Alert archive / South Dakota / Mesoscale Discussions in 2021

Mesoscale Discussion 715

May 23, 2021Adams County, Bowman County, Sioux County, North Dakota; 15 counties in South Dakota; Niobrara County, Wyoming

The Storm Prediction Center issued this mesoscale discussion at May 23, 2021, 5:25 PM MDT for Adams County, Bowman County, Sioux County, North Dakota; 15 counties in South Dakota; Niobrara County, Wyoming. It was in force for 95 min.

The area

The outline as issued.

The facts

Issued: May 23, 2021, 5:25 PM MDT (23:25 UTC)
Expired: May 23, 2021, 7:00 PM MDT
In force: 95 min
Issued by: the Storm Prediction Center
Concerning: Tornado watch 197

Counties Adams County, ND, Bowman County, ND, Sioux County, ND, Bennett County, SD, Butte County, SD, Corson County, SD, Custer County, SD, Dewey County, SD, Fall River County, SD, Haakon County, SD, Harding County, SD, Jackson County, SD, Lawrence County, SD, Meade County, SD, Oglala Lakota County, SD, Pennington County, SD, Perkins County, SD, Ziebach County, SD, Niobrara County, WY

The radar

The Rapid City radar (KUDX), 24 km from the middle of the area, began a volume at 23:28 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 nearest sounding before it

Rapid City, SD (KUNR), launched 12:00Z, 11.4 hours before the alert went out and 30 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: 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

Open this sounding in Storm Lab

The text

As transmitted.

280 
ACUS11 KWNS 232326
SWOMCD
SPC MCD 232325 
SDZ000-NDZ000-WYZ000-240100-

Mesoscale Discussion 0715
NWS Storm Prediction Center Norman OK
0625 PM CDT Sun May 23 2021

Areas affected...Western South Dakota...Southwestern North Dakota

Concerning...Tornado Watch 197...

Valid 232325Z - 240100Z

The severe weather threat for Tornado Watch 197 continues.

SUMMARY...Severe threat continues across all but the southwestern
portions of ww197.

DISCUSSION...Surface warm front is advancing slowly north across
northwestern SD/southern ND early this evening. As a result,
buoyancy is gradually increasing across extreme southern ND where
surface temperatures have warmed into the lower 70s. One long-lived
supercell that matured earlier across western SD has lifted to near
Lemmon and will soon cross the warm front. This storm has produced a
few tornadoes over southeastern Perkins County SD, and until it
becomes elevated north of the warm front some tornado threat
remains. Otherwise, an arcing band of organized convection has
emerged from the northern Black Hills into northwestern NE. This
activity should continue surging northeast across the remainder of
southeastern/central portions of the watch, eventually spreading
toward the ND border later this evening. Tornado threat remains
highest with discrete supercells ahead of the squall line.

There is some concern that low-level warm advection will begin to
enhance the elevated convective threat north of the warm front over
western ND over the next few hours. Forecast soundings suggest hail
will be the biggest concern with this activity and some
consideration is being given for a potential severe thunderstorm
watch over this region.

..Darrow.. 05/23/2021

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

ATTN...WFO...ABR...BIS...UNR...CYS...

LAT...LON   43020461 46300361 46310023 43030147 43020461

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 23, 1:50 PM MDT	Tornado Watch	SPC	Adams, Grant, Hettinger, Sioux	7 hr
May 23, 10:53 AM MDT	Mesoscale Discussion	SPC	Fall River	2 hr
May 23, 12:58 PM MDT	Mesoscale Discussion	SPC	Haakon, Meade, Oglala Lakota, Pennington, Perkins, Ziebach	2 hr
May 23, 1:57 PM MDT	Mesoscale Discussion	SPC	Fall River	2 hr
May 23, 12:06 PM MDT	Tornado Watch	SPC	Goshen, Laramie, Niobrara	8 hr

Nearby

Mesoscale Discussions in South Dakota, 2021 Mesoscale Discussions in North Dakota, 2021 Mesoscale Discussions in Wyoming, 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.