What is the key atmospheric condition required for fog to form?

• A. High temperature with low humidity
• B. High humidity with cooling temperatures
• C. Low atmospheric pressure
• D. Clear skies with high winds

Answer: (B)

Fog formation is primarily driven by the presence of high humidity combined with cooling temperatures. When the air becomes saturated with moisture—meaning it reaches a relative humidity of 100%—the water vapor starts to condense into tiny water droplets, creating fog. This typically occurs in conditions where temperatures drop, such as during the evening or early morning, or when there is a temperature inversion, where warmer air traps cooler air near the ground.

The other options do not promote fog formation effectively. High temperatures with low humidity would generally prevent saturation of the air, thus inhibiting condensation. Low atmospheric pressure does not directly relate to fog but rather influences overall weather patterns. Clear skies with high winds often enhance evaporation and mixing of the atmosphere, typically dispersing fog rather than allowing it to form. Therefore, the combination of high humidity and cooling temperatures is essential for creating the conditions necessary for fog.