Mesoscale Discussion 1157

Issued

Jul 5, 2021, 5:44 PM CDT (22:44 UTC)

Expired

Jul 5, 2021, 7:45 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

5%

Counties Buena Vista County, IA, Cherokee County, IA, Clay County, IA, Hancock County, IA, Humboldt County, IA, Kossuth County, IA, Lyon County, IA, O'Brien County, IA, Osceola County, IA, Palo Alto County, IA, Plymouth County, IA, Pocahontas County, IA, Sioux County, IA, Webster County, IA, Wright County, IA, Clay County, SD, Lincoln County, SD, Turner County, SD, Union County, SD, Yankton County, SD

The Sioux Falls radar (KFSD), 92 km from the middle of the area, began a volume at 22:43 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.

752 
ACUS11 KWNS 052244
SWOMCD
SPC MCD 052244 
IAZ000-MNZ000-SDZ000-NEZ000-060045-

Mesoscale Discussion 1157
NWS Storm Prediction Center Norman OK
0544 PM CDT Mon Jul 05 2021

Areas affected...Far southeast South Dakota into northwest Iowa

Concerning...Severe potential...Watch unlikely 

Valid 052244Z - 060045Z

Probability of Watch Issuance...5 percent

SUMMARY...Thunderstorms may develop along a stationary boundary
across northwest to north-central Iowa prior to sunset, though the
potential for additional storms is uncertain. However, storms that
do form could pose a brief severe hail risk.

DISCUSSION...Recent satellite imagery continues to show a generally
shallow cumulus field along a stationary boundary draped across
northern IA. Despite the meager appearance of the cumulus field, new
convection has been intensifying at the intersection of the boundary
and convective outflow from an upstream cluster of storms across
southeast SD. Although lift is locally augmented at this
intersection, objective analysis trends over the past hour suggest 
convergence may be gradually increasing along the stationary
boundary across northwest IA, and RAP forecast soundings hint that
low-level parcels are near their convective temperatures. This
suggests that an isolated thunderstorm or two could develop either
1) along the stationary boundary (likely prior to sunset and the
onset of boundary-layer stabilization) or 2) along the convective
outflow as it gradually pushes east through the evening hours.
Confidence in either solution is somewhat low, and storm chances
decrease with eastward extent due to weaker convergence/implied
ascent. Given moderate instability in place (upwards of 3000 J/kg
MLCAPE), any storms that do form may initially be capable of
producing severe hail, though the lack of sufficient deep-layer
shear will limit the duration of this threat. Given the lack of
confidence in storm coverage and low potential for robust storm
organization, a watch is not expected.

..Moore/Hart.. 07/05/2021

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

ATTN...WFO...DMX...FSD...OAX...

LAT...LON   43519755 43799713 43489638 43379539 43369469 43279407
            43099342 42579342 42389401 42569502 42639637 42699702
            42889763 43099788 43519755

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