Mesoscale Discussion 1272

Issued

Jul 13, 2021, 2:21 PM MDT (20:21 UTC)

Expired

Jul 13, 2021, 3:45 PM MDT

In force

84 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...severe thunderstorm watch likely

Chance of a watch

95%

The Rapid City radar (KUDX), 206 km from the middle of the area, began a volume at 20:22 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.

• Severe Thunderstorm Watch 376Jul 13, 4:25 PM MDT

124 
ACUS11 KWNS 132021
SWOMCD
SPC MCD 132021 
NEZ000-SDZ000-MTZ000-WYZ000-132145-

Mesoscale Discussion 1272
NWS Storm Prediction Center Norman OK
0321 PM CDT Tue Jul 13 2021

Areas affected...Southern MT...Northeast WY...Western SD...Northwest
NE

Concerning...Severe potential...Severe Thunderstorm Watch likely 

Valid 132021Z - 132145Z

Probability of Watch Issuance...95 percent

SUMMARY...The severe thunderstorm threat will gradually increase
this afternoon, with isolated severe wind and hail possible. A more
substantial threat for damaging wind is expected to develop by early
evening. Watch issuance is likely for parts of the area by 21-22Z.

DISCUSSION...A well-defined midlevel shortwave trough is noted
across northwest MT at 20Z, with increasing cumulus and lightning
activity in advance of the shortwave across south-central MT and
north-central WY. Convection is expected to increase in coverage and
intensity this afternoon as it moves east-southeastward into an
increasingly unstable environment. Effective shear of 40+ kt will
support organized storm structures as convection matures, with
organized clusters and perhaps a supercell or two possible by late
afternoon, posing a threat of locally severe wind and hail. 

With time, convection is expected to evolve into a large cluster and
perhaps a well-organized MCS by early evening, as outflows
consolidate within an environment characterized by steep
low/midlevel lapse rates. As this occurs, the threat for more
widespread damaging wind will increase from northeast WY into the
Black Hills region of SD and Sand Hills region of NE, with some
gusts in excess of 65 kt possible. Severe Thunderstorm Watch
issuance for portions of the area is likely by 21-22Z.

..Dean/Dial.. 07/13/2021

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

ATTN...WFO...LBF...UNR...CYS...BYZ...RIW...

LAT...LON   46200904 45760657 45430530 45140429 44420280 43750228
            42720191 42240190 41910220 42010306 42080366 42220457
            42700589 43310718 44950934 45470918 45790913 46200904

Mesoscale Discussions in Wyoming, 2021Mesoscale Discussions in South Dakota, 2021Mesoscale Discussions in Montana, 2021Every mesoscale discussion in 2021

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.