Educational film continues to explain how weather works, particularly warm fronts. Shot of map with all six air mass regions. Shot of blue skies as narrator explains, "most changes in weather come about when different air masses come in contact with one another." Shot of air masses map again. Shot of weather map with red line. Shot of diagram of warm front with warm air above cold air. Shots of different types of clouds which would occur. Shot of busy city in the rain. Shot of highway in the fog. Another shot of clouds. Shot of tops of trees and clear skies as narrator describes, "when the warm front has passed, and the warm air has completely replaced the cooler air, the weather is usually clear, warm, and humid."