How does fog begin to form?

Fog primarily forms under conditions of high humidity, often when the air near the surface cools and condenses. The correct choice highlights that fog can begin at a specific height above the ground, which is significant in understanding how and where fog typically develops. Clouds and fog both form through the condensation of water vapor, but the key differentiator is altitude; clouds often form at greater heights, while fog forms close to the ground, leading to reduced visibility.

High humidity levels are a critical factor in fog formation; when the humidity reaches nearly 100%, the air becomes saturated, and when it cools, the moisture condenses into tiny water droplets, creating fog. While it’s generally true that fog can form under various temperature conditions—not solely cold—it primarily transpires when the humidity is high. Understanding this atmospheric behavior helps explain why fog is more prevalent in specific locations or weather patterns, regardless of actual temperature values.