What is Weather?

Science, Grade 3


Table Of Contents: What is Weather?

1. Our Atmosphere
The Earth is surrounded by a blanket of gases which makes up our atmosphere. Oxygen and water vapor are two types of gases in the atmosphere.
2. Water on Earth
Water covers most of the Earth's surface.
3. The Water Cycle
Water constantly moves from the Earth's surface into the air and back again. This process is called the water cycle.
4. States or Forms of Water
Sunlight provides the energy for water to move through the water cycle. Water changes form when it is heated or cooled. Water can exist as a solid (ice), liquid, or a gas (water vapor).
5. Evaporation
Heat from the Sun causes liquid water on the Earth's surface to change to water vapor or gas. This is called evaporation.
6. Condensation
As this water vapor rises into the air, it cools causing the vapor to turn into tiny water droplets and form clouds. This change is called condensation.
7. Precipitation
As these tiny water droplets in the clouds join together they grow too heavy and fall to Earth as rain, snow, sleet or hail. This process is called precipitation.
8. What is Weather?
Weather is what the air is like outside at any one place and time. Weather is a combination of the types of clouds in the sky, air temperature, the amount of water in the air, and wind.
9. Who studies weather?
Scientists who study the weather are called meteorologists.
10. Measuring Weather Conditions
Meteorologists use various tools to measure weather conditions and predict future weather.
11. Sky Condition
Sky condition is observed using your eyes. The sky can be sunny, partly cloudy, or cloudy.
12. Types of Clouds
The types of clouds in the sky can tell us the kind of weather we will have.
13. Types of Clouds - Cirrus Clouds
Cirrus clouds are thin and form high up in the atmosphere. They often tell us that the weather is about to change.
14. Types of Clouds - Cumulus Clouds
Cumulus clouds are fluffy and look like pieces of floating cotton. They usually predict fair weather, unless they form into stormy cumulonimbus clouds.
15. Types of Clouds - Stratus Clouds
Stratus clouds are smooth, gray clouds in layers that cover the entire sky. Sometimes they produce a light rain or snow.
16. Precipitation
Water that falls to the ground from the clouds is precipitation. Precipitation can be in the form of rain, snow, sleet or hail depending on the air temperature between the clouds and the ground. A rain gauge is used to measure how much water has fallen.
17. Humidity
Humidity is the amount of water vapor in the air. The air feels dry when the humidity is low and damp when the humidity is high. A hygrometer is used to measure the amount of water vapor in the air.
18. Air Temperature
Air temperature is how hot or cold the air is. Temperature is measured in degrees Celsius (oC) or degrees Fahrenheit (oF), using a thermometer.
19. Air Pressure
The air in the atmosphere is pulled toward the Earth's surface by gravity. The weight of the air pushing down on the Earth's surface is the air (barometric) pressure. A barometer is a tool used to measure air pressure.
20. Wind Speed and Direction
Air that moves from one area to another is called wind. Differences in air pressure and heat from the Sun cause winds.
21. Wind
A wind meter (anemometer) is used to measure how fast the wind blows. A wind vane shows the wind direction from which the wind is blowing.