Boundary between dense, cold air and the warmer air ahead of it, which the cold air tends to undercut as it advances. The gradient of the upper surface of the cold air may be steep, e.g. 1:50. Along this steep front violent upwelling and instability result in high cumulonimbus cloud with rain and thunder. Weather changes occur with the passage of a cold front, sometimes including a pronounced temperature fall, a rise in pressure, and wind veering (often with squalls) to northerly or north-westerly (in the northern hemisphere). The passage of the front commonly brings clearer, brighter weather, but the unstable air can produce showers.
Subjects: Earth Sciences and Geography.