Tornado Warnings in Illinois, 2009

By month

25 of 108 tornado warnings covering Illinois in 2009 had a tornado report inside them; 49 of 68 tornado reports fell inside a warning, on average 16 minutes after it went out.

Illinois, 2009

Each office's whole area, 2009

An office's figures cover every county it serves, including across state lines.

Verified by the Iowa Environmental Mesonet's Cow, which matches each storm-based warning with the local storm reports inside its polygon while it was in force, within 15 km of its edge: a tornado warning counts as verified on a tornado report, a severe thunderstorm warning on hail of 1 inch or more, a gust of 58 mph or more, or wind damage, a flash flood warning on a flash flood report. The false alarm ratio is the share of warnings with no such report; "inside a warning" is the probability of detection, the share of reports that fell inside one; lead time runs from the warning's issue to each report inside it, counting zero for a report that came first. A warning with no report is not proof nothing happened: reports come from spotters, the public and damage surveys, and are thin where few people live.

• Sangamon County9
• Logan County8
• Fayette County7
• Morgan County6
• Saint Clair County5
• Greene County5
• Perry County5
• DeWitt County5
• Marion County5
• Jackson County5
• Adams County5
• Randolph County4
• Macoupin County4
• McLean County4
• Wayne County4
• Moultrie County4
• Shelby County4
• Pike County4
• Brown County4
• Macon County4
• Vermilion County4
• Franklin County3
• Henderson County3
• Warren County3
• Cass County3
• Scott County3
• Menard County3
• Champaign County3
• McHenry County3
• Iroquois County3
• Bond County3
• Calhoun County2
• Jersey County2
• Washington County2
• Jefferson County2
• Tazewell County2
• Clay County2
• Lawrence County2
• Will County2
• Williamson County2

1. August 19, 200927tornado warnings
2. March 8, 200914tornado warnings
3. May 15, 200911tornado warnings
4. June 20, 20099tornado warnings
5. June 19, 20098tornado warnings
6. May 14, 20097tornado warnings
7. May 8, 20096tornado warnings
8. June 21, 20094tornado warnings
9. June 8, 20093tornado warnings
10. July 8, 20093tornado warnings
11. May 25, 20092tornado warnings
12. June 2, 20092tornado warnings

Alerts in force nowTornadoes on recordThe radar archive20082010

National Weather Service watches, warnings, advisories and statements from the Iowa Environmental Mesonet's VTEC archive, which reconstructs tornado, severe thunderstorm, flash flood and marine warnings back to 1986 from the NWS text archive. Storm Prediction Center watches and mesoscale discussions from SPC's archive through the Mesonet. County centers from the US Census Bureau. Warning verification from the Mesonet's Cow. Rebuilt daily.