How does fog form?

CEDAR RAPIDS, Iowa (KCRG) - Fog, a common occurrence, especially as we head into August. How does fog form?

Fog is low-lying clouds or a collection of water droplets suspended in the air near the surface.

The most common type of fog that we see here is radiation fog. Fog is most likely to form the morning when there is a lot of moisture around. This keeps the soil saturated and the water will evaporate. You want a small dew-point depression or the difference between the temperature and dew point.

Once you cool overnight, the temperature and dew point becomes closer. When they are near the same value, fog forms.

You also need clear skies and light wind. Clear skies promote the evaporation of the moisture in the ground. Light winds cause moisture to stay at the surface. They also allow temperatures to cool faster, which allows a smaller dew-point depression.