Mesoscale Discussion 1155

Issued

Jul 5, 2021, 1:34 PM CDT (18:34 UTC)

Expired

Jul 5, 2021, 3:30 PM CDT

In force

116 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The Rapid City radar (KUDX), 100 km from the middle of the area, began a volume at 18:38 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.

547 
ACUS11 KWNS 051834
SWOMCD
SPC MCD 051834 
SDZ000-NEZ000-MTZ000-WYZ000-052030-

Mesoscale Discussion 1155
NWS Storm Prediction Center Norman OK
0134 PM CDT Mon Jul 05 2021

Areas affected...portions of Montana Wyoming and South Dakota

Concerning...Severe potential...Watch possible 

Valid 051834Z - 052030Z

Probability of Watch Issuance...40 percent

SUMMARY...Isolated strong/severe storms will likely develop in
response to warm advection near a frontal zone across the High
Plains early this afternoon. Isolated instances of hail and damaging
winds will be possible. A better organized severe threat will likely
evolve across western portions of South Dakota this evening. A
weather watch is possible but uncertain in the short term.

DISCUSSION...Early afternoon water vapor imagery showed a weak vort
max traversing the central Rockies across portions of western
Wyoming. Ahead of this feature, several other weak disturbances
evident in lower-level imagery were crossing the Dakotas and High
Plains, where remnant morning convection and additional
boundary-layer cumulus have become more numerous in the past half
hour. Likely related to weak warm advection/forcing for ascent along
a diffuse frontal zone, this convection and additional storms should
track southeastward across South Dakota along the instability axis
(1500-2500 J/kg MUCAPE). On the fringes of stronger mid-level flow
aloft, vertical shear less than 30 kts should favor modestly
organized multicellar clusters. Likely rooted above the surface
given considerable MLCINH remaining on SPC mesoanalysis, these
storms/clusters will present mainly a risk for large hail initially,
before gradually becoming more surface based this afternoon/evening.


To the west northwest across portions of eastern Wyoming and the
Black Hills, boundary-layer cumulus was noted developing in a weak
upslope flow regime. As lift from the approaching trough and
orographic forcing continue to reduce inhibition, additional storms
should develop later this afternoon. With 1000-2000 J/kg of MLCAPE
and enhanced vertical shear around 30-35 kts ahead of the wave,
organized multicell clusters and perhaps a few supercells appear
likely to evolve. Damaging wind gusts and hail will be likely with
the strongest storms as they track to the east southeast into this
evening. Some upscale growth into one or more small MCS with a risk
of damaging winds into the overnight hours also appears probable.

Uncertainty remains high on the threat through the short term with
trends suggesting the potential for organized severe weather
remaining quite limited. The need for a weather watch appears more
likely later in the day for more robust convection developing to the
west. As such, convective trends will be monitored or a possible
weather watch this afternoon, though the need for a watch in the
short term remains uncertain.

..Lyons/Guyer.. 07/05/2021

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

ATTN...WFO...FSD...ABR...LBF...UNR...CYS...BYZ...

LAT...LON   45780418 45940374 45920304 45360141 44960038 44559938
            44019834 43749814 43349814 43079844 43039914 43029966
            42990029 42960140 43060371 43100429 43630466 44630464
            45260450 45780418

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