Alert archive / Iowa / Mesoscale Discussions in 2021
Mesoscale Discussion 1489
The Storm Prediction Center issued this mesoscale discussion at Aug 11, 2021, 5:40 PM CDT for Carroll County, Jo Daviess County, Stephenson County, Illinois; 11 counties in Iowa; 9 counties in Wisconsin. It was in force for 95 min.
The area
The outline as issued.
The facts
- Issued
- Aug 11, 2021, 5:40 PM CDT (22:40 UTC)
- Expired
- Aug 11, 2021, 7:15 PM CDT
- In force
- 95 min
- Issued by
- the Storm Prediction Center
- Concerning
- Tornado watch 424
All 23 counties
Benton County, IA, Cedar County, IA, Clinton County, IA, Delaware County, IA, Dubuque County, IA, Iowa County, IA, Jackson County, IA, Johnson County, IA, Jones County, IA, Linn County, IA, Poweshiek County, IA, Carroll County, IL, Jo Daviess County, IL, Stephenson County, IL, Columbia County, WI, Dane County, WI, Grant County, WI, Green County, WI, Iowa County, WI, Jefferson County, WI, Lafayette County, WI, Rock County, WI, Sauk County, WI
The radar
The Quad Cities radar (KDVN), 71 km from the middle of the area, began a volume at 22:40 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Davenport, (KDVN), launched 12:00Z, 10.7 hours before the alert went out and 72 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
- 2852 J/kg
- Mixed-layer CIN
- -107 J/kg
- Mixed-layer LCL
- 1040 m above ground
- 0-6 km bulk shear
- 34 kt
- 0-1 km storm-relative helicity
- 170 m²/s²
- 0-3 km storm-relative helicity
- 193 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 3.7
The text
As transmitted.
742
ACUS11 KWNS 112241
SWOMCD
SPC MCD 112240
WIZ000-ILZ000-IAZ000-120015-
Mesoscale Discussion 1489
NWS Storm Prediction Center Norman OK
0540 PM CDT Wed Aug 11 2021
Areas affected...Eastern IA...Southern WI...Northwest IL
Concerning...Tornado Watch 424...
Valid 112240Z - 120015Z
The severe weather threat for Tornado Watch 424 continues.
SUMMARY...Ongoing storms from eastern IA into southwest WI will
continue to pose a short-term severe threat. The eastward extent of
the threat this evening remains uncertain due to the impact of
earlier convection across southern WI/northern IL. Storm coverage is
being monitored for possible watch issuance across eastern IA.
DISCUSSION...At 2230Z, a few intense cells are ongoing from eastern
IA into southwest WI, within an environment characterized by large
CAPE and effective shear of 25-35 kt. The mature storms in this
region will continue to pose a short-term threat of locally damaging
wind, hail, and perhaps a tornado or two into the early evening as
they move eastward.
Downstream into south-central WI/northern IL, the impact of morning
convection is still evident, with relatively strong MLCINH
persisting per recent mesoanalyses and low-level stratus increasing
in recent visible imagery. Ongoing storms may tend to struggle with
time as they move eastward, especially given the relatively limited
large-scale ascent as the primary vorticity maxima move
northeastward away from the area. Low-level warm advection may
promote an increase in storm coverage later this evening, though
this scenario remains somewhat uncertain.
Meanwhile, across eastern IA, storm coverage remains uncertain into
this evening, though with a conditionally favorable environment in
place, watch issuance remains possible to the southwest of WW 424 if
additional intense thunderstorm development appears imminent.
..Dean/Goss.. 08/11/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...MKX...DVN...ARX...DMX...
LAT...LON 41819038 41519153 41449218 41559250 41779269 41919247
42819117 43648959 43388865 42838860 42298937 41819038SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 10, 7:38 PM CDT | Severe Thunderstorm Watch | SPC | Kankakee | 5 hr |
| Aug 11, 1:20 AM CDT | Mesoscale Discussion | SPC | Bureau, Ford, Fulton, Grundy, Henry, Iroquois and 15 more | 115 min |
| Aug 11, 4:49 AM CDT | Mesoscale Discussion | SPC | Adams | 86 min |
| Aug 11, 6:26 AM CDT | Mesoscale Discussion | SPC | Adams, Brown, Cass, Fulton, Hancock, Henderson and 12 more | 2 hr |
| Aug 11, 8:34 AM CDT | Mesoscale Discussion | SPC | Bureau, Cook, DeKalb, DuPage, Ford, Grundy and 13 more | 86 min |
| Aug 11, 8:52 AM CDT | Severe Thunderstorm Watch | SPC | Cook, DeKalb, DuPage, Grundy, Kane, Kankakee and 6 more | 4 hr |
| Aug 11, 9:52 AM CDT | Mesoscale Discussion | SPC | Cook, DuPage, Grundy, Kane, Kankakee, Lake and 1 more | 83 min |
| Aug 11, 3:56 PM CDT | Mesoscale Discussion | SPC | Carroll, Hancock, Henderson, Henry, Jo Daviess, Mercer and 2 more | 3 hr |
| Aug 11, 11:48 AM CDT | Mesoscale Discussion | SPC | Allamakee | 117 min |
| Aug 11, 12:17 PM CDT | Tornado Watch | SPC | Allamakee, Clayton | 8 hr |
| Aug 10, 7:12 PM CDT | Mesoscale Discussion | SPC | Manitowoc, Racine, Sheboygan | 63 min |
| Aug 11, 7:27 AM CDT | Mesoscale Discussion | SPC | Barron, Buffalo, Burnett, Chippewa, Dunn, Eau Claire and 8 more | 2 hr |
| Aug 11, 2:02 PM CDT | Mesoscale Discussion | SPC | Adams, Brown, Calumet, Columbia, Crawford, Dodge and 20 more | 88 min |
| Aug 11, 6:45 PM CDT | Mesoscale Discussion | SPC | Milwaukee, Racine | 90 min |
Nearby
Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Wisconsin, 2021Mesoscale Discussions in Illinois, 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.