Private Pilot Private Exam

Which types of fog require wind to exist?

1. Radiation fog and steam fog

2. Advection fog and upslope fog

3. Stratus fog and radiation fog

4. Valley fog and freezing fog

The correct answer is: Advection fog and upslope fog

Advection fog and upslope fog are types of fog that indeed require wind to form. Advection fog develops when warm, moist air moves (or is advected) over cooler surfaces, such as cold water or land. The cool surface lowers the air temperature, causing condensation and the formation of fog. Wind is essential because it brings the warm air in contact with the cooler surface, facilitating the cooling process necessary for fog formation. Upslope fog occurs when moist air is forced to ascend a slope, such as a mountain. As the air rises, it expands and cools, leading to condensation and fog formation. This process also relies on wind to push the moist air upwards. In contrast, other fog types mentioned in the other options do not necessarily need wind for their formation. For example, radiation fog forms during clear nights when the ground cools rapidly, often occurring with little or no wind.