HOME FORECAST PAST WEATHER SAFETY INFORMATION EDUCATION NEWS SEARCH ABOUT Safety National Program Severe Thunderstorm Safety Weather.gov > Safety > Severe Thunderstorm Safety Severe Thunderstorms Watch vs. Warning Prepare for Severe Thunderstorms During Severe Thunderstorms After Severe Thunderstorms Severe Thunderstorm Resources Severe Weather OutlookStormReady!Severe Thunderstorm ArchiveLightning SafetyFlood SafetyOutreach and EducationLinks and Partners 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. These hazards are covered in more detail under the tornado, lightning safety and flood safety websites. This 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. If you, or someone you know, have been a victim of severe weather, please share your story so we can prevent others from becoming victims. When you write, please note that NWS has permission to use your story and, if possible, let us know the town and state you were in and the year the event took place. US Dept of Commerce National Oceanic and Atmospheric Administration National Weather Service Safety 1325 East West Highway Silver Spring, MD 20910 Comments? Questions? Please Contact Us. Disclaimer Information Quality Help Glossary Privacy Policy Freedom of Information Act (FOIA) About Us Career Opportunities