Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1384
The Storm Prediction Center issued this mesoscale discussion at Jul 29, 2021, 1:34 AM CDT for 9 counties in Illinois; 6 counties in Wisconsin. It was in force for 86 min.
The area
The outline as issued.
The facts
- Issued
- Jul 29, 2021, 1:34 AM CDT (06:34 UTC)
- Expired
- Jul 29, 2021, 3:00 AM CDT
- In force
- 86 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 399...400
Counties Boone County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Kane County, IL, Kendall County, IL, Lake County, IL, McHenry County, IL, Winnebago County, IL, Kenosha County, WI, Milwaukee County, WI, Racine County, WI, Rock County, WI, Walworth County, WI, Waukesha County, WI
The radar
The Milwaukee radar (KMKX), 64 km from the middle of the area, began a volume at 06:32 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, 6.6 hours before the alert went out and 201 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.
- Mixed-layer CAPE
- 4022 J/kg
- Mixed-layer CIN
- -33 J/kg
- Mixed-layer LCL
- 1022 m above ground
- 0-6 km bulk shear
- 28 kt
- 0-1 km storm-relative helicity
- 52 m²/s²
- 0-3 km storm-relative helicity
- 90 m²/s²
- Significant tornado parameter
- 1.0
- Supercell composite
- 6.8
The text
As transmitted.
846
ACUS11 KWNS 290634
SWOMCD
SPC MCD 290634
INZ000-ILZ000-WIZ000-290800-
Mesoscale Discussion 1384
NWS Storm Prediction Center Norman OK
0134 AM CDT Thu Jul 29 2021
Areas affected...Portions of southeastern WI and northeastern
IL...including Chicago
Concerning...Severe Thunderstorm Watch 399...400...
Valid 290634Z - 290800Z
The severe weather threat for Severe Thunderstorm Watch 399, 400
continues.
SUMMARY...The greatest threat for 60-75 mph wind gusts and perhaps a
tornado will likely focus across portions of southeastern Wisconsin
and northeastern Illinois in the short term.
DISCUSSION...Radar imagery from KMKX has recently shown a bookend
vortex with at least one prior CC minimum moving from Jefferson into
Waukesha counties in southeastern WI around 0615-0630Z. With ample
low-level shear still present ahead of the ongoing MCS across
southern WI and to the south of a warm front located over Lake
Michigan and Lower MI, a threat for a tornado or two embedded within
the MCS will likely persist in the short term. Otherwise, scattered
severe/damaging winds of 60-75 mph will impact a greater portion of
southeastern WI into northeastern IL, as 1500-2500 J/kg of MLCAPE
and a rich low-level airmass are present across this area. The apex
of the bow appears to be moving southward around 35-45 kt, and the
overall severe threat is expected to increase across northeastern
IL, including the Chicago metro, over the next couple of hours (by 3
AM CDT).
..Gleason.. 07/29/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...MKX...
LAT...LON 42808935 41968929 41568849 41568753 41848747 42308771
42728768 42958767 43178824 42948870 42808935SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 29, 12:32 AM CDT | Mesoscale Discussion | SPC | Boone, Carroll, Cook, DeKalb, DuPage, Grundy and 11 more | 88 min |
| Jul 29, 1:00 AM CDT | Severe Thunderstorm Watch | SPC | Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 18 more | 5 hr |
| Jul 29, 3:18 AM CDT | Mesoscale Discussion | SPC | Cook, DeKalb, DuPage, Grundy, Iroquois, Kankakee and 4 more | 87 min |
| Jul 29, 2:19 PM CDT | Mesoscale Discussion | SPC | Adams, Brown, Cass, Champaign, Christian, Clark and 34 more | 116 min |
| Jul 28, 7:17 PM CDT | Severe Thunderstorm Watch | SPC | Adams, Barron, Brown, Buffalo, Burnett, Calumet and 61 more | 7 hr |
| Jul 28, 8:59 PM CDT | Mesoscale Discussion | SPC | Chippewa, Clark, Eau Claire, Jackson, Monroe, Trempealeau | 61 min |
| Jul 28, 9:51 PM CDT | Mesoscale Discussion | SPC | Eau Claire, Jackson, Monroe | 54 min |
| Jul 28, 10:17 PM CDT | Mesoscale Discussion | SPC | Buffalo, Dunn, Pepin, Pierce, Saint Croix | 58 min |
| Jul 28, 11:24 PM CDT | Mesoscale Discussion | SPC | Adams, Buffalo, Calumet, Columbia, Crawford, Dane and 34 more | 96 min |
Nearby
Mesoscale Discussions in Illinois, 2021Mesoscale Discussions in Wisconsin, 2021Every 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.