What conditions must be present for air to sit over a location long enough to acquire the characteristics of the land or water beneath it?

Air masses come to have a distinct temperature and humidity when they remain over a region for several days or longer. The heat and moisture leave the ground and move into the air above it, until the overlying air takes on the temperature and humidity characteristics of that particular region.

Explanation:

What happens when warm air and cold air meet?

Warm fronts occur when light, warm air meets cold air. The warm air rises gradually over the cold air as they meet. As the warm air rises it cools and condenses to form clouds. Rain falls along the front as long periods of drizzle or steady rain

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