Alert archive / Illinois / Mesoscale Discussions in 2021
Mesoscale Discussion 1494
The Storm Prediction Center issued this mesoscale discussion at Aug 11, 2021, 11:06 PM CDT for 4 states. It was in force for 84 min.
The area
The outline as issued.
The facts
- Issued
- Aug 11, 2021, 11:06 PM CDT (04:06 UTC)
- Expired
- Aug 12, 2021, 12:30 AM CDT
- In force
- 84 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 430
All 46 counties
Boone County, IL, Bureau County, IL, Carroll County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Grundy County, IL, Henry County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, Marshall County, IL, McHenry County, IL, Ogle County, IL, Putnam County, IL, Stark County, IL, Whiteside County, IL, Will County, IL, Elkhart County, IN, Kosciusko County, IN, LaGrange County, IN, Lake County, IN, LaPorte County, IN, Marshall County, IN, Noble County, IN, Porter County, IN, Saint Joseph County, IN, Starke County, IN, Steuben County, IN, Allegan County, MI, Barry County, MI, Berrien County, MI, Branch County, MI, Calhoun County, MI, Cass County, MI, Eaton County, MI, Hillsdale County, MI, Ingham County, MI, Jackson County, MI, Kalamazoo County, MI, Saint Joseph County, MI, Van Buren County, MI, Kenosha County, WI
The radar
The Chicago radar (KLOT), 62 km from the middle of the area, began a volume at 04:06 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
Lincoln, IL (KILX), launched 00:00Z, 4.1 hours before the alert went out and 213 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
- 3800 J/kg
- Mixed-layer CIN
- -58 J/kg
- Mixed-layer LCL
- 1058 m above ground
- 0-6 km bulk shear
- 19 kt
- 0-1 km storm-relative helicity
- 255 m²/s²
- 0-3 km storm-relative helicity
- 406 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 20.7
The text
As transmitted.
664
ACUS11 KWNS 120407
SWOMCD
SPC MCD 120406
MIZ000-OHZ000-INZ000-ILZ000-WIZ000-IAZ000-120530-
Mesoscale Discussion 1494
NWS Storm Prediction Center Norman OK
1106 PM CDT Wed Aug 11 2021
Areas affected...Northern IL...Northern IN...Southern Lower MI
Concerning...Severe Thunderstorm Watch 430...
Valid 120406Z - 120530Z
The severe weather threat for Severe Thunderstorm Watch 430
continues.
SUMMARY...Additional thunderstorm development is possible overnight,
but the magnitude and coverage of any severe risk remain quite
uncertain.
DISCUSSION...Thunderstorms which briefly intensified earlier across
northern IL and produced a near-severe gust west of Chicago have
recently dissipated, while other generally disorganized convection
continues across southwest lower MI in the wake of an earlier
thunderstorm cluster. The greatest thunderstorm coverage across WW
430 in the short term may continue to be across southwest MI, with
the primary low-level jet expected to remain focused in this area.
Further west, midlevel cumulus continues to be noted in IR imagery
across northwest IL, and additional storm development remains
possible into northern IL late tonight as a cold front moves into
the region.
While buoyancy remains rather large across the region, any
additional development later tonight will likely become increasingly
elevated with time as MLCINH increases, and effective shear for
elevated parcels will likely remain rather weak due to marginal (at
best) midlevel flow. Thus, any severe risk may remain isolated at
best, and it is possible that portions of WW 430 will be cancelled
early if no substantial redevelopment occurs by 05Z or sooner.
..Dean.. 08/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...IWX...GRR...LOT...ILX...MKX...DVN...
LAT...LON 42158977 42648809 42898562 42838488 42608429 42198436
41638469 41308540 41158661 40988845 40978913 41048961
41219035 41979015 42158977SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 11, 7:35 PM CDT | Mesoscale Discussion | SPC | Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 20 more | 85 min |
| Aug 11, 8:22 PM CDT | Severe Thunderstorm Watch | SPC | Bureau, Cook, DeKalb, DuPage, Ford, Grundy and 11 more | 8 hr |
| Aug 12, 3:16 AM CDT | Mesoscale Discussion | SPC | Bureau, Ford, Fulton, Grundy, Iroquois, Kankakee and 16 more | 119 min |
| Aug 12, 2:22 PM CDT | Mesoscale Discussion | SPC | Bond, Cass, Champaign, Christian, Clark, Clay and 26 more | 83 min |
| Aug 12, 5:19 PM CDT | Severe Thunderstorm Watch | SPC | Calhoun, Clinton, Greene, Jersey, Macoupin, Madison and 7 more | 5 hr |
| Aug 12, 6:06 PM CDT | Mesoscale Discussion | SPC | Calhoun, Jersey, Madison, Monroe, Saint Clair | 84 min |
| Aug 11, 9:17 PM CDT | Mesoscale Discussion | SPC | Genesee, Lapeer, Livingston, Macomb, Oakland, Saint Clair and 3 more | 88 min |
| Aug 12, 5:38 AM CDT | Mesoscale Discussion | SPC | Hillsdale, Jackson, Lenawee, Monroe, Oakland, Washtenaw and 1 more | 97 min |
Nearby
Mesoscale Discussions in Illinois, 2021Mesoscale Discussions in Michigan, 2021Mesoscale Discussions in Indiana, 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.