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Air takes up space, and air has weight. When air presses down on the surface of the earth, it causes air pressure. This air pressure is what makes fronts move. Cold and warm air are moving through the atmosphere all the time. Cold masses of air push warmer masses of air out of the way, moving them. When cold air and warm air meet, the weather changes, creating an invisible kind of line between the two kinds of air. This line where they meet is called a front.
If warm air catches up to cold air, it forms a warm front. Warm air is lighter than cold air, and it rises. When it rises, it forms clouds and rain begins to fall. When cold air catches up with warm air, a cold front forms. The warm air rises because the cold air pushes it up. Clouds form again, and heavy rain may fall. This causes thunderstorms. Thunderstorms are caused because hot, moist air rises fast and then cools quickly. Sometimes there is lightning and thunder with a thunderstorm. Thunder is made when air expands suddenly. This is caused by lightning, which is just a huge electric spark that heats the air.
Lightning may look really big, but it’s actually just about one inch around. It can travel up to 10 miles to reach the ground. It moves fast (up to 60,000 miles each second). Lightning doesn’t always touch the ground. Sometimes it happens between two clouds. This is called cloud-to-cloud lightning. Lightning makes the air around it hot. This is what causes thunder, and the closer the lightning is, the louder the thunder will sound. To learn more about fronts, visit this
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