Alert archive / South Dakota / Severe Thunderstorm Watches in 2011
Severe Thunderstorm Watch 786
The Storm Prediction Center issued this severe thunderstorm watch at Aug 18, 2011, 4:45 PM CDT for 6 counties in North Dakota; 28 counties in South Dakota. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 18, 2011, 4:45 PM CDT (21:45 UTC)
- Expired
- Aug 18, 2011, 9:09 PM CDT
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 2.5 in
- Strongest gust expected
- 65 kt
All 34 counties
Dickey County, ND, Emmons County, ND, LaMoure County, ND, Logan County, ND, McIntosh County, ND, Sioux County, ND, Bennett County, SD, Brown County, SD, Buffalo County, SD, Campbell County, SD, Corson County, SD, Dewey County, SD, Edmunds County, SD, Faulk County, SD, Haakon County, SD, Hand County, SD, Hughes County, SD, Hyde County, SD, Jackson County, SD, Jones County, SD, Lyman County, SD, McPherson County, SD, Meade County, SD, Mellette County, SD, Pennington County, SD, Perkins County, SD, Potter County, SD, Spink County, SD, Stanley County, SD, Sully County, SD, Todd County, SD, Tripp County, SD, Walworth County, SD, Ziebach County, SD
The radar
The Rapid City radar (KUDX), 188 km from the middle of the area, began a volume at 21:45 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
- 20%
- One or more EF2 to EF5 tornadoes
- 5%
- Ten or more severe wind reports
- 50%
- 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
9 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 18, 4:55 PM CDT | Severe Thunderstorm Warning | UNR | Meade | 38 min |
| Aug 18, 5:06 PM CDT | Severe Thunderstorm Warning | UNR | Meade, Perkins, Ziebach | 54 min |
| Aug 18, 5:20 PM CDT | Severe Thunderstorm Warning | UNR | Bennett, Jackson | 55 min |
| Aug 18, 5:42 PM CDT | Severe Thunderstorm Warning | ABR | Campbell, Corson, Dewey, Walworth | 46 min |
| Aug 18, 6:07 PM CDT | Severe Thunderstorm Warning | UNR | Bennett | 53 min |
| Aug 18, 6:48 PM CDT | Severe Thunderstorm Warning | ABR | Potter, Walworth | 27 min |
| Aug 18, 6:52 PM CDT | Flash Flood Warning | ABR | Faulk, Hyde, Potter | 6 hr |
| Aug 18, 7:03 PM CDT | Severe Thunderstorm Warning | ABR | Potter | 27 min |
| Aug 18, 7:16 PM CDT | Severe Thunderstorm Warning | ABR | Faulk, Potter | 29 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 12:00Z, 9.8 hours before the alert went out and 192 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
- 1339 J/kg
- Mixed-layer CIN
- -177 J/kg
- Mixed-layer LCL
- 1070 m above ground
- 0-6 km bulk shear
- 40 kt
- 0-1 km storm-relative helicity
- 115 m²/s²
- 0-3 km storm-relative helicity
- 79 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.8
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 18, 3:43 PM CDT | Mesoscale Discussion | SPC | Barnes, Benson, Burleigh, Cass, Cavalier, Dickey and 27 more | 92 min |
| Aug 17, 9:18 PM CDT | Mesoscale Discussion | SPC | Mellette, Todd, Tripp | 57 min |
| Aug 18, 12:31 PM CDT | Mesoscale Discussion | SPC | Bon Homme, Clay, Hutchinson, Union, Yankton | 89 min |
| Aug 18, 1:27 PM CDT | Severe Thunderstorm Watch | SPC | Clay, Union, Yankton | 8 hr |
| Aug 18, 6:18 PM CDT | Mesoscale Discussion | SPC | Union | 27 min |
Nearby
Severe Thunderstorm Watches in South Dakota, 2011Severe Thunderstorm Watches in North Dakota, 2011Every severe thunderstorm watch in 2011
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.