Chapter 8: Lesson 3: What causes severe weather?

Thunderstorms Thunderstorms form in many ways, most often they occur in the following 3 stages: Stage 1: Air currents move upward and clouds form. Stage 2: Air currents are mixed, precipitation begins to fall, pulling some air down with it. Storm now has currents of air moving both upward and downward. Stage 3: All air currents move downward. Clouds get smaller as precipitation falls.

More thunderstorms… • Different areas of a thunderstorm have positive and negative electrical charges. • Lightning is an electrical spark moving between areas of opposite electrical charge. • Lightning increases the temperature of the air which causes vibrations in the air, we hear these vibrations as thunder. • A severe thunderstorm watch means that a thunderstorm MIGHT happen. • A severe thunderstorm warning means severe thunderstorms HAVE formed and you should prepare for them.

Tornadoes! • Layers of wind in a storm blow at different speeds in different directions. • Between these layers, a column of air spins on its side. • One end of the column is lifted by upward winds. The other end is pushed down by downward winds. • The spinning column of air is a funnel cloud. When the funnel cloud reaches the ground it is called a tornado. • Tornadoes only last a few minutes, but they can cause great damage.

Hurricanes • Hurricanes get their energy from warm ocean water. • When water vapor from the ocean condenses, it releases energy. This energy could build and power the winds of a hurricane. • Once over land, the hurricanes energy is reduced. • Winds from a hurricane can be worse than those from a tornado because 1. They last for days, hitting many locations. 2. They are wide storms. 3. Hurricanes can cause huge waves which can cause damage and floods.