Alert archive / South Dakota / Mesoscale Discussions in 2021
Mesoscale Discussion 1428
The Storm Prediction Center issued this mesoscale discussion at Aug 6, 2021, 11:54 PM CDT for Lyon County, Sioux County, Iowa; Rock County, Minnesota; 16 counties in South Dakota. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 6, 2021, 11:54 PM CDT (04:54 UTC)
- Expired
- Aug 7, 2021, 2:00 AM CDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 411
Counties Lyon County, IA, Sioux County, IA, Rock County, MN, Beadle County, SD, Clay County, SD, Davison County, SD, Hamlin County, SD, Hanson County, SD, Hutchinson County, SD, Jerauld County, SD, Kingsbury County, SD, Lake County, SD, Lincoln County, SD, McCook County, SD, Miner County, SD, Minnehaha County, SD, Sanborn County, SD, Turner County, SD, Yankton County, SD
The radar
The Sioux Falls radar (KFSD), 80 km from the middle of the area, began a volume at 04:58 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.
The nearest sounding before it
Aberdeen, SD (KABR), launched 00:00Z, 4.9 hours before the alert went out and 128 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
- 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
The text
As transmitted.
794
ACUS11 KWNS 070455
SWOMCD
SPC MCD 070454
MNZ000-IAZ000-SDZ000-070700-
Mesoscale Discussion 1428
NWS Storm Prediction Center Norman OK
1154 PM CDT Fri Aug 06 2021
Areas affected...Parts of southern/eastern South Dakota
Concerning...Severe Thunderstorm Watch 411...
Valid 070454Z - 070700Z
The severe weather threat for Severe Thunderstorm Watch 411
continues.
SUMMARY...Strong wind gusts continue, but may gradually begin to
wane with storms spreading north of Chamberlain, toward the Huron
area, during the next few hours. At least scattered strong new
thunderstorms may continue to develop near the Interstate 90
corridor around Sioux Falls through 1-2 AM CDT.
DISCUSSION...Strongest recent thunderstorm development has been
focused in a small cluster near the nose of a north-northeastward
surging rear inflow jet which spread across the Valentine NE/Winner
SD area earlier this evening. This has reached areas of south
central South Dakota between Pierre and Chamberlain, where various
wind sensors continue to indicate strong to severe surface gusts,
but this may gradually wane as convection progresses into less
unstable environment near/north of Huron by 06-07Z.
Strongest boundary-layer instability, steepest lower/mid
tropospheric lapse rates and strongest shear remain focused along a
remnant baroclinic zone slowly shifting north of the eastern
Nebraska /South Dakota border area. With a nocturnally
strengthening low-level jet focusing increasing lift associated with
warm advection along this boundary, at least scattered vigorous new
thunderstorm development may begin to initiate during the next few
hours.
..Kerr.. 08/07/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...FSD...ABR...
LAT...LON 44869900 44829719 44049673 43589589 42949615 42819690
43199820 43599835 44179897 44869900SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 7, 2:10 AM CDT | Mesoscale Discussion | SPC | Lyon, Osceola | 2 hr |
| Aug 7, 11:03 AM CDT | Mesoscale Discussion | SPC | Allamakee, Black Hawk, Bremer, Buchanan, Butler, Cerro Gordo and 11 more | 2 hr |
| Aug 7, 3:46 PM CDT | Mesoscale Discussion | SPC | Allamakee, Bremer, Butler, Cerro Gordo, Chickasaw, Clayton and 7 more | 119 min |
| Aug 7, 6:35 PM CDT | Severe Thunderstorm Watch | SPC | Fremont, Harrison, Mills, Montgomery, Page, Pottawattamie and 1 more | 6 hr |
| 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, 10:08 PM CDT | Severe Thunderstorm Watch | SPC | Aurora, Beadle, Bon Homme, Brule, Charles Mix, Davison and 9 more | 4 hr |
Nearby
Mesoscale Discussions in South Dakota, 2021Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Minnesota, 2021Every mesoscale discussion 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.