Alert archive / South Dakota / Severe Thunderstorm Watches in 2021

Severe Thunderstorm Watch 411

August 6, 202115 counties in South Dakota

The Storm Prediction Center issued this severe thunderstorm watch at Aug 6, 2021, 10:08 PM CDT for 15 counties in South Dakota. It was in force for 4 hr.

The area

The outline as issued.

The facts

Issued: Aug 6, 2021, 10:08 PM CDT (03:08 UTC)
Expired: Aug 7, 2021, 2:34 AM CDT
In force: 4 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

Counties Aurora County, SD, Beadle County, SD, Bon Homme County, SD, Brule County, SD, Charles Mix County, SD, Davison County, SD, Douglas County, SD, Gregory County, SD, Hanson County, SD, Hutchinson County, SD, Jerauld County, SD, Kingsbury County, SD, McCook County, SD, Miner County, SD, Sanborn County, SD

The radar

The Sioux Falls radar (KFSD), 148 km from the middle of the area, began a volume at 03:11 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: 30%
One or more hailstones of 2 inches or more: 20%
Six or more combined severe hail and wind reports: 80%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Aug 6, 11:10 PM CDT	Severe Thunderstorm Warning	FSD	Brule	35 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

Aberdeen, SD (KABR), launched 00:00Z, 3.1 hours before the alert went out and 136 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: 466 J/kg
Mixed-layer CIN: -132 J/kg
Mixed-layer LCL: 1480 m above ground
0-6 km bulk shear: 19 kt
0-1 km storm-relative helicity: 113 m²/s²
0-3 km storm-relative helicity: 173 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

008 
WWUS20 KWNS 070306
SEL1  
SPC WW 070306
SDZ000-070900-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 411
NWS Storm Prediction Center Norman OK
1010 PM CDT Fri Aug 6 2021

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Southeast South Dakota

* Effective this Friday night and Saturday morning from 1010 PM
  until 400 AM CDT.

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

SUMMARY...A line of thunderstorms over south-central South Dakota
has been producing gusty/damaging wind gusts for the past couple of
hours.  These storms will track into the watch area with a continued
risk for severe wind gusts and perhaps hail.

The severe thunderstorm watch area is approximately along and 40
statute miles north and south of a line from 15 miles southwest of
Chamberlain SD to 50 miles east southeast of Mitchell SD. 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.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 410...

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, 7:21 PM CDT	Severe Thunderstorm Watch	SPC	Bennett, Buffalo, Hand, Hyde, Jackson, Jones and 4 more	6 hr
Aug 6, 9:09 PM CDT	Mesoscale Discussion	SPC	Aurora, Bon Homme, Brule, Buffalo, Charles Mix, Clay and 17 more	2 hr
Aug 6, 11:54 PM CDT	Mesoscale Discussion	SPC	Beadle, Clay, Davison, Hamlin, Hanson, Hutchinson and 10 more	2 hr
Aug 7, 2:10 AM CDT	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.