Explanation:

The well known Polar-front theory was described by the Bergen school early  20th century. The theory explains the formation, development and life cycles of cyclones. In short several stages of cyclone development can separately be identified. The polar front arises as a result of cold polar air meeting warm tropical air.  It is a stationary front as the air masses are not moving against  each other.  Off the coast of eastern North America, especially in winter, there   is a sharp temperature gradient between the snow-covered land and the warm offshore currents.