Cold front
A 'cold front' is a meteorological word that is used to describe the movement of a cooler airmass into an area of warmer air. University of Illinois. The air with greater density moves under the less dense warmer air, lifting it, which can cause a line of showers and thunderstorms, or a squall line to form when there is sufficient moisture. This upward motion causes lowered pressure along the cold front. Cold fronts can also move up to twice as fast as warm fronts.