How does cold font form?

Answer 1

The cooler, denser air wedges under the less dense warmer air, lifting it, which can cause the formation of a narrow line of showers and thunderstorms when enough moisture is present. This upward motion causes lowered pressure along the cold front.

Source:http://en.wikipedia.org/wiki/Cold_front

http://www.weatherstoreonline.com

Answer 2

Cold front forms when a cold air mass advances and replaces a warm air mass. As the cold air mass pushes the warm air upward, it cools and condenses, leading to the formation of clouds and precipitation along the front. The boundary between the two air masses is where the cold front is typically located.