Alert archive / Illinois / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 391
The Storm Prediction Center issued this severe thunderstorm watch at Jul 24, 2021, 3:32 PM CDT for 23 counties in Illinois; 21 counties in Indiana; 5 counties in Michigan. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Jul 24, 2021, 3:32 PM CDT (20:32 UTC)
- Expired
- Jul 24, 2021, 10:00 PM CDT
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 60 kt
All 49 counties
Bureau County, IL, Cook County, IL, DeKalb County, IL, DuPage County, IL, Ford County, IL, Grundy County, IL, Iroquois County, IL, Kane County, IL, Kankakee County, IL, Kendall County, IL, Lake County, IL, LaSalle County, IL, Lee County, IL, Livingston County, IL, Marshall County, IL, McHenry County, IL, McLean County, IL, Peoria County, IL, Putnam County, IL, Stark County, IL, Tazewell County, IL, Will County, IL, Woodford County, IL, Benton County, IN, Cass County, IN, Elkhart County, IN, Fulton County, IN, Jasper County, IN, Kosciusko County, IN, LaGrange County, IN, Lake County, IN, LaPorte County, IN, Marshall County, IN, Miami County, IN, Newton County, IN, Noble County, IN, Porter County, IN, Pulaski County, IN, Saint Joseph County, IN, Starke County, IN, Steuben County, IN, Wabash County, IN, White County, IN, Whitley County, IN, Berrien County, MI, Branch County, MI, Cass County, MI, Hillsdale County, MI, Saint Joseph County, MI
The radar
The Chicago radar (KLOT), 27 km from the middle of the area, began a volume at 20:31 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.
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 10%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 40%
- One or more gusts of 65 knots or more
- 20%
- Ten or more severe hail reports
- 20%
- One or more hailstones of 2 inches or more
- 10%
- Six or more combined severe hail and wind reports
- 60%
Warnings issued inside it
15 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 24, 3:54 PM CDT | Severe Thunderstorm Warning | LOT | Cook, DuPage | 51 min |
| Jul 24, 4:26 PM CDT | Severe Thunderstorm Warning | LOT | Cook | 49 min |
| Jul 24, 5:01 PM CDT | Severe Thunderstorm Warning | LOT | Cook | 59 min |
| Jul 24, 5:36 PM CDT | Severe Thunderstorm Warning | LOT | Will | 16 min |
| Jul 24, 5:49 PM CDT | Severe Thunderstorm Warning | IWX | LaPorte | 41 min |
| Jul 24, 6:00 PM CDT | Severe Thunderstorm Warning | LOT | Porter | 60 min |
| Jul 24, 6:07 PM CDT | Severe Thunderstorm Warning | LOT | Kankakee, Will | 53 min |
| Jul 24, 6:17 PM CDT | Severe Thunderstorm Warning | IWX | Elkhart, Saint Joseph | 43 min |
| Jul 24, 6:24 PM CDT | Severe Thunderstorm Warning | IWX | LaPorte, Marshall, Saint Joseph, Starke | 51 min |
| Jul 24, 6:36 PM CDT | Severe Thunderstorm Warning | LOT | Kankakee | 39 min |
| Jul 24, 6:48 PM CDT | Severe Thunderstorm Warning | IWX | Elkhart, Kosciusko, Marshall, Saint Joseph | 57 min |
| Jul 24, 6:49 PM CDT | Severe Thunderstorm Warning | IWX | Elkhart, Kosciusko, Marshall, Saint Joseph | 56 min |
| Jul 24, 7:22 PM CDT | Severe Thunderstorm Warning | LOT | Iroquois | 53 min |
| Jul 24, 8:10 PM CDT | Severe Thunderstorm Warning | LOT | Iroquois | 65 min |
| Jul 24, 8:51 PM CDT | Tornado Warning | LOT | Iroquois | 24 min |
Discussions around it
SPC mesoscale discussions over the same counties from four hours before the watch to its end.
The nearest sounding before it
Lincoln, IL (KILX), launched 12:00Z, 8.5 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.
- Mixed-layer CAPE
- 553 J/kg
- Mixed-layer CIN
- -31 J/kg
- Mixed-layer LCL
- 964 m above ground
- 0-6 km bulk shear
- 22 kt
- 0-1 km storm-relative helicity
- 47 m²/s²
- 0-3 km storm-relative helicity
- 65 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
084 WWUS20 KWNS 242029 SEL1 SPC WW 242029 ILZ000-INZ000-MIZ000-LMZ000-250300- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 391 NWS Storm Prediction Center Norman OK 330 PM CDT Sat Jul 24 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of Northern Illinois Northern Indiana Southwest Lower Michigan Lake Michigan * Effective this Saturday afternoon and evening from 330 PM until 1000 PM CDT. * Primary threats include... Scattered damaging wind gusts to 70 mph possible Isolated large hail events to 1.5 inches in diameter possible SUMMARY...Thunderstorms are slowly intensifying along a line from north of Chicago into northwest Illinois. These storms will spread southward through the afternoon, posing a risk of locally damaging wind gusts and hail. The severe thunderstorm watch area is approximately along and 45 statute miles north and south of a line from 50 miles west southwest of Marseilles IL to 35 miles southeast of Kalamazoo MI. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU1). PRECAUTIONARY/PREPAREDNESS ACTIONS... REMEMBER...A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings. Severe thunderstorms can and occasionally do produce tornadoes. && OTHER WATCH INFORMATION...CONTINUE...WW 390... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 30025. ...Hart
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Jul 24, 3:00 PM CDT | Mesoscale Discussion | SPC | Boone, Bureau, Carroll, Cook, DeKalb, DuPage and 17 more | 2 hr |
| Jul 24, 5:21 PM CDT | Mesoscale Discussion | SPC | Bureau, Cook, DuPage, Ford, Grundy, Iroquois and 12 more | 114 min |
| Jul 24, 1:21 PM CDT | Mesoscale Discussion | SPC | Elkhart, LaGrange, LaPorte, Marshall, Saint Joseph, Starke and 1 more | 114 min |
| Jul 24, 10:44 AM CDT | Mesoscale Discussion | SPC | Alcona, Alpena, Arenac, Bay, Clare, Crawford and 16 more | 3 hr |
| Jul 24, 2:16 PM CDT | Severe Thunderstorm Watch | SPC | Alcona, Allegan, Arenac, Barry, Bay, Calhoun and 40 more | 7 hr |
Nearby
Severe Thunderstorm Watches in Illinois, 2021Severe Thunderstorm Watches in Indiana, 2021Severe Thunderstorm Watches in Michigan, 2021Every severe thunderstorm watch 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.