Alert archive / Illinois / Severe Thunderstorm Watches in 2012

Severe Thunderstorm Watch 258

May 6, 201241 counties in Illinois; 5 counties in Iowa; 31 counties in Missouri

The Storm Prediction Center issued this severe thunderstorm watch at May 6, 2012, 1:42 PM CDT for 41 counties in Illinois; 5 counties in Iowa; 31 counties in Missouri. It was in force for 7 hr.

The area

The outline as issued.

The facts

Issued: May 6, 2012, 1:42 PM CDT (18:42 UTC)
Expired: May 6, 2012, 9:00 PM CDT
In force: 7 hr
Issued by: the Storm Prediction Center
Largest hail expected: 2 in
Strongest gust expected: 60 kt

All 77 counties

Des Moines County, IA, Henry County, IA, Lee County, IA, Louisa County, IA, Van Buren County, IA, Adams County, IL, Brown County, IL, Bureau County, IL, Cass County, IL, Champaign County, IL, Cook County, IL, DeWitt County, IL, Ford County, IL, Fulton County, IL, Grundy County, IL, Hancock County, IL, Henderson County, IL, Henry County, IL, Iroquois County, IL, Kankakee County, IL, Kendall County, IL, Knox County, IL, LaSalle County, IL, Livingston County, IL, Logan County, IL, Macon County, IL, Marshall County, IL, Mason County, IL, McDonough County, IL, McLean County, IL, Menard County, IL, Mercer County, IL, Morgan County, IL, Peoria County, IL, Piatt County, IL, Pike County, IL, Putnam County, IL, Sangamon County, IL, Schuyler County, IL, Scott County, IL, Stark County, IL, Tazewell County, IL, Vermilion County, IL, Warren County, IL, Will County, IL, Woodford County, IL, Adair County, MO, Audrain County, MO, Boone County, MO, Caldwell County, MO, Carroll County, MO, Chariton County, MO, Clark County, MO, Cooper County, MO, Daviess County, MO, Grundy County, MO, Henry County, MO, Howard County, MO, Johnson County, MO, Knox County, MO, Lafayette County, MO, Lewis County, MO, Linn County, MO, Livingston County, MO, Macon County, MO, Marion County, MO, Moniteau County, MO, Monroe County, MO, Pettis County, MO, Pike County, MO, Ralls County, MO, Randolph County, MO, Ray County, MO, Saline County, MO, Scotland County, MO, Shelby County, MO, Sullivan County, MO

The radar

The St Louis radar (KLSX), 170 km from the middle of the area, began a volume at 18:43 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: 20%
One or more EF2 to EF5 tornadoes: 5%
Ten or more severe wind reports: 40%
One or more gusts of 65 knots or more: 30%
Ten or more severe hail reports: 60%
One or more hailstones of 2 inches or more: 50%
Six or more combined severe hail and wind reports: 80%

Warnings issued inside it

41 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
May 6, 1:42 PM CDT	Severe Thunderstorm Warning	DVN	Bureau, Henry	63 min
May 6, 1:47 PM CDT	Severe Thunderstorm Warning	EAX	Chariton, Randolph	28 min
May 6, 1:56 PM CDT	Severe Thunderstorm Warning	LOT	Ford, Iroquois, Kankakee, Livingston	64 min
May 6, 1:57 PM CDT	Severe Thunderstorm Warning	EAX	Howard, Saline	33 min
May 6, 2:04 PM CDT	Tornado Warning	DVN	Bureau	26 min
May 6, 2:06 PM CDT	Severe Thunderstorm Warning	ILX	Knox, Peoria, Stark	54 min
May 6, 2:15 PM CDT	Severe Thunderstorm Warning	EAX	Randolph	30 min
May 6, 2:31 PM CDT	Severe Thunderstorm Warning	DVN	Bureau, Putnam	44 min
May 6, 2:36 PM CDT	Tornado Warning	ILX	Marshall, Stark	39 min
May 6, 2:37 PM CDT	Severe Thunderstorm Warning	LOT	Cook	38 min
May 6, 2:37 PM CDT	Severe Thunderstorm Warning	LSX	Monroe, Shelby	53 min
May 6, 2:57 PM CDT	Severe Thunderstorm Warning	LOT	Ford, Iroquois, Kankakee	63 min
May 6, 3:05 PM CDT	Severe Thunderstorm Warning	LSX	Monroe	40 min
May 6, 3:07 PM CDT	Tornado Warning	ILX	Marshall	53 min
May 6, 3:14 PM CDT	Severe Thunderstorm Warning	DVN	Bureau, Putnam	36 min
May 6, 3:19 PM CDT	Flash Flood Warning	LOT	Ford, Grundy, Iroquois, Kankakee, Livingston	6 hr
May 6, 3:26 PM CDT	Tornado Warning	LOT	Iroquois	64 min
May 6, 3:31 PM CDT	Severe Thunderstorm Warning	LOT	Grundy, LaSalle, Livingston	59 min
May 6, 3:35 PM CDT	Severe Thunderstorm Warning	LSX	Marion, Ralls	25 min
May 6, 3:39 PM CDT	Flash Flood Warning	LOT	Grundy, LaSalle, Livingston	6 hr
May 6, 3:41 PM CDT	Severe Thunderstorm Warning	LOT	Iroquois	64 min
May 6, 3:42 PM CDT	Tornado Warning	LOT	LaSalle, Livingston	48 min
May 6, 3:43 PM CDT	Severe Thunderstorm Warning	LOT	LaSalle, Livingston	52 min
May 6, 4:02 PM CDT	Severe Thunderstorm Warning	LOT	Ford, Iroquois, Livingston	48 min
May 6, 4:03 PM CDT	Severe Thunderstorm Warning	ILX	Champaign, Vermilion	57 min
May 6, 4:03 PM CDT	Severe Thunderstorm Warning	LOT	Ford, Grundy, Kankakee, Livingston	57 min
May 6, 4:13 PM CDT	Severe Thunderstorm Warning	LSX	Pike, Ralls	32 min
May 6, 4:28 PM CDT	Severe Thunderstorm Warning	LOT	Grundy, LaSalle, Livingston	32 min
May 6, 4:37 PM CDT	Severe Thunderstorm Warning	LSX	Pike	23 min
May 6, 4:46 PM CDT	Tornado Warning	LOT	Iroquois	44 min
May 6, 4:56 PM CDT	Severe Thunderstorm Warning	LOT	Iroquois	64 min
May 6, 5:00 PM CDT	Severe Thunderstorm Warning	ILX	Vermilion	45 min
May 6, 5:01 PM CDT	Severe Thunderstorm Warning	LOT	Ford, Iroquois, Livingston	59 min
May 6, 5:15 PM CDT	Flash Flood Warning	LOT	Ford, Iroquois	6 hr
May 6, 5:21 PM CDT	Tornado Warning	ILX	Vermilion	39 min
May 6, 5:25 PM CDT	Tornado Warning	LOT	Ford, Iroquois	50 min
May 6, 6:02 PM CDT	Severe Thunderstorm Warning	EAX	Cass, Jackson, Johnson	28 min
May 6, 6:09 PM CDT	Flash Flood Warning	ILX	Vermilion	6 hr
May 6, 6:15 PM CDT	Severe Thunderstorm Warning	EAX	Bates, Cass, Henry, Johnson	30 min
May 6, 6:47 PM CDT	Severe Thunderstorm Warning	EAX	Johnson, Lafayette	28 min
May 6, 6:58 PM CDT	Severe Thunderstorm Warning	EAX	Johnson	32 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

Davenport, (KDVN), launched 12:00Z, 6.7 hours before the alert went out and 191 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.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 2361 J/kg
Mixed-layer CIN: -82 J/kg
Mixed-layer LCL: 571 m above ground
0-6 km bulk shear: 31 kt
0-1 km storm-relative helicity: 181 m²/s²
0-3 km storm-relative helicity: 188 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 9.6

Open this sounding in Storm Lab

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 6, 8:40 AM CDT	Mesoscale Discussion	SPC	Bureau, Fulton, Hancock, Henderson, Henry, Knox and 12 more	65 min
May 6, 9:29 AM CDT	Severe Thunderstorm Watch	SPC	Bureau, Carroll, Fulton, Hancock, Henderson, Henry and 11 more	4 hr
May 6, 1:22 PM CDT	Mesoscale Discussion	SPC	Adams, Brown, Cass, Fulton, Grundy, Hancock and 20 more	53 min
May 6, 3:56 PM CDT	Mesoscale Discussion	SPC	Adams, Brown, Cass, Champaign, DeWitt, Ford and 32 more	64 min
May 6, 5:07 PM CDT	Mesoscale Discussion	SPC	Clark, Edgar, Iroquois, Vermilion	53 min
May 5, 10:03 PM CDT	Severe Thunderstorm Watch	SPC	Buena Vista, Cherokee, Clay, Dickinson, Ida, Lyon and 6 more	7 hr
May 5, 11:31 PM CDT	Mesoscale Discussion	SPC	Lyon	89 min
May 6, 2:12 AM CDT	Mesoscale Discussion	SPC	Buena Vista, Butler, Cerro Gordo, Cherokee, Clay, Dickinson and 17 more	63 min
May 6, 4:55 AM CDT	Mesoscale Discussion	SPC	Adair, Adams, Audubon, Cass, Fremont, Guthrie and 8 more	2 hr
May 6, 7:17 AM CDT	Severe Thunderstorm Watch	SPC	Adair, Adams, Appanoose, Clarke, Dallas, Davis and 16 more	6 hr
May 6, 2:40 PM CDT	Mesoscale Discussion	SPC	Platte	95 min
May 6, 3:49 PM CDT	Severe Thunderstorm Watch	SPC	Andrew, Bates, Buchanan, Cass, Clay, Clinton and 10 more	7 hr

Nearby

Severe Thunderstorm Watches in Illinois, 2012 Severe Thunderstorm Watches in Missouri, 2012 Severe Thunderstorm Watches in Iowa, 2012 Every severe thunderstorm watch in 2012

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.