Alert archive / South Dakota / Mesoscale Discussions in 2021

Mesoscale Discussion 1622

August 27, 2021Butte County, Perkins County, Ziebach County, South Dakota

The Storm Prediction Center issued this mesoscale discussion at Aug 27, 2021, 5:33 PM MDT for Butte County, Perkins County, Ziebach County, South Dakota. It was in force for 117 min.

The area

The outline as issued.

The facts

Issued: Aug 27, 2021, 5:33 PM MDT (23:33 UTC)
Expired: Aug 27, 2021, 7:30 PM MDT
In force: 117 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Butte County, SD, Perkins County, SD, Ziebach County, SD

The nearest sounding before it

Rapid City, SD (KUNR), launched 12:00Z, 11.6 hours before the alert went out and 128 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: 112 J/kg
Mixed-layer CIN: -424 J/kg
Mixed-layer LCL: 757 m above ground
0-6 km bulk shear: 32 kt
0-1 km storm-relative helicity: -5 m²/s²
0-3 km storm-relative helicity: 141 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

349 
ACUS11 KWNS 272334
SWOMCD
SPC MCD 272333 
SDZ000-280130-

Mesoscale Discussion 1622
NWS Storm Prediction Center Norman OK
0633 PM CDT Fri Aug 27 2021

Areas affected...Northwestern South Dakota

Concerning...Severe potential...Watch unlikely 

Valid 272333Z - 280130Z

Probability of Watch Issuance...20 percent

SUMMARY...Large to very large-hail will be possible with a supercell
in northwest South Dakota. Damaging wind gusts are also possible.
Activity may persist for another 1-3 hours. A watch is not expected
unless storm coverage becomes greater than anticipated.

DISCUSSION...A supercell thunderstorm has intensified over the past
hour or so. GOES mesosector imagery has shown the development of a
back-sheared anvil and a more pronounced overshooting top. MRMS
CAPPI data have also indicated very high reflectivity aloft. With
over 50 kts of effective shear and the storm moving into a better
thermodynamic environment to the east, large to very large (2+ inch)
hail and damaging wind gusts will be threats. Storm coverage
continues to be the main question. Dry surface conditions have
limited buoyancy despite the mid-level ascent with a broad trough to
the northwest. Activity may persist a few hours into the evening
with support from an increasing low-level jet into central South
Dakota. A watch is not expected this evening given the isolated
coverage expected.

..Wendt/Bunting.. 08/27/2021

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

ATTN...WFO...ABR...UNR...

LAT...LON   45280401 45720310 45840205 45480149 44920141 44700229
            44820345 44960387 45280401

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 26, 6:25 PM MDT	Mesoscale Discussion	SPC	Aurora, Bennett, Bon Homme, Brule, Buffalo, Charles Mix and 22 more	2 hr
Aug 26, 7:03 PM MDT	Severe Thunderstorm Watch	SPC	Aurora, Beadle, Bennett, Bon Homme, Brookings, Brule and 36 more	7 hr
Aug 26, 9:45 PM MDT	Mesoscale Discussion	SPC	Union	2 hr
Aug 27, 2:55 PM MDT	Mesoscale Discussion	SPC	Butte, Harding, Perkins	2 hr

Nearby

Mesoscale Discussions in South Dakota, 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.