What are two basic ways fog can form?

Fog typically forms when air becomes saturated with moisture, which can occur through two primary mechanisms: cooling the air to its dew point and adding moisture to the air.

When the air cools down to the dew point, the temperature where air becomes saturated with water vapor, condensation occurs and tiny water droplets are formed. This process can take place overnight when temperatures drop, leading to the development of radiation fog.

Adding moisture to the air can also lead to fog formation, especially when warm, moist air meets cooler surfaces or air. This can increase humidity levels to the point where they reach saturation, forming stratus clouds or fog.

Both of these methods effectively create the conditions necessary for fog to form, making the choice regarding cooling air to the dew point and adding moisture to the air the correct answer. Understanding these two processes is critical in aviation, as fog can significantly impact visibility and flight safety.