Ch 8: Lesson 4: How are Forecasts Made?

Collecting Data• To describe a weather system, you need to describe all its parts; 1. temperature 2. moisture 3. clouds 4. precipitation 5. wind speed 6. air pressure 7. wind direction.

• These parts of weather may change daily or even more than once during the day.

• There are many tools that we use to help us measure all of the parts of weather.

A barometer shows air pressure

An anemometer measures wind speed.

A hygrometer measures the moisture in the air.

A rain gauge measures how much rain has fallen.

Radar can be used to measure the winds and precipitation inside a storm. The radar sends out energy. Some of the energy bounces back from

objects, including raindrops.

Weather Forecasts• One pattern of change in weather is the rising

and falling of temperatures daily. Another temperature pattern occurs throughout the seasons of the year.

• Weather forecasters observe many patterns of weather change. They use their observations of weather patterns to make conclusions about how air, land, and the steps of the water cycle affect each other to make weather systems.

• Forecasters can then predict what the weather will most likely be in the future.

• Forecasters make their predictions by thinking that the weather now will behave like similar weather in the past.

Weather Maps

Forecasters use weather maps to show current weather conditions and predictions.

Weather Symbols

• The triangles or half-circles on a warm or cold front show you the direction the front is moving in.

• Low Pressure areas usually have cloudy weather, and areas of High Pressure usually have clear skies.