A cold front occurs when a cold air mass advances and replaces a warm air mass. Advancing cold fronts force warm moist air to rise sharply, producing showers and thunderstorms during the warm season, and snow during the cold season. As a cold front passes, temperature and humidity drops and air pressure rises.
A stationary front occurs when a cold air mass and warm air mass meet, but neither moves much in any direction. Cloudiness and light to moderate precipitation may persist for days on the cold side of a stationary front as the warm air gradually rises over the cold air.
An occluded front occurs as a cold front overtakes a warm front, and forces the warm air to rise. The cool air mass remains at the surface. Low clouds and light precipitation usually accompany the passing of an occluded front.
Winds will always veer after a front passage. Fronts are named according to the direction of movement of the colder air mass.