Alert archive / South Dakota / Mesoscale Discussions in 2021

Mesoscale Discussion 1655

August 30, 202111 counties in Nebraska; 24 counties in South Dakota

The Storm Prediction Center issued this mesoscale discussion at Aug 30, 2021, 7:25 PM CDT for 11 counties in Nebraska; 24 counties in South Dakota. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: Aug 30, 2021, 7:25 PM CDT (00:25 UTC)
Expired: Aug 30, 2021, 10:00 PM CDT
In force: 3 hr
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 477

All 35 counties

Antelope County, NE, Boyd County, NE, Brown County, NE, Cedar County, NE, Cherry County, NE, Holt County, NE, Keya Paha County, NE, Knox County, NE, Pierce County, NE, Rock County, NE, Wayne County, NE, Aurora County, SD, Bennett County, SD, Bon Homme County, SD, Brule County, SD, Buffalo County, SD, Charles Mix County, SD, Clay County, SD, Davison County, SD, Douglas County, SD, Gregory County, SD, Haakon County, SD, Hughes County, SD, Hutchinson County, SD, Hyde County, SD, Jackson County, SD, Jerauld County, SD, Jones County, SD, Lyman County, SD, Mellette County, SD, Stanley County, SD, Sully County, SD, Todd County, SD, Tripp County, SD, Yankton County, SD

The radar

The North Platte radar (KLNX), 157 km from the middle of the area, began a volume at 00:28 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.

Severe Thunderstorm Watch 479Aug 30, 9:55 PM CDT

The nearest sounding before it

Aberdeen, SD (KABR), launched 00:00Z, 0.4 hours before the alert went out and 215 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 205 J/kg
Mixed-layer CIN: -60 J/kg
Mixed-layer LCL: 1953 m above ground
0-6 km bulk shear: 46 kt
0-1 km storm-relative helicity: 34 m²/s²
0-3 km storm-relative helicity: 126 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

As transmitted.

992 
ACUS11 KWNS 310025
SWOMCD
SPC MCD 310025 
NEZ000-SDZ000-310300-

Mesoscale Discussion 1655
NWS Storm Prediction Center Norman OK
0725 PM CDT Mon Aug 30 2021

Areas affected...portions of southern South Dakota and northern
Nebraska

Concerning...Severe Thunderstorm Watch 477...

Valid 310025Z - 310300Z

The severe weather threat for Severe Thunderstorm Watch 477
continues.

SUMMARY...Large hail and strong wind gusts will remain possible
across WW 477 the next few hours. A hail and damaging-wind threat
may develop downstream across parts of southern South Dakota and
northern Nebraska this evening and this area is being monitored for
possible watch issuance.

DISCUSSION...Isolated severe thunderstorms continue this evening
across western South Dakota within Severe Thunderstorm Watch 477.
Very large hail continues to be the main hazard with this activity
and should persist for another couple of hours. 

Downstream evolution of the severe threat continues to be somewhat
uncertain across parts of south-central/southeast SD and
north-central/northeast NE. An agitated CU field over Cherry County
NE has shown increasing vertical development over the past hour or
so, with several TCU noted in visible satellite imagery. HRRR
guidance has struggled to accurately depict ongoing convection
across the region in a weak forcing regime. But most guidance has
been consistent in developing east/southeastward-advancing
thunderstorm clusters across southern SD into northern NE this
evening. The 00z RAOB from LBF indicates inhibition has weakened
considerably since the 18z LBF RAOB. The overall environment
downstream from WW 477 remains favorable for severe storms given
strong vertical shear and moderate instability. A subtle shortwave
impulse shifting eastward from WY may be sufficient amid a
developing southerly low level jet across the region to support
additional thunderstorm development this evening. Coverage and
timing remains uncertain, but a downstream watch may be needed in
the next few hours downstream from WW 477.

..Leitman/Edwards.. 08/31/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...FSD...OAX...ABR...LBF...UNR...

LAT...LON   43580261 44210262 44750226 44980173 44840051 44529929
            43999833 43659782 43259725 42919697 42439694 42169716
            42019774 41979810 41979880 42020011 42190086 42630164
            43210232 43580261

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 30, 9:57 PM CDT	Severe Thunderstorm Watch	SPC	Antelope, Boone, Boyd, Brown, Burt, Butler and 24 more	7 hr
Aug 30, 11:35 PM CDT	Mesoscale Discussion	SPC	Burt, Butler, Cass, Colfax, Cuming, Dodge and 10 more	85 min
Aug 31, 3:02 AM CDT	Mesoscale Discussion	SPC	Antelope, Boone, Boyd, Brown, Burt, Butler and 32 more	118 min

Nearby

Mesoscale Discussions in South Dakota, 2021 Mesoscale Discussions in Nebraska, 2021 Every 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.