Alert archive / South Dakota / Severe Thunderstorm Watches in 2021

Severe Thunderstorm Watch 485

September 1, 20218 counties in Nebraska; 9 counties in South Dakota

The Storm Prediction Center issued this severe thunderstorm watch at Sep 1, 2021, 5:26 PM MDT for 8 counties in Nebraska; 9 counties in South Dakota. It was in force for 7 hr.

The area

The outline as issued.

The facts

Issued: Sep 1, 2021, 5:26 PM MDT (23:26 UTC)
Expired: Sep 2, 2021, 12:00 AM MDT
In force: 7 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1.5 in
Strongest gust expected: 60 kt

Counties Box Butte County, NE, Cherry County, NE, Dawes County, NE, Garden County, NE, Morrill County, NE, Scotts Bluff County, NE, Sheridan County, NE, Sioux County, NE, Bennett County, SD, Haakon County, SD, Jackson County, SD, Jones County, SD, Lyman County, SD, Mellette County, SD, Oglala Lakota County, SD, Todd County, SD, Tripp 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: 2%
Ten or more severe wind reports: 40%
One or more gusts of 65 knots or more: 10%
Ten or more severe hail reports: 50%
One or more hailstones of 2 inches or more: 10%
Six or more combined severe hail and wind reports: 80%

Warnings issued inside it

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

Issued	Product	Office	Counties	Lasted
Sep 1, 5:49 PM MDT	Severe Thunderstorm Warning	CYS	Box Butte, Morrill	41 min
Sep 1, 6:09 PM MDT	Severe Thunderstorm Warning	LBF	Garden, Sheridan	28 min
Sep 1, 10:30 PM MDT	Severe Thunderstorm Warning Considerable damage threat	LBF	Cherry, Sheridan	45 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, 11.4 hours before the alert went out and 157 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: 776 J/kg
Mixed-layer CIN: -479 J/kg
Mixed-layer LCL: 1980 m above ground
0-6 km bulk shear: 18 kt
0-1 km storm-relative helicity: 167 m²/s²
0-3 km storm-relative helicity: 132 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

963 
WWUS20 KWNS 012322
SEL5  
SPC WW 012322
NEZ000-SDZ000-020600-

URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 485
NWS Storm Prediction Center Norman OK
525 PM MDT Wed Sep 1 2021

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Western Nebraska
  Southwest and Central South Dakota

* Effective this Wednesday afternoon from 525 PM until Midnight
  MDT.

* 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...Thunderstorms are expected to increase in coverage and
intensity this evening from the Nebraska Panhandle/northwest
Nebraska northeastward into southwest/central South Dakota.
Instances of large hail and damaging winds will be possible.

The severe thunderstorm watch area is approximately along and 65
statute miles east and west of a line from 30 miles south southwest
of Alliance NE to 55 miles east northeast of Philip SD. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU5).

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 483...WW 484...

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
23020.

...Guyer

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 1, 4:39 PM MDT	Mesoscale Discussion	SPC	Box Butte, Dawes, Morrill, Sheridan	2 hr

Nearby

Severe Thunderstorm Watches in South Dakota, 2021 Severe Thunderstorm Watches in Nebraska, 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.