Alert archive / Illinois / Cook County / Severe Thunderstorm Warnings
Severe Thunderstorm Warnings in Cook County, Illinois, 2015
30 severe thunderstorm warnings in 2015. An alert counts here when it covered this county. The archive of severe thunderstorm warnings reaches back to 1986.
Cook County and its neighbors
Each county as a circle sized by its count in 2015. Tap one for its archive.
- Severe Thunderstorm Warnings
- 30
- Busiest month
- August11 severe thunderstorm warnings
- Busiest day
- August 3, 20157 severe thunderstorm warnings
Over time
By month
Warning verification
How often warnings here had a storm report inside them, and how much warning the reports had.
20 of 30 severe thunderstorm warnings covering Cook County in 2015 had a qualifying storm report inside them; 26 of 34 hail, wind and damage reports fell inside a warning, on average 27 minutes after it went out.
Cook County, 2015
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| Severe thunderstorm warnings | 30 | 20 | 33% | 34 | 76% | 27 min |
Each office's whole area, 2015
| Warnings | With a report | False alarm ratio | Reports | Inside a warning | Mean lead time | |
|---|---|---|---|---|---|---|
| NWS Chicago, IL: severe thunderstorm warnings | 147 | 73 | 50% | 252 | 71% | 20 min |
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.
The alerts
Every alert, in the order issued. Times are local, Central Time. Each opens its own page with the text, the map, the radar and the sounding.
| Issued | Product | Office | Lasted |
|---|---|---|---|
| Apr 9, 12:17 AM CDT | Severe Thunderstorm Warning | LOT | 43 min |
| Apr 9, 12:40 AM CDT | Severe Thunderstorm Warning | LOT | 24 min |
| Apr 9, 8:58 PM CDT | Severe Thunderstorm Warning | LOT | 32 min |
| Apr 9, 9:08 PM CDT | Severe Thunderstorm Warning | LOT | 37 min |
| Apr 9, 9:25 PM CDT | Severe Thunderstorm Warning | LOT | 35 min |
| Jun 8, 3:16 PM CDT | Severe Thunderstorm Warning | LOT | 44 min |
| Jun 8, 4:00 PM CDT | Severe Thunderstorm Warning | LOT | 30 min |
| Jun 10, 6:21 PM CDT | Severe Thunderstorm Warning | LOT | 39 min |
| Jun 22, 9:38 PM CDT | Severe Thunderstorm Warning | LOT | 37 min |
| Jul 13, 5:41 AM CDT | Severe Thunderstorm Warning | LOT | 64 min |
| Jul 13, 6:22 AM CDT | Severe Thunderstorm Warning | LOT | 53 min |
| Jul 13, 7:21 PM CDT | Severe Thunderstorm Warning | LOT | 24 min |
| Jul 13, 8:46 PM CDT | Severe Thunderstorm Warning | LOT | 29 min |
| Jul 13, 8:59 PM CDT | Severe Thunderstorm Warning | LOT | 31 min |
| Jul 13, 9:56 PM CDT | Severe Thunderstorm Warning | LOT | 33 min |
| Jul 17, 5:20 PM CDT | Severe Thunderstorm Warning | LOT | 40 min |
| Jul 18, 3:19 PM CDT | Severe Thunderstorm Warning | LOT | 26 min |
| Jul 18, 3:47 PM CDT | Severe Thunderstorm Warning | LOT | 13 min |
| Aug 2, 2:21 PM CDT | Severe Thunderstorm Warning | LOT | 39 min |
| Aug 2, 2:35 PM CDT | Severe Thunderstorm Warning | LOT | 25 min |
| Aug 2, 2:58 PM CDT | Severe Thunderstorm Warning | LOT | 17 min |
| Aug 2, 9:42 PM CDT | Severe Thunderstorm Warning | LOT | 63 min |
| Aug 2, 10:15 PM CDT | Severe Thunderstorm Warning | LOT | 45 min |
| Aug 2, 10:28 PM CDT | Severe Thunderstorm Warning | LOT | 32 min |
| Aug 2, 10:44 PM CDT | Severe Thunderstorm Warning | LOT | 31 min |
| Aug 2, 10:54 PM CDT | Severe Thunderstorm Warning | LOT | 66 min |
| Aug 2, 11:00 PM CDT | Severe Thunderstorm Warning | LOT | 9 min |
| Aug 2, 11:22 PM CDT | Severe Thunderstorm Warning | LOT | 53 min |
| Aug 18, 8:20 PM CDT | Severe Thunderstorm Warning | LOT | 25 min |
| Sep 18, 11:54 PM CDT | Severe Thunderstorm Warning | LOT | 66 min |
The busiest days
Days with the most alerts issued, by UTC date.
Nearby
Alerts in force nowTornadoes on recordForecastThe radar archive20142016
Sources
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.