Alert archive / South Dakota / Mesoscale Discussions in 2021
Mesoscale Discussion 710
The Storm Prediction Center issued this mesoscale discussion at May 23, 2021, 12:58 PM MDT for 6 counties in South Dakota. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- May 23, 2021, 12:58 PM MDT (18:58 UTC)
- Expired
- May 23, 2021, 3:00 PM MDT
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch likely
- Chance of a watch
- 80%
Counties Haakon County, SD, Meade County, SD, Oglala Lakota County, SD, Pennington County, SD, Perkins County, SD, Ziebach County, SD
The radar
The Rapid City radar (KUDX), 49 km from the middle of the area, began a volume at 19:01 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
Rapid City, SD (KUNR), launched 12:00Z, 7.0 hours before the alert went out and 56 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 549 m above ground
- 0-6 km bulk shear
- 28 kt
- 0-1 km storm-relative helicity
- 271 m²/s²
- 0-3 km storm-relative helicity
- 339 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
603
ACUS11 KWNS 231859
SWOMCD
SPC MCD 231858
SDZ000-232100-
Mesoscale Discussion 0710
NWS Storm Prediction Center Norman OK
0158 PM CDT Sun May 23 2021
Areas affected...Parts of western South Dakota
Concerning...Severe potential...Watch likely
Valid 231858Z - 232100Z
Probability of Watch Issuance...80 percent
SUMMARY...Thunderstorms will develop east through north-northeast of
the Black Hills by 3-5 PM MDT, with the potential for a few to
intensify and pose increasing risk for severe hail, and perhaps a
couple of tornadoes.
DISCUSSION...A surface frontal zone, associated with the
southern/leading edge of shallow cold surface air, initially south
through east-northeast of the Black Hills, is eroding from southeast
to northwest. There is variance between the NAM and Rapid Refresh
concerning how this proceeds to the east and north-northeast of the
Black Hills through the remainder of the afternoon, as surface
pressures continue to fall across the high plains in response to a
couple of mid-level perturbations approaching the northern Rockies.
However, given potential for weak to moderate boundary-layer
destabilization, in the presence of strong (and strengthening)
deep-layer shear, the development of vigorous, organized convection
appears possible by 21-23Z. This may initially include supercells
posing a risk for severe hail, along with a conditional risk for
tornadoes.
..Kerr/Guyer.. 05/23/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...ABR...UNR...
LAT...LON 44320356 44950302 45580285 45850262 45690188 45010087
43500197 43150271 43060333 44320356SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 23, 10:53 AM MDT | Mesoscale Discussion | SPC | Fall River | 2 hr |
| May 23, 1:50 PM MDT | Tornado Watch | SPC | Bennett, Butte, Corson, Custer, Dewey, Fall River and 9 more | 7 hr |
| May 23, 1:57 PM MDT | Mesoscale Discussion | SPC | Fall River | 2 hr |
| May 23, 5:25 PM MDT | Mesoscale Discussion | SPC | Bennett, Butte, Corson, Custer, Dewey, Fall River and 9 more | 95 min |
Nearby
Mesoscale Discussions in South 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.