Alert archive / Illinois / Severe Thunderstorm Watches in 2021
Severe Thunderstorm Watch 435
The Storm Prediction Center issued this severe thunderstorm watch at Aug 12, 2021, 7:37 PM CDT for 16 counties in Illinois; 8 counties in Kentucky; 7 counties in Missouri. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 7:37 PM CDT (00:37 UTC)
- Expired
- Aug 12, 2021, 11:24 PM CDT
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1.5 in
- Strongest gust expected
- 55 kt
All 31 counties
Alexander County, IL, Franklin County, IL, Gallatin County, IL, Hamilton County, IL, Hardin County, IL, Jackson County, IL, Jefferson County, IL, Johnson County, IL, Massac County, IL, Perry County, IL, Pope County, IL, Pulaski County, IL, Saline County, IL, Union County, IL, White County, IL, Williamson County, IL, Ballard County, KY, Carlisle County, KY, Crittenden County, KY, Henderson County, KY, Livingston County, KY, McCracken County, KY, Union County, KY, Webster County, KY, Bollinger County, MO, Cape Girardeau County, MO, Mississippi County, MO, New Madrid County, MO, Perry County, MO, Scott County, MO, Stoddard County, MO
The radar
The Paducah radar (KPAH), 60 km from the middle of the area, began a volume at 00:37 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
- 5%
- One or more EF2 to EF5 tornadoes
- 2%
- Ten or more severe wind reports
- 20%
- One or more gusts of 65 knots or more
- 10%
- Ten or more severe hail reports
- 5%
- One or more hailstones of 2 inches or more
- 5%
- Six or more combined severe hail and wind reports
- 40%
Warnings issued inside it
2 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 8:07 PM CDT | Severe Thunderstorm Warning | PAH | Franklin, Jefferson, Perry | 38 min |
| Aug 12, 8:11 PM CDT | Severe Thunderstorm Warning | PAH | Jackson | 49 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
Nashville Metro, TN (KBNA), launched 00:00Z, 0.6 hours before the alert went out and 277 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
- 1786 J/kg
- Mixed-layer CIN
- -31 J/kg
- Mixed-layer LCL
- 1455 m above ground
- 0-6 km bulk shear
- 7 kt
- 0-1 km storm-relative helicity
- -25 m²/s²
- 0-3 km storm-relative helicity
- 0 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
137 WWUS20 KWNS 130032 SEL5 SPC WW 130032 ILZ000-INZ000-KYZ000-MOZ000-130600- URGENT - IMMEDIATE BROADCAST REQUESTED Severe Thunderstorm Watch Number 435 NWS Storm Prediction Center Norman OK 735 PM CDT Thu Aug 12 2021 The NWS Storm Prediction Center has issued a * Severe Thunderstorm Watch for portions of southern Illinois far southestern Indiana parts of western Kentucky southeastern Missouri * Effective this Thursday night and Friday morning from 735 PM until 100 AM CDT. * Primary threats include... Isolated damaging wind gusts to 65 mph possible SUMMARY...A fast-moving band of thunderstorms will continue shifting southeastward across the Mid-Mississippi Valley region this evening, accompanied by risk for locally damaging wind gusts. The severe thunderstorm watch area is approximately along and 35 statute miles either side of a line from 25 miles south southwest of Cape Girardeau MO to 35 miles east southeast of Mount Vernon IL. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU5). 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 433...WW 434... AVIATION...A few severe thunderstorms with hail surface and aloft to 1.5 inches. Extreme turbulence and surface wind gusts to 55 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 29040. ...Goss
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 12, 7:20 PM CDT | Mesoscale Discussion | SPC | Alexander, Franklin, Gallatin, Hamilton, Hardin, Jackson and 11 more | 85 min |
| Aug 12, 9:55 PM CDT | Mesoscale Discussion | SPC | Alexander, Franklin, Gallatin, Hamilton, Hardin, Johnson and 7 more | 95 min |
| Aug 13, 12:13 PM CDT | Mesoscale Discussion | SPC | Anderson, Bath, Boone, Bourbon, Boyd, Boyle and 55 more | 2 hr |
| Aug 12, 10:20 PM CDT | Mesoscale Discussion | SPC | Andrew, Atchison, Bates, Buchanan, Caldwell, Carroll and 18 more | 2 hr |
Nearby
Severe Thunderstorm Watches in Illinois, 2021Severe Thunderstorm Watches in Kentucky, 2021Severe Thunderstorm Watches in Missouri, 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.