Under what condition does fog or cloud typically form?

Fog or cloud formation is most closely associated with the condition where the spread between temperature and dew point is within 2°C. This proximity indicates that the air is nearly saturated with moisture, which is essential for the formation of these weather phenomena. When the temperature approaches the dew point, the air can no longer hold all of its moisture, leading to condensation. This process results in the formation of tiny water droplets that we perceive as fog when it occurs at ground level or as cloud when it’s higher in the atmosphere.

In contrast, other conditions mentioned do not directly lead to fog or cloud formation. For instance, formation does not necessarily rely on freezing temperatures or high winds, nor does it occur exclusively during high humidity. While high humidity contributes to the likelihood of cloud or fog, it is the temperature and dew point relationship that is a more precise indicator of condensing moisture, making the given choice the most accurate for this situation.