The factors used by the National Weather Service to determine if a thunderstorm is severe are winds greater than 57 mph and hail greater than 3/4 inch in diameter or about the size of a penny. Typically, a severe thunderstorm lasts about 30 minutes and occurs in the afternoon and evening hours during the Spring and Summer months. However, severe weather is possible any time of the day and any time of the year. A special class of severe thunderstorms called "Supercells" are particularly violent and can last for several hours. Tornadoes are often produced from these supercell thunderstorms.
So what can you do to protect yourself and your family:
The best thing to do is to have a plan of action in place before threatening weather develops. Know what the difference between a watch and warning are. A Severe Thunderstorm Watch means conditions are favorable for severe thunderstorms to develop, but there is not an imminent threat. A Severe Thunderstorm Warning means a severe thunderstorm has been detected and an imminent threat to life and property has developed.
Know your area so you can track storms, listen to a weather radio, local TV or radio reports. Make sure you have battery backup. Monitor any forecasts if threatening weather is possible and you are planning outdoor activities.
If severe weather is imminent, and you are inside, move to shelter such as a basement or an interior room on the lowest floor of the building. Remember, it’s best to put as many walls between you and the outside as possible.
If you are caught outside, try to seek shelter in a sturdy structure.
For further information on severe thunderstorms please visit Storm Prediction Center