dakota, 2021 Every 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.