Alert archive / South Dakota / Mesoscale Discussions in 2021
Mesoscale Discussion 1426
The Storm Prediction Center issued this mesoscale discussion at Aug 6, 2021, 5:07 PM MDT for Cherry County, Dawes County, Sheridan County, Nebraska; 5 counties in South Dakota. It was in force for 113 min.
The area
The outline as issued.
The facts
- Issued
- Aug 6, 2021, 5:07 PM MDT (23:07 UTC)
- Expired
- Aug 6, 2021, 7:00 PM MDT
- In force
- 113 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 409
Counties Cherry County, NE, Dawes County, NE, Sheridan County, NE, Bennett County, SD, Jackson County, SD, Mellette County, SD, Oglala Lakota County, SD, Todd County, SD
The radar
The Rapid City radar (KUDX), 141 km from the middle of the area, began a volume at 23:08 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, 11.1 hours before the alert went out and 138 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
- 117 J/kg
- Mixed-layer CIN
- -465 J/kg
- Mixed-layer LCL
- 1438 m above ground
- 0-6 km bulk shear
- 29 kt
- 0-1 km storm-relative helicity
- 19 m²/s²
- 0-3 km storm-relative helicity
- 41 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
711
ACUS11 KWNS 062308
SWOMCD
SPC MCD 062307
NEZ000-SDZ000-070100-
Mesoscale Discussion 1426
NWS Storm Prediction Center Norman OK
0607 PM CDT Fri Aug 06 2021
Areas affected...Parts of southern South Dakota and northern
Nebraska
Concerning...Severe Thunderstorm Watch 409...
Valid 062307Z - 070100Z
The severe weather threat for Severe Thunderstorm Watch 409
continues.
SUMMARY...The evolution of an increasingly organized convective
system capable of producing severe hail and strong surface gusts in
excess of 50 kt appears possible near the South Dakota/Nebraska
vicinity, into the Valentine vicinity by 8-9 PM CDT. Trends are
being monitored for the possibility of a new severe weather watch
east of WW 409.
DISCUSSION...Stronger thunderstorm development may be consolidating
a bit west of Chadron NE, near/east of the Wyoming/South
Dakota/Nebraska border vicinity, aided by weak lower/mid level warm
advection ahead of an approaching short wave trough. This appears
focused along the southern periphery of a broad zone of strong
differential surface heating, beneath the northern/northeastern edge
of warmer and more strongly capping elevated mixed-layer air.
Near surface/low-level convergence also appears focused along the
zone, extending eastward along the South Dakota/Nebraska border
vicinity. Easterly low-level flow near and north of this boundary
is contributing to strong deep-layer shear beneath 30+ kt westerly
500 mb flow, while strongest and deepest boundary-layer mixing has
occurred along and to the south of the frontal zone.
Although mixed-layer CAPE is relatively modest to weak across the
higher plains to the west of Valentine, the environment may still be
conducive to the evolution of a gradually intensifying and
organizing thunderstorm cluster through 00-02Z. As this occurs,
there probably will be increasing potential for convection to
produce a swath of severe wind gusts in excess of 50 kt, as it
approaches the Valentine vicinity.
..Kerr.. 08/06/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LBF...UNR...CYS...
LAT...LON 43420327 43700181 43560022 42539995 42440103 42450212
42490327 42970322 43420327SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 6, 1:43 PM MDT | Severe Thunderstorm Watch | SPC | Dawes, Sioux | 6 hr |
| Aug 5, 8:34 PM MDT | Mesoscale Discussion | SPC | Clay, Lincoln, Minnehaha, Turner, Union | 86 min |
Nearby
Mesoscale Discussions in South Dakota, 2021Mesoscale Discussions in Nebraska, 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.