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In this lesson, we will explore a weather phenomenon known as a cold front. We’ll go over facts about cold fronts, as well as characteristics of and weather patterns that result from cold fronts.

What Is a Cold Front?

Have you ever heard a meteorologist on the news talking about a low pressure system moving into the area and creating gloomy, rainy weather? This kind of weather can be caused by a cold front. A cold front is a body of cold air that moves toward warmer air. Changes in air temperature can cause changes in weather.

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Characteristics

Cold fronts are bodies of air with cooler temperatures than the surrounding air, and they normally move from northwest to southeast. The temperature shift between cold and warm fronts can be drastic, from freezing temperatures near the cold front to warm temperatures close to the warm front. On a weather map, cold fronts are shown as curved blue lines with triangles pointing in the direction that the front is moving.

Cold Front Collisions

To think about the effects of cold air, we first need to understand how warm and cool air move, which is based on air density. When air is colder, the air molecules pack together more tightly, so the air becomes more dense and sinks. This is kind of like what happens when you feel cold. When people get cold, we shiver and pack together, trying to keep each other warm. Cool air does the same thing: it packs together and becomes more dense.Warmer air has air molecules that are more spread out.

Air molecules that are more spread out are less dense and will rise. Think again about the comparison to people. When people are hot, we want to get as far away from each other as possible. The people are like the warm air in this example, spreading out as they heat up. When a cold front meets up with warmer air, the cold air sinks, pushing the warm air into the atmosphere.

Cold Front Weather

The movement of warm air upward is called a low pressure system. To better understand how low pressure systems cause clouds and storms, we need to return to the idea of density. Warm air is less dense and the air molecules are spread apart. Because the air molecules are spread apart, there is more room for water vapor in the air. So, warm air contains more moisture. In cold air, the reverse is true: the air molecules are packed tightly together, so there isn’t much room for water vapor.If we go back to our people analogy, let’s think of water vapor as tables in between the people.

In the room full of warm people, there is more room for tables. But in the room with the cold people, everyone is so tightly packed together that there’s no room for the tables.So what does this have to do with clouds? Remember that warm air is less dense, so it rises, taking the moisture with it.

However, temperatures get colder as we go higher up in the atmosphere, so eventually that warm air cools off and can’t hold the water vapor anymore. The water vapor brought by the warm air starts to form clouds and eventually condenses, or changes from a gas to a liquid, forming precipitation. The same thing happens on a warm day when you have a refreshing, cold drink. The warm, moist air comes in contact with the cold bottle and condenses, or changes into water droplets on the side of the bottle.Cold front weather has the potential to be dangerous.

In severe cases, low pressure systems caused by cold fronts can spawn tornadoes and even hurricanes. Tornadoes are storms with extremely fast, spinning winds, caused by warm air rapidly rising and falling. The spiral pattern of wind connects to the ground as well as the clouds, moving with the storm. Strong updrafts (or warm air rising) combine with strong downdrafts (or cool air falling) to form an intense rotating motion.

Lesson Summary

In summary, a cold front is a body of air that is significantly cooler than the air around it. Cold fronts bring cooler temperatures to an area and can cause changes in weather patterns. Cold fronts typically move from northwest to southeast and are shown as blue lines with triangles on a weather map. A low pressure system is a movement of warm air upward.Cold fronts can cause precipitation, thunderstorms, and even tornadoes.

This happens because of the different densities of warm and cool air. A cold front entering an area forces warm, moist air into the atmosphere, where it condenses to form precipitation. If the force is great enough, the air can cause the air to rotate from the up- and downdrafts, causing a tornado.

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