1. What Causes Weather?

2. Weather Scientists gather information about: Temperature Water vapor Wind Air pressure

3. Scientists who study weather are called meteorologists. They use this information and try to guess what the weather will do.

4. Weather is: All the conditions of the atmosphere at a certain time and place.

5. These conditions include temperature, amount of water vapor in the air, wind, and air pressure.

6. Humidity The amount of water vapor in the air is called humidity. When there is a high level of humidity, the air feels sticky and wet.

7. Temperature The measure of how hot or cold the air is.

8. Wind Moving air

9. Air Pressure The weight of air as it presses down on Earth

10. Air Mass Each place on Earth warms or cools the air above it. This creates and air mass. An air mass is a large body of air that has about the same temperature, air pressure and moisture.

11. Fronts Most changes in weather occur when one air mass moves into place and pushes out another air mass. The place where two air masses meet is called a front. A warm front forms as a warm air mass pushes up into a cold air mass. Cold fronts can often cause thunderstorms and tornadoes.