What happens when a cold air mass meets a warm air mass?

When a cold air mass meets a warm air mass, a front is formed; if the cold air is replacing the warm air, it is known as a cold front. Cold fronts frequently cause rain showers or thunderstorms because they force air in a steep upward direction at the front's edge. They also bring about changes in wind direction and atmospheric pressure.

When warm air replaces cold air, this is known as a warm front. Warm fronts also cause changes in the pressure of the atmosphere and wind direction. However, warm fronts displace air in a more gradual, gentle manner. This results in steady, long-lasting precipitation that affects a wide area.