Fast Facts for the Temperature Team

Generally, weather systems move across the United States from the west to the east.
Fronts are narrow zones between two air masses. The air masses have different temperatures, humidity, or both. Clouds and precipitation often form along a front.
Cold air is more dense than warm air. A cold front moves like a bulldozer. It pushes up a warm air mass in its path. The cold air advances, and the warm air retreats.
Warm air is less dense than cold air. That means a warm front slides over top of a cold air mass. The warm air advances, and the cold air retreats.
Warm air is less dense than cold air. That means cold air pushes warm air up. Next, the warm air rises until it eventually becomes cold. That makes it dense enough to move downward.
Unstable air has warm air near the ground and cold air above. Unstable air can lead to billowing clouds and storms.