Alert archive / South Dakota / Mesoscale Discussions in 2021
Mesoscale Discussion 1584
The Storm Prediction Center issued this mesoscale discussion at Aug 23, 2021, 9:37 PM CDT for Boyd County, Keya Paha County, Nebraska; Sioux County, North Dakota; 27 counties in South Dakota. It was in force for 113 min.
The area
The outline as issued.
The facts
- Issued
- Aug 23, 2021, 9:37 PM CDT (02:37 UTC)
- Expired
- Aug 23, 2021, 11:30 PM CDT
- In force
- 113 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 458
All 30 counties
Sioux County, ND, Boyd County, NE, Keya Paha County, NE, Aurora County, SD, Beadle County, SD, Brule County, SD, Buffalo County, SD, Campbell County, SD, Charles Mix County, SD, Corson County, SD, Davison County, SD, Dewey County, SD, Douglas County, SD, Edmunds County, SD, Faulk County, SD, Gregory County, SD, Hand County, SD, Hughes County, SD, Hyde County, SD, Jerauld County, SD, Jones County, SD, Lyman County, SD, McPherson County, SD, Potter County, SD, Sanborn County, SD, Spink County, SD, Stanley County, SD, Sully County, SD, Tripp County, SD, Walworth County, SD
The radar
The Aberdeen radar (KABR), 156 km from the middle of the area, began a volume at 02:37 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Aberdeen, SD (KABR), launched 00:00Z, 2.6 hours before the alert went out and 120 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
- 142 J/kg
- Mixed-layer CIN
- -222 J/kg
- Mixed-layer LCL
- 2124 m above ground
- 0-6 km bulk shear
- 46 kt
- 0-1 km storm-relative helicity
- 173 m²/s²
- 0-3 km storm-relative helicity
- 342 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 1.1
The text
As transmitted.
348
ACUS11 KWNS 240237
SWOMCD
SPC MCD 240237
SDZ000-NEZ000-NDZ000-240430-
Mesoscale Discussion 1584
NWS Storm Prediction Center Norman OK
0937 PM CDT Mon Aug 23 2021
Areas affected...South Dakota into far southern North Dakota
Concerning...Severe Thunderstorm Watch 458...
Valid 240237Z - 240430Z
The severe weather threat for Severe Thunderstorm Watch 458
continues.
SUMMARY...The greatest near-term severe risk will reside along the
ND/SD border over the next 1-2 hours. The environment remains
favorable for strong to severe storms across WW 458, but the threat
is becoming more conditional.
DISCUSSION...Prior convection across the western portion of WW 458
has shown a steady weakening trend over the past hour. This is
likely the result of diurnally increasing inhibition on the fringe
of better ascent to the north/northwest. The probability of new
convection developing over south-central SD appears to be
diminishing, and WW 458 may be canceled early due to this decreasing
potential. However, the environment remains conditionally favorable
for organized storms with 2000-3000 J/kg MLCAPE and 40-50 knots of
effective bulk shear. Convection initiating along a dryline across
the NE Panhandle may propagate into this environment and intensify
in the coming hours, but confidence in this scenario is sufficiently
low to warrant watch cancellation.
Along the ND/SD border, strong to severe thunderstorms have
developed within a theta-e advection maxima in the 925-850 mb layer.
The environment along the ND/SD border should remain favorable for
organized convection over the coming hours thanks to continued
moisture advection into the region and persistent strong flow aloft.
Latest short-term guidance suggests this zone of ascent should
reside within this environment at least for the next 1-2 hours
before shifting northward into central ND where thermodynamic
profiles are less favorable.
..Moore.. 08/24/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...FSD...OAX...ABR...BIS...LBF...UNR...
LAT...LON 43050030 43940100 44830157 45520168 46070140 46280061
46179961 45629894 44809814 43899793 43209775 42849820
42769939 43050030SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 24, 6:00 PM CDT | Mesoscale Discussion | SPC | Antelope, Blaine, Boone, Brown, Butler, Colfax and 22 more | 2 hr |
| Aug 23, 7:38 PM CDT | Mesoscale Discussion | SPC | Emmons, Grant, Logan, McIntosh, Sioux | 2 hr |
| Aug 23, 10:11 PM CDT | Severe Thunderstorm Watch | SPC | Dickey, Emmons, LaMoure, Logan, McIntosh, Ransom and 3 more | 5 hr |
| Aug 23, 11:32 PM CDT | Mesoscale Discussion | SPC | Dickey, Emmons, McIntosh, Richland, Sargent | 118 min |
Nearby
Mesoscale Discussions in South Dakota, 2021Mesoscale Discussions in Nebraska, 2021Mesoscale Discussions in North Dakota, 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.