Download Ch8 Lesson 3 PowerPoint

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.