1. Chapter 8: Lesson 3: What causes severe weather?

2. 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.

3. 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.

5. 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.

7. 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.