Severe Thunderstorms

In Chester County, we frequently experience thunderstorms throughout the spring, summer and even the fall. A thunderstorm, also known as an electrical storm, a lightning storm, or thundershower, is  a  type  of storm characterized by  the  presence  of lightning and  its acoustic effect  on the Earth’s   atmosphere known   as thunder. Thunderstorms   are   usually   accompanied by strong winds, heavy rain and sometimes snow, sleet, hail, or no precipitation at all.

Most flash flooding is caused by slow-moving thunderstorms in a local area or by heavy rains associated with hurricanes and tropical storms.

ReadyChesCo: Chester County's Notification System

The Chester County Department of Emergency Services has developed resources to
help residents prepare for thunderstorms, as well as other types of hazards. One tool
to help residents is, which allows residents to sign up to receive
emergency and non-emergency alerts for their community. By using this innovative
alert system, we are able to contact thousands of residents and visitors in seconds.

National Weather Service: Severe Thunderstorm Resources

Severe thunderstorms are officially defined as storms that are capable of producing hail that is an inch or larger or wind gusts over 58 mph. Hail this size can damage property such as plants, roofs and vehicles. Wind this strong is able to break off large branches, knock over trees or cause structural damage to trees. Some severe thunderstorms can produce hail larger than softballs or winds over 100 mph, so please pay attention to the weather so you know when severe storms are possible. Thunderstorms also produce tornadoes and dangerous lightning; heavy rain can cause flash flooding.

This National Weather Service website is designed to teach you how to stay safe in a severe thunderstorm. If you know what to do before, during, and after severe weather you can increase your chances of survival. You'll also find links to research, past events, other topics of interest, and downloadable materials about thunderstorms, lightning and tornadoes.