Severe Thunderstorm

Why Talk About Severe Thunderstorms?

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(PDF File of  this Page) Despite their small size, all thunderstorms are dangerous. Every thunderstorm produces lightning, which kills more people each year than tornadoes. Heavy rain from thunderstorms can lead to flash flooding. Strong winds, hail, and tornadoes are also dangers associated with some thunderstorms.

Thunderstorms affect relatively small areas when compared with hurricanes and winter storms. The typical thunderstorm is 15 miles in diameter and lasts an average of 20 to 30 minutes. Of the estimated 100,000 thunderstorms that occur each year in the United States, only about 10 percent are classified as severe.

What Are Severe Thunderstorms, and What Causes Them?

The National Weather Service (NWS)considers a thunderstorm severe if it produces hail at least three-quarters of an inch in diameter, has winds of 58 miles per hour or higher, or produces a tornado. When a severe thunderstorm WARNING is issued, review what actions to take under a tornado warning or a flash flood warning.

Thunderstorms may occur singly, in clusters, or in lines. Some of the most severe weather occurs when a single thunderstorm affects one location for an extended time. Lightning is a major threat during a thunderstorm. It is the lightning that produces thunder in a thunderstorm. Lightning is very unpredictable, which increases the risk to individuals and property. In the United States, 75 to 100 people are killed each year by lightning, although most lightning victims do survive. Persons struck by lightning often report a variety of long-term, debilitating symptoms, including memory loss, attention deficits, sleep disorders, numbness, dizziness, stiffness in joints, irritability, fatigue, weakness, muscle spasms, depression, and an inability to sit for long. It is a myth that lightning never strikes the same place twice. In fact, lightning will strike several times in the same place in the course of one discharge.

Learn more about severe thunderstorm risk in your area. Contact your local emergency management office, National Weather Service (NWS) office, or American Red Cross chapter.

Awareness Information

A National Weather Service WATCH is a message indicating that conditions favor the occurrence of a certain type of hazardous weather. For example, a severe thunderstorm watch means that a severe thunderstorm is expected in the next six hours or so within an area approximately 120 to 150 miles wide and 300 to 400 miles long (36,000 to 60,000 square miles). The NWS Storm Prediction Center issues such watches. Local NWS forecast offices issue other watches (flash flood, winter weather, etc.) 12 to 36 hours in advance of a possible hazardous- weather or flooding event. Each local forecast office usually covers a state or a portion of a state.

An NWS WARNING indicates that a hazardous event is occurring or is imminent in about 30 minutes to an hour. Local NWS forecast offices issue warnings on a county-by-county basis.

Plan for a Thunderstorm

Develop a Family Disaster Plan. Please see the "Family Disaster Plan"section for general family planning information. Severe thunderstorm specific planning should include the following:

What to Tell Children

The sound of thunder can be especially frightening for young children. Take the "scariness" away by teaching them what to expect during a thunderstorm and how to be safe.

Assemble a Disaster Supplies Kit

Please see the section "Disaster Supplies Kit" for general supplies kit information. Severe Thunderstorm - specific supplies should include the Disaster Suplies Kit basics.

How to Protect Your Property

Media and Community Education Ideas

What to Do Before a Thunderstorm

What to Do During a Severe Thunderstorm WATCH

If you perceive a severe thunderstorm approaching:

What to Do During a Severe Thunderstorm WARNING

Listen to a NOAA Weather Radio or a battery-powered radio or television for updated emergency information. If the power goes out, you still will have access to important information.

What to Do at Home During a Thunderstorm WARNING

What to Do if You Are Outside and a Severe Thunderstorm Is Approaching

What to Do While driving During a Thunderstorm and Heavy Rain

What to Do After a Thunderstorm

What to Do if Someone Is Struck by Lightning

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