Earth Science Reading Lesson · Grades 4–7

Weather Fronts

A reading lesson on weather fronts. Students learn how giant air masses form, how they meet to create cold fronts, warm fronts, stationary fronts, and occluded fronts, and how each is shown on a weather map.

Reading Passage

Weather Fronts

Have you ever wondered what all those symbols are on a weather map? The curved lines with triangles or circles are fronts moving across the area. Giant air masses form all over the Earth. The sun heats the ocean around the equator, and the warm, moist air rises. As it moves away from the equator, it cools and sinks. Cooler air is drier. When two large air masses meet, a front is formed. Fronts usually bring changes in the weather.

A cold front is made of cold, dense air. On a weather map it appears as a blue line with triangles, with the triangles pointing in the direction the front is moving. When a cold front meets warm air, it forces the warm air upward. As the warm air rises and cools, the moisture in it condenses into clouds and rain. Cold fronts often bring brief but intense rain, snow, thunderstorms, and sometimes tornadoes.

A warm front is shown as a red line with half circles. Warm fronts form when a large mass of warm air takes over a cooler air mass. They cause thick clouds and rain that can last one or two days. The temperature stays warm, and rain or snow tends to be light but steady.

When two air masses meet and neither one takes over, the result is a stationary front. These bring some clouds and a small amount of precipitation. They are shown on the map as a blue line with triangles on one side and red half circles on the other.

Sometimes a fast-moving cold air mass crashes into a warm front, trapping the warm air between two cold air masses. This is called an occluded front, shown as a purple line with both triangles and half circles. Occluded fronts often produce heavy rain or snow.

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