Although hurricanes are a significant source of wind damage, severe thunderstorms also can leave their mark. Of the estimated 100,000 thunderstorms that occur each year in the U.S., about 10 percent are classified as severe, according to the National Oceanic and Atmospheric Administration. Storms can produce strong wind, sometimes creating tornadoes, and lead to significant damage.

Following are some facts and statistics involving wind-related weather:

• Tornadoes cause an average 70 fatalities and 1,500 injuries in the U.S. each year.
• The strongest tornadoes have rotating winds of more than 250 mph.
• Tornadoes can be 1 mile wide and stay on the ground for more than 50 miles.
• Tornadoes may appear nearly transparent until dust and debris are picked up or a cloud forms within the funnel.
• The average tornado moves from southwest to northeast, but tornadoes have been known to move in any direction.
• The average forward speed of a tornado is 30 mph but may vary from nearly stationary to 70 mph.
• Waterspouts are tornadoes that form over warm water. They can move onshore and cause damage to coastal areas.
• Straight-line winds are responsible for most thunderstorm wind damage; winds can exceed 100 mph.
• A "downburst" is one type of straight-line wind that is a small area of rapidly descending air beneath a thunderstorm. A downburst can cause damage equivalent to a strong tornado and be extremely dangerous to aviation.
• A "dry microburst" is a downburst that occurs with little or no rain. These destructive winds are most common in the western U.S.

This Web exclusive information is a supplement to A preliminary protocol.