Alert archive / Nebraska / Mesoscale Discussions in 2021

Mesoscale Discussion 1525

August 14, 202110 counties in Nebraska; 6 counties in South Dakota

The Storm Prediction Center issued this mesoscale discussion at Aug 14, 2021, 12:50 PM MDT for 10 counties in Nebraska; 6 counties in South Dakota. It was in force for 115 min.

The area

The outline as issued.

The facts

Issued: Aug 14, 2021, 12:50 PM MDT (18:50 UTC)
Expired: Aug 14, 2021, 2:45 PM MDT
In force: 115 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 40%

Counties Arthur County, NE, Box Butte County, NE, Cherry County, NE, Dawes County, NE, Garden County, NE, Grant County, NE, Hooker County, NE, McPherson County, NE, Morrill County, NE, Sheridan County, NE, Bennett County, SD, Custer County, SD, Fall River County, SD, Jackson County, SD, Oglala Lakota County, SD, Pennington County, SD

The radar

The Rapid City radar (KUDX), 154 km from the middle of the area, began a volume at 18:54 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 440Aug 14, 3:25 PM MDT

The nearest sounding before it

Rapid City, SD (KUNR), launched 12:00Z, 6.8 hours before the alert went out and 150 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: 911 J/kg
Mixed-layer CIN: -150 J/kg
Mixed-layer LCL: 1691 m above ground
0-6 km bulk shear: 25 kt
0-1 km storm-relative helicity: 93 m²/s²
0-3 km storm-relative helicity: 90 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 1.7

Open this sounding in Storm Lab

The text

As transmitted.

828 
ACUS11 KWNS 141850
SWOMCD
SPC MCD 141850 
NEZ000-SDZ000-142045-

Mesoscale Discussion 1525
NWS Storm Prediction Center Norman OK
0150 PM CDT Sat Aug 14 2021

Areas affected...portions of southwest SD into western NE

Concerning...Severe potential...Watch possible 

Valid 141850Z - 142045Z

Probability of Watch Issuance...40 percent

SUMMARY...Isolated storms capable of hail and damaging wind gusts
are possible this afternoon and evening.

DISCUSSION...Isolated convection is developing near the southern
portion of the Black Hills in Custer County SD this afternoon. While
large-scale ascent remains modest over the region, this activity is
likely being aided by orographic influences as strong heating has
weakened capping over the region and instability has increased to
1500-2000 J/kg MLCAPE. Additional cumulus is developing across the
broader region amid weak warm advection/southerly low level flow.
Moderate mid/upper level northwesterly flow atop southerly low level
winds is resulting in 35-45 kt effective shear. Midlevel lapse rates
also are expected to continue steepening through this evening. This
should result in some organized storm structures capable of
producing hail. Furthermore, steep low level lapse rates and large
temperature-dewpoint spread will promote strong to severe wind
gusts. 

Given subtle forcing and HRRR guidance notably lacking convection
compared to other CAMs guidance, there is some uncertainty regarding
coverage and timing of convection. While the overall environment
will support severe storms, convective trends will continue to be
monitored for possible watch issuance should coverage increase
sufficiently this afternoon.

..Leitman/Hart.. 08/14/2021

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

ATTN...WFO...LBF...UNR...CYS...

LAT...LON   44110311 44190239 44030183 42830069 41920050 41470098
            41270185 41320259 41660307 42440332 43010356 43800348
            44110311

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Aug 14, 3:28 PM MDT	Severe Thunderstorm Watch	SPC	Arthur, Banner, Box Butte, Chase, Cherry, Cheyenne and 19 more	7 hr

Nearby

Mesoscale Discussions in Nebraska, 2021 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; radar from the NEXRAD Level II archive.