What Causes a Cold Front?

A cold front is caused by the boundary between warm and cold air, with the cold air mass taking the place of the warm air mass. Cold fronts can occur in the winter and in the summer.

Since the cold air mass is heavier, it pushes underneath the warm air mass as the cold front moves. The warm air rises because it is lighter, and the presence of enough humidity in the air can create water vapor and precipitation. Cold fronts can cause thunderstorms, especially in the summer when there is more humidity in the air. The barometric pressure decreases and then increases, and the temperature can drop more than 15 degrees in one hour after the arrival of a cold front.

On a weather map, cold fronts are usually designated by a curved line with arrows pointing in the direction in which the front is moving. The air behind a cold front is drier and colder than the air in front of it. Before a cold front arrives, the wind moves in a south-southwest direction, the temperature increases and the dew point stays steadily high. After the cold front passes, the wind moves in a west-northwest direction, the temperature drops slowly and the dew point begins to lower again.