Mesoscale Discussion 1171

Issued

Jul 6, 2021, 8:00 PM CDT (01:00 UTC)

Expired

Jul 6, 2021, 10:00 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe thunderstorm watch 338

The La Crosse radar (KARX), 60 km from the middle of the area, began a volume at 00:59 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.

467 
ACUS11 KWNS 070101
SWOMCD
SPC MCD 070100 
WIZ000-IAZ000-MNZ000-070300-

Mesoscale Discussion 1171
NWS Storm Prediction Center Norman OK
0800 PM CDT Tue Jul 06 2021

Areas affected...Southeast Minnesota...northeast Iowa and central
Wisconsin

Concerning...Severe Thunderstorm Watch 338...

Valid 070100Z - 070300Z

The severe weather threat for Severe Thunderstorm Watch 338
continues.

SUMMARY...An isolated severe wind threat may persist through roughly
10 PM CDT, but a gradual weakening trend will continue through the
evening hours.

DISCUSSION...Small convective clusters continue to propagate
eastward along the surface stationary front within WW 338. Although
a few outflow surges have moved off to the south of the front, weak
forcing for ascent has resulted in only isolated, and generally
transient, cells. Diabatic cooling due to training precipitation
along the front has begun to degrade mixed-layer instability and
reduce low-level lapse rates, suggesting a gradual decline in the
overall severe threat. Despite these trends, a few wind damage
reports and near-severe wind gusts have been noted in the past hour,
and regional VWPs still show 30-40 knots of 0-6/7 km bulk shear over
the region. Although instability has begun to wane, it should
remains sufficient for sustained convection in the near term -
particularly along the southern periphery of ongoing storms where
higher theta-e air continues to flow north near the surface. The
onset of diurnal cooling over the next 1-2 hours will continue the
gradual weakening trend, but an isolated severe/damaging wind gust
will remain possible in the near term given the residual CAPE/shear
parameters.

..Moore.. 07/07/2021

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

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

LAT...LON   43259411 43989354 44379171 44599007 44538874 44558774
            44308749 43798746 43438765 43478831 43498939 43399068
            43229223 43079352 43259411

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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.