When a mass of colder air advances and undercuts warmer air, the boundary is a cold front. The denser cold air forces the warm air upward, often producing a narrow band of showers or thunderstorms along the front itself.

Temperature drops sharply once the front passes. Winds shift, usually from southwest to northwest in the Northern Hemisphere. Pressure reaches a minimum near the front and then rises. The slope of a cold front is steeper than that of a warm front, so the weather change is more abrupt.

Strong cold fronts can trigger severe storms if the warm air ahead is unstable. Weaker ones may bring only a brief period of clouds and light rain. Satellite and radar imagery clearly show the leading edge of these systems as they sweep across a region.

• Cold air advances under warm air
• Produces abrupt temperature falls
• Often accompanied by showers or storms
• Winds and pressure change at passage