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Severe Thunderstorm Safety
Severe thunderstorms pose a threat to life and property. They produce large destructive hail of 3/4 inch in diameter or larger, and/or damaging downburst winds of around 60 mph or greater. Flooding rains, frequent cloud-to-ground lightning, and tornadoes are also possible in severe thunderstorms.
Here are some critical definitions to keep in mind:
| SEVERE THUNDERSTORM WATCH |
Conditions are favorable for the development of severe thunderstorms in and close to the watch area. Watches cover large areas of one or more states. Watches are usually in effect for several hours, with 6 hours being the most common. |
| SEVERE THUNDERSTORM WARNING |
Issued when a thunderstorm is currently producing, or is expected to produce, hail 3/4 of an inch or larger in diameter, and/or winds which equal or exceed 58 mph. Severe thunderstorms can result in the loss of life and/or property. Information in this warning includes: where the storm is, what towns will be affected, and the primary threat associated with the storm. Severe thunderstorm warnings are issued for individual counties or portions of counties, and are generally in effect for around an hour. |
Damaging "straight-line" or downburst winds from a thunderstorm can do as much damage as a weak to moderate tornado, so take severe thunderstorm warnings very seriously! Responding to a severe thunderstorm warning is what saved the lives of 150 people at the Parsons Manufacturing Company in Roanoke on July 13, 2004. The employees at Parsons implemented their severe weather safety plan, when a severe thunderstorm warning was issued nearly 15 minutes prior to the devastation caused by a violent F4 tornado.
Very large hail, golfball-size or larger, is not only destructive, but it occurs with the most violent of storms called supercells. Every year in the state of Illinois, supercells produce destructive hail ranging in size from baseballs to grapefruits.
