Mesoscale Discussion 1168

Issued

Jul 6, 2021, 5:22 PM CDT (22:22 UTC)

Expired

Jul 6, 2021, 7:15 PM CDT

In force

113 min

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 338

The La Crosse radar (KARX), 104 km from the middle of the area, began a volume at 22:20 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.

671 
ACUS11 KWNS 062223
SWOMCD
SPC MCD 062222 
WIZ000-IAZ000-MNZ000-SDZ000-070015-

Mesoscale Discussion 1168
NWS Storm Prediction Center Norman OK
0522 PM CDT Tue Jul 06 2021

Areas affected...Northern Iowa into southeast Minnesota and central
Wisconsin

Concerning...Severe Thunderstorm Watch 338...

Valid 062222Z - 070015Z

The severe weather threat for Severe Thunderstorm Watch 338
continues.

SUMMARY...Isolated severe wind, and perhaps a few instances of hail,
remain possible across WW 338 for the next couple of hours.

DISCUSSION...Storms that have developed along the surface front over
the past 2 hours have evolved from semi-discrete storms to mainly
convective clusters - largely due to mean flow oriented along the
initiating boundary. This has limited the potential for robust,
long-lived cell organization over the past hour, and the severe hail
threat has correspondingly diminished. However, damaging winds as
well as measured 60+ mph winds have been recently reported,
indicating that severe winds remain a concern. Overall, the
environment along and south of the broken line of storms across
southern portions of WW 338 remains favorable for strong downdrafts
with 1000-2000 J/kg MLCAPE overlapping an area with 7-8 C/km
low-level lapse rates. The greatest severe wind risk will likely
reside across central WI where the best instability/low-level lapse
rates are co-located and nearby clusters have displayed periods of
organized linear structure. Convection may gradually spread
southward into this environment along outflows and/or the sagging
surface front, but the southern extent of storm coverage is somewhat
uncertain given the mean zonal flow. Additionally, convection moving
eastward across Lake Michigan may reach the western shores of lower
MI within the next hour. Supportive instability across lower MI may
allow for some storm intensification, but weaker deep-layer shear
should limit the overall severe threat.

..Moore.. 07/06/2021

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

ATTN...WFO...GRB...MKX...ARX...MPX...DMX...FSD...

LAT...LON   43469656 43959547 44089354 44369162 44529000 44498910
            44158802 43698774 43198776 42728840 42989002 43079148
            42949351 42829477 42759561 42649605 42929654 43469656

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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.