Section 2: Severe Weather All thunderstorms produce wind, rain, and lightning, which can have dangerous and damaging effects under certain circumstances. K What I Know W What I Want to Find Out L What I Learned

Essential Questions Why are some thunderstorms more severe than others? What are the dangers of severe weather? How do tornadoes form? Severe Weather Copyright © McGraw-Hill Education

Vocabulary Review New air mass supercell downburst tornado Enhanced Fujita Tornado Damage scale Severe Weather Copyright © McGraw-Hill Education

Severe Thunderstorms The increasing instability of the air in a thunderstorm intensifies the strength of a storm’s updrafts and downdrafts, which makes the storm severe. Copyright © McGraw-Hill Education Severe Weather

Severe Thunderstorms Supercells Severe thunderstorms can develop into self-sustaining, extremely powerful storms called supercells. These furious storms can last for several hours and can have updrafts as strong as 240 km/h. An anvil-shaped cumulonimbus cloud is characteristic of many severe thunderstorms. Severe Weather Copyright © McGraw-Hill Education

Strong Winds Violent downdrafts that are concentrated in a local area are called downbursts. Based on the size of the area they affect, downbursts are classified as either macrobursts or microbursts. Severe Weather Copyright © McGraw-Hill Education

Hail Hail is precipitation in the form of balls or lumps of ice. It forms because of two characteristics common to thunderstorms. Severe Weather Copyright © McGraw-Hill Education

Hail For hail to form, water droplets rise to the heights of a cumulonimbus cloud where the temperature is below freezing, encounter ice pellets, and freeze on contact with the pellets, which causes the ice pellets to grow larger. The second characteristic that allows hail to form is an abundance of strong updrafts and downdrafts moving side by side within a cloud. Severe Weather Copyright © McGraw-Hill Education

Tornadoes A tornado is a violent, whirling column of air in contact with the ground. When a tornado does not reach the ground, it is called a funnel cloud. Severe Weather Copyright © McGraw-Hill Education

Tornadoes Development of tornadoes A tornado forms when wind speed and direction change suddenly with height, a phenomenon called wind shear. Although tornadoes rarely exceed 200 m in diameter and usually last only a few minutes, they can be extremely destructive. Severe Weather Copyright © McGraw-Hill Education

Add link to Animation from p. 352 here. Tornado Formation Concepts In Motion FPO Add link to Animation from p. 352 here. Severe Weather Copyright © McGraw-Hill Education

Tornadoes Tornado classification The Enhanced Fujita Tornado Damage scale, which ranks tornadoes according to their destruction and estimated wind speed, is used to classify tornadoes. Severe Weather Copyright © McGraw-Hill Education

Add link to Interactive Table from p. 353 here. Fujita Tornado Intensity Scale Concepts In Motion FPO Add link to Interactive Table from p. 353 here. Severe Weather Copyright © McGraw-Hill Education

Tornadoes Tornado distribution Most tornadoes—especially violent ones—form in the spring during the late afternoon and evening, when the temperature contrasts between polar air and tropical air are the greatest. This type of large temperature contrast occurs most frequently in the central United States. Severe Weather Copyright © McGraw-Hill Education

Tornadoes Tornado distribution Many of the more than 1000 tornadoes that touch down in the United States each year occur in a region called “Tornado Alley,” which extends from northern Texas through Oklahoma, Kansas, and Missouri. Severe Weather Copyright © McGraw-Hill Education

Tornadoes Tornado safety If you are caught in a tornado, take shelter in the southwest corner of a basement, a small downstairs room or closet, or a tornado shelter. Severe Weather Copyright © McGraw-Hill Education

Add link to Video from ConnectED here. What's Earth Science Got to Do With It?–Storm Chasers Video FPO Add link to Video from ConnectED here. Severe Weather Copyright © McGraw-Hill Education

Review Essential Questions Vocabulary Why are some thunderstorms more severe than others? What are the dangers of severe weather? How do tornadoes form? Vocabulary supercell downburst tornado Enhanced Fujita Tornado Damage scale Severe Weather Copyright © McGraw-Hill Education