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The Building Blocks of Weather

A day’s weather is made up of building blocks, including clouds, precipitation, and wind. The type and intensity of weather is controlled by changes in air pressure.

Air pressure is caused by the weight of the air molecules above. Even tiny air molecules have some weight, and the huge numbers of air molecules that make up the layers of our atmosphere collectively have a great deal of weight, which presses down on whatever is below. This pressure causes air molecules at the Earth’s surface to be more tightly packed together than those that are high in the atmosphere.

Pressure Changes Cause Weather Changes
High pressure causes air to flow down slowly and fan out, moving with clockwise rotation at the ground in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. High pressure days generally have clear skies because sinking air prevents clouds from forming.

Low pressure causes air to flow up slowly. As air rises, it cools and water vapor within the air is unable to remain a gas. It forms tiny water droplets, making clouds in the sky. Remember to bring an umbrella with you on low pressure days because those clouds might cause precipitation.

Delve Deeper...

Monitoring pressure changes