Cold air masses are large bodies of air that have uniform temperature and humidity characteristics. They typically form over cold regions, such as polar areas or cold ocean waters. These air masses are denser and heavier than warm air, leading to stable weather conditions when they dominate an area. When a cold air mass moves into a region, it can cause a drop in temperature and may lead to various weather phenomena, such as frost or snow. Cold air masses can also interact with warmer air masses, resulting in fronts that can produce storms or precipitation.