Alert archive / Iowa / Mesoscale Discussions in 2021

Mesoscale Discussion 1370

July 28, 2021Jo Daviess County, Illinois; 8 counties in Iowa; 4 counties in Wisconsin

The Storm Prediction Center issued this mesoscale discussion at Jul 28, 2021, 12:50 AM CDT for Jo Daviess County, Illinois; 8 counties in Iowa; 4 counties in Wisconsin. It was in force for 55 min.

The area

The outline as issued.

The facts

Issued: Jul 28, 2021, 12:50 AM CDT (05:50 UTC)
Expired: Jul 28, 2021, 1:45 AM CDT
In force: 55 min
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 397

Counties Benton County, IA, Buchanan County, IA, Clayton County, IA, Delaware County, IA, Dubuque County, IA, Jackson County, IA, Jones County, IA, Linn County, IA, Jo Daviess County, IL, Grant County, WI, Iowa County, WI, Lafayette County, WI, Richland County, WI

The radar

The Quad Cities radar (KDVN), 114 km from the middle of the area, began a volume at 05:54 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.

The nearest sounding before it

Davenport, (KDVN), launched 00:00Z, 5.8 hours before the alert went out and 116 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 1554 J/kg
Mixed-layer CIN: -284 J/kg
Mixed-layer LCL: 1342 m above ground
0-6 km bulk shear: 40 kt
0-1 km storm-relative helicity: 68 m²/s²
0-3 km storm-relative helicity: 148 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

As transmitted.

336 
ACUS11 KWNS 280550
SWOMCD
SPC MCD 280550 
WIZ000-ILZ000-IAZ000-280645-

Mesoscale Discussion 1370
NWS Storm Prediction Center Norman OK
1250 AM CDT Wed Jul 28 2021

Areas affected...Portions of eastern IA...southwestern WI...and far
northwestern IL

Concerning...Severe Thunderstorm Watch 397...

Valid 280550Z - 280645Z

The severe weather threat for Severe Thunderstorm Watch 397
continues.

SUMMARY...An isolated hail/wind threat should diminish over the next
hour or so. Downstream watch issuance is not expected.

DISCUSSION...Ongoing strong convection across parts of eastern IA
and southwestern WI may continue to pose an isolated threat for
marginally severe hail and strong/gusty winds in the short term,
given the presence of around 1500-2500 J/kg of MLCAPE and 35-40 kt
of deep-layer shear. However, this activity will soon move
south-southeastward into an environment characterized by less
instability and increasing convective inhibition. The low-level
inflow into these storms is also rather weak and veered to
northwesterly. Accordingly, a gradual decrease in storm coverage and
intensity is forecast over the next couple of hours. Severe
Thunderstorm Watch 397 will likely be allowed to expire at 07Z as
scheduled, and a downstream watch is not expected.

..Gleason.. 07/28/2021

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

ATTN...WFO...MKX...DVN...ARX...DMX...

LAT...LON   42569216 42839188 43589009 43048963 42328967 41949070
            41899189 42179223 42569216

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 27, 7:33 PM CDT	Mesoscale Discussion	SPC	Allamakee, Black Hawk, Bremer, Buchanan, Butler, Cerro Gordo and 11 more	87 min
Jul 27, 8:03 PM CDT	Severe Thunderstorm Watch	SPC	Allamakee, Bremer, Buchanan, Chickasaw, Clayton, Delaware and 7 more	6 hr
Jul 27, 10:35 PM CDT	Mesoscale Discussion	SPC	Allamakee, Bremer, Buchanan, Chickasaw, Clayton, Delaware and 5 more	55 min
Jul 28, 5:09 PM CDT	Mesoscale Discussion	SPC	Barron, Bayfield, Burnett, Chippewa, Douglas, Dunn and 5 more	2 hr

Nearby

Mesoscale Discussions in Iowa, 2021 Mesoscale Discussions in Wisconsin, 2021 Mesoscale Discussions in Illinois, 2021 Every mesoscale discussion in 2021

Sources

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.