Alert archive / Colorado / Mesoscale Discussions in 2026

Mesoscale Discussion 821

May 21, 20264 counties in Colorado; Kimball County, Nebraska

The Storm Prediction Center issued this mesoscale discussion at May 21, 2026, 5:16 PM MDT for 4 counties in Colorado; Kimball County, Nebraska. It was in force for 119 min.

The area

The outline as issued.

The facts

Issued: May 21, 2026, 5:16 PM MDT (23:16 UTC)
Expired: May 21, 2026, 7:15 PM MDT
In force: 119 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 239

Counties Kit Carson County, CO, Logan County, CO, Washington County, CO, Yuma County, CO, Kimball County, NE

The radar

The Denver radar (KFTG), 113 km from the middle of the area, began a volume at 23:17 UTC, the scan nearest the moment this went out.

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The text

As transmitted.

291 
ACUS11 KWNS 212316
SWOMCD
SPC MCD 212316 
KSZ000-COZ000-NEZ000-220115-

Mesoscale Discussion 0821
NWS Storm Prediction Center Norman OK
0616 PM CDT Thu May 21 2026

Areas affected...parts of southwestern Nebraska...northeast and east
central Colorado...adjacent northwestern Kansas

Concerning...Severe Thunderstorm Watch 239...

Valid 212316Z - 220115Z

The severe weather threat for Severe Thunderstorm Watch 239
continues.

SUMMARY...Isolated to widely scattered supercell development is
likely to persist through 6-8 PM MDT, accompanied by the risk for
large hail and perhaps some increase in potential for a tornado near
the Colorado/Kansas state border to the west-northwest of Goodland.

DISCUSSION...Isolated thunderstorm development has undergone notable
intensification the past few hours, aided by destabilization
associated with continued boundary-layer warming and moistening. 
This appears to have contributed to CAPE on the order of 1000-1500,
in the presence of strong westerly deep-layer shear, though with
mean ambient winds on the order of 20-30 kt, due to the veering of
winds with height.

Of the ongoing storms, the prominent supercell to the
north-northeast of Limon CO appears to have the longest access to
unstable inflow as it propagates eastward toward the Kansas state
border to the west-northwest of Goodland through 7-8 PM MDT.  It
appears that this may coincide with enlarging low-level hodographs
accompanying strengthening east-southeasterly 850 mb flow, which may
promote some further increase in potential for a tornado or two.

..Kerr.. 05/21/2026

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

ATTN...WFO...GLD...BOU...CYS...

LAT...LON   39890379 40800380 41420371 40840280 39750194 39040262
            39020312 39380365 39890379 

MOST PROBABLE PEAK TORNADO INTENSITY...85-110 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 21, 12:10 PM MDT	Mesoscale Discussion	SPC	Baca, Bent, Crowley, Huerfano, Kiowa, Las Animas and 3 more	2 hr
May 21, 1:19 PM MDT	Severe Thunderstorm Watch	SPC	Baca, Bent, Las Animas, Otero, Prowers	8 hr
May 21, 2:19 PM MDT	Mesoscale Discussion	SPC	Adams, Arapahoe, Elbert, Kit Carson, Logan, Morgan and 5 more	116 min
May 21, 2:55 PM MDT	Severe Thunderstorm Watch	SPC	Cheyenne, Elbert, Kit Carson, Lincoln, Logan, Morgan and 2 more	7 hr
May 21, 3:02 PM MDT	Mesoscale Discussion	SPC	Baca, Bent, Kiowa, Las Animas, Otero, Prowers	88 min

Nearby

Mesoscale Discussions in Colorado, 2026 Mesoscale Discussions in Nebraska, 2026 Every mesoscale discussion in 2026

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; radar from the NEXRAD Level II archive.