On a weather map, a cold front is drawn with a blue line and blue triangles to show the boundary between two air masses. Northwest winds carry colder and drier air into an area and replace a warmer air mass. As the cold front moves forward, it pushes under the warm air and forces it to rise. If there is enough moisture in the air, clouds will begin to form and rain will soon follow. Sometimes there is even the potential for severe weather to form.