TWISTERS Tornadoes also called twisters have terrified people throughout throughout history A tornado is a storm in which powerful spinning winds form a column of air that drops from a dark cloud to the ground Tornado winds are the strongest on Earth They can reach speeds of up to 300 miles 500 kilometers per hour Such violent winds can flatten buildings and whip heavy objects like cars into the air However most tornadoes are short-lived and may not cause much damage 4 A tall tornado in the shape of a cone whips the dirt in a farm field
VOCABULARY Predict means to make a guess based on facts and figures about something that might happen Today meteorologists know a lot about tornadoes tornadoes They can predict where and when a twister is likely to form There are many things they do not know however They often cannot cannot say when a tornado will touch the ground or what path it will take Why only some thunderstorms produce produce tornadoes also remains a mystery The more scientists scientists learn about tornadoes the better everyone can prepare prepare for them and can deal with future twisters Meteorologists use various tools to help them see the path tornadoes followed and the debris they produced 5
STORMY BEGINNINGS It is important to learn about thunderstorms because some produce tornadoes Thunderstorms include thick clouds heavy rain or sometimes hail small lumps of ice lightning thunder and strong winds Thunderstorms form when warm moist air from Earth’s surface quickly rises to cooler parts of the atmosphere There the warm air cools clouds form and rain falls from the clouds Meanwhile the cooled air sinks toward the ground This movement of air causes high winds Violent thunderstorms with thick dark clouds can cover the sky for many miles 6
VOCABULARY Cumulonimbus clouds are puffy clouds that have a low base and are often spread out in the shape of an anvil extending to great heights Cumulonimbus clouds are the source of thunderstorms Sometimes a fast updraft of warm air rises into a cumulonimbus cloud while a downdraft of cool air inside the cloud falls quickly As the warm air and cool air mix they begin to whirl and form a cell or storm center inside the thunderstorm Tornadoes Tornadoes most often develop from strongly rotating cells called supercells 7 Sometimes conditions are right for giant cumulonimbus clouds to form into a thunderstorm
