Certified Flight Instructor - Flight Instructor Airplane Practice Exam

How does high humidity at night affect fog formation?

1. It prevents fog from forming completely.

2. It contributes to the likelihood of fog development.

3. It simply increases visibility.

The correct answer is: It contributes to the likelihood of fog development.

High humidity at night significantly contributes to the likelihood of fog development. When the air is saturated with moisture, the conditions become more favorable for fog to form, especially when temperatures drop during the night. As temperatures decrease, the air can hold less moisture, which increases the relative humidity. When the air temperature cools to the dew point, condensation occurs, resulting in tiny water droplets that create fog. In conditions of high humidity, especially in still air, the moisture in the air can condense more easily. This is particularly true in low-lying areas where cool air sinks and further increases humidity levels. The formation of fog under these circumstances is a common phenomenon seen during calm, clear nights when the air is saturated with moisture. By contrast, dry conditions would typically inhibit fog formation, as the air would not retain enough moisture to condense into fog. Hence, the role of high humidity is pivotal in enhancing fog development.