What occurs when cold dry air moves over warm water, creating steam fog?

When cold dry air moves over warm water, the process leads to the condensation of water vapor, which is the correct answer. As the cold air comes in contact with the warmer water, the water's temperature causes some of the air’s moisture to warm up and evaporate. This process creates water vapor. As the air continues to remain cold, it can only hold a limited amount of moisture. When the increased water vapor reaches the colder temperatures of the adjacent air, it condenses back into small water droplets, forming steam fog. This phenomenon is commonly observed over lakes and rivers, especially during the cooler months when the water temperature is significantly warmer than the air temperature.

In this scenario, while temperature fluctuations do occur, they don't fully encapsulate the primary process of steam fog creation like condensation does. The formation of ice crystals, which is a separate process related to freezing temperatures, isn't relevant when discussing the dynamics between warm water and cold air in the context of steam fog.

Thus, the condensation of water vapor is the fundamental process that leads to the visibility of the steam fog, making it the most appropriate answer.