Fog is also a consideration when planning a morning arrival into an airport where conditions are ideal for fog formation.

Radiation, advection, upslope, and steam are four common types of fog formation. Radiation fog is created when condensation forms after the air temperature near the ground reaches (or nearly reaches) the dew point. This type of fog is often found in valleys when there is no wind. Generally, this type of fog will "burn off" soon after the sun rises and warms the air.

When wind is present in coastal areas, that wind can move warm and moist air over cooler air near the surface, causing what is called advection fog. Upslope fog also requires wind but is found in mountainous regions. The wind pushes the warm air up over the terrain. These two types of fog are not as likely to burn off as is common with radiation fog. Instead, advection and upslope fog could last much longer, and pilots may need to make alternate plans if these conditions are forecast.

The fourth type, steam fog, involves cool, dry air, rather than warm, moist air like the others. It forms when cold, dry air moves over warm water. It looks like steam rising off the water, and you can expect turbulence and icing if steam fog is present.

Pilots who regularly fly in regions where fog is common become accustomed to these patterns and learn to plan their flights accordingly. For new pilots, speaking to local pilots who are well-acquainted with the weather patterns can provide a tremendous opportunity to learn from their expertise. They have a wealth of knowledge and are happy to pass that information on to help others.

In addition, Chapter 12 of the Pilot’s Handbook of Aeronautical Knowledge provides information about fog and other weather conditions.