Alert archive / South Dakota / Mesoscale Discussions in 2021
Mesoscale Discussion 1678
The Storm Prediction Center issued this mesoscale discussion at Sep 1, 2021, 8:20 PM MDT for 8 counties in Nebraska; 9 counties in South Dakota. It was in force for 85 min.
The area
The outline as issued.
The facts
- Issued
- Sep 1, 2021, 8:20 PM MDT (02:20 UTC)
- Expired
- Sep 1, 2021, 9:45 PM MDT
- In force
- 85 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 485
Counties Box Butte County, NE, Cherry County, NE, Dawes County, NE, Garden County, NE, Morrill County, NE, Scotts Bluff County, NE, Sheridan County, NE, Sioux County, NE, Bennett County, SD, Haakon County, SD, Jackson County, SD, Jones County, SD, Lyman County, SD, Mellette County, SD, Oglala Lakota County, SD, Todd County, SD, Tripp County, SD
The radar
The North Platte radar (KLNX), 125 km from the middle of the area, began a volume at 02:22 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
Rapid City, SD (KUNR), launched 00:00Z, 2.3 hours before the alert went out and 177 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
- 549 J/kg
- Mixed-layer CIN
- -82 J/kg
- Mixed-layer LCL
- 1203 m above ground
- 0-6 km bulk shear
- 55 kt
- 0-1 km storm-relative helicity
- -34 m²/s²
- 0-3 km storm-relative helicity
- 71 m²/s²
- Significant tornado parameter
- -0.0
- Supercell composite
- -0.7
The text
As transmitted.
369
ACUS11 KWNS 020220
SWOMCD
SPC MCD 020220
SDZ000-NEZ000-020345-
Mesoscale Discussion 1678
NWS Storm Prediction Center Norman OK
0920 PM CDT Wed Sep 01 2021
Areas affected...western Nebraska and portions of southwest South
Dakota
Concerning...Severe Thunderstorm Watch 485...
Valid 020220Z - 020345Z
The severe weather threat for Severe Thunderstorm Watch 485
continues.
SUMMARY...Thunderstorms continue to increase in coverage across
Severe Thunderstorm Watch #485. The overall environment will support
a hail and wind threat through the evening.
DISCUSSION...Thunderstorms continue to develop across southern
portions of Severe Thunderstorm Watch #485, over portions of the
Nebraska Panhandle. Radar trends with these thunderstorms indicate
updrafts associated with these thunderstorms remain rather
pulse-like with episodic increases in the MRMS MESH flirting with
severe criteria at times, but otherwise generally remaining below
severe levels. This may be explained by by the strength of the
warm-air advection on the nose of the low-level jet. The continued
isentropic ascent is resulting in numerous thunderstorms that are
likely destructively interfering with one another causing individual
updrafts to struggle to maintain their initial intensity.
Despite current struggles for updrafts to maintain their initial
intensity, the overall background environment will remain supportive
of at least episodic severe potential given most-unstable CAPE
values between 1500-2000 J/kg and effective-layer shear greater than
35 knots. This is more than sufficient to pose a hail and wind
threat into the evening hours.
..Marsh.. 09/02/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...FSD...ABR...LBF...UNR...CYS...
LAT...LON 41720403 43010401 43020299 43600297 43680276 43680202
44510194 44730113 44180116 44179988 44059935 43839928
43679942 43519925 43489950 43019951 42970021 42100024
42060203 41760208 41730196 41410196 41410203 41240209
41220260 41420263 41430335 41670336 41720403SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Sep 1, 10:36 PM MDT | Mesoscale Discussion | SPC | Arthur, Cherry, Garden, Grant, Hooker, Sheridan | 84 min |
| Sep 2, 12:28 PM MDT | Mesoscale Discussion | SPC | Blaine, Brown, Buffalo, Custer, Dawson, Franklin and 13 more | 2 hr |
| Sep 2, 4:27 PM MDT | Tornado Watch | SPC | Adams, Buffalo, Butler, Clay, Dawson, Fillmore and 23 more | 5 hr |
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.