Alert archive / Wisconsin / Mesoscale Discussions in 2021

Mesoscale Discussion 1405

July 31, 20218 counties in Iowa; 7 counties in Minnesota; 39 counties in Wisconsin

The Storm Prediction Center issued this mesoscale discussion at Jul 31, 2021, 1:06 PM CDT for 8 counties in Iowa; 7 counties in Minnesota; 39 counties in Wisconsin. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Jul 31, 2021, 1:06 PM CDT (18:06 UTC)
Expired: Jul 31, 2021, 3:30 PM CDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

All 54 counties

Allamakee County, IA, Bremer County, IA, Chickasaw County, IA, Clayton County, IA, Fayette County, IA, Howard County, IA, Mitchell County, IA, Winneshiek County, IA, Dodge County, MN, Fillmore County, MN, Houston County, MN, Mower County, MN, Olmsted County, MN, Wabasha County, MN, Winona County, MN, Adams County, WI, Brown County, WI, Buffalo County, WI, Calumet County, WI, Chippewa County, WI, Clark County, WI, Columbia County, WI, Crawford County, WI, Dane County, WI, Dodge County, WI, Eau Claire County, WI, Fond du Lac County, WI, Grant County, WI, Green Lake County, WI, Iowa County, WI, Jackson County, WI, Jefferson County, WI, Juneau County, WI, La Crosse County, WI, Marathon County, WI, Marquette County, WI, Monroe County, WI, Outagamie County, WI, Ozaukee County, WI, Pepin County, WI, Portage County, WI, Richland County, WI, Sauk County, WI, Shawano County, WI, Sheboygan County, WI, Taylor County, WI, Trempealeau County, WI, Vernon County, WI, Washington County, WI, Waukesha County, WI, Waupaca County, WI, Waushara County, WI, Winnebago County, WI, Wood County, WI

The radar

The La Crosse radar (KARX), 103 km from the middle of the area, began a volume at 18:08 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

Green Bay/Straub, WI (KGRB), launched 12:00Z, 6.1 hours before the alert went out and 169 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: 14 J/kg
Mixed-layer CIN: -223 J/kg
Mixed-layer LCL: 922 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 100 m²/s²
0-3 km storm-relative helicity: 109 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

110 
ACUS11 KWNS 311806
SWOMCD
SPC MCD 311806 
WIZ000-IAZ000-MNZ000-312030-

Mesoscale Discussion 1405
NWS Storm Prediction Center Norman OK
0106 PM CDT Sat Jul 31 2021

Areas affected...Portions of central and southern Wisconsin into
extreme southeast Minnesota and far northeast Iowa

Concerning...Severe potential...Watch unlikely 

Valid 311806Z - 312030Z

Probability of Watch Issuance...20 percent

SUMMARY...Occasional bouts of damaging gusts and large hail may
occur with the stronger, longer-lasting storms. However, the overall
brevity and sparse coverage of the severe threat suggests that a WW
issuance is unlikely.

DISCUSSION...Semi-discrete multicellular clusters have been
gradually intensifying across portions of Wisconsin over the past
couple of hours, with more isolated convective development underway
to the WI/MN border (per latest MRMS mosaic radar data). These
storms are developing along/immediately ahead of a southward
propagating surface cold front. With surface temperatures warming
into the mid 70s F ahead of the front (shown by the latest METAR
observations), modest (i.e. 6-7 C/km) low-level lapse rates are
developing beneath -11 to -13C 500 mb temperatures, resulting in
500-1000 J/kg MLCAPE (per 17Z mesoanalysis). 40+ kts of 500 mb
northwesterly flow atop relatively weak westerly surface winds is
contributing to modest (i.e. 25 kts) effective bulk shear values. 

The current thermodynamic/kinematic environment supports continued
intensification of multicellular clusters through the afternoon
hours, with a couple of damaging gusts and perhaps some marginally
severe hail possible with the stronger, longer-lived updrafts.
However, given the skinny CAPE profiles amid mediocre deep-layer
shear, any severe threat that materialized is expected to be brief
and isolated. As such, a WW issuance is not currently anticipated.

..Squitieri/Grams.. 07/31/2021

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

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

LAT...LON   44069289 45299112 45399009 45148914 44778825 44488791
            43968766 43468765 43168770 42958786 42898803 42818888
            42748989 42639094 42619209 42779259 43529304 44069289

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jul 30, 8:16 PM CDT	Mesoscale Discussion	SPC	Adams, Cass, Fremont, Mills, Montgomery, Page and 2 more	59 min
Jul 30, 8:47 PM CDT	Severe Thunderstorm Watch	SPC	Adams, Decatur, Fremont, Mills, Montgomery, Page and 4 more	5 hr

Nearby

Mesoscale Discussions in Wisconsin, 2021 Mesoscale Discussions in Iowa, 2021 Mesoscale Discussions in Minnesota, 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.