Have you ever walked in a cloud? Chances are pretty good you've driven through one. 

Fog is actually just a cloud that forms near the ground, and the fall months are notorious for fog formation.

It can be mystical and dangerous at the same time.

WHAT CAUSES FOG?

Fog is a meteorological phenomenon caused by a supersaturation of the air, so that it can no longer hold water vapor. The water vapor precipitates out into small droplets of condensation, or fog. The processes are similar to those which make clouds, although fog forms close to the ground, rather than higher up in the atmosphere. 

WHY FALL IS SO FOGGY

Since we have mountains, we also have valleys. At night, the heavier, cooler air sinks to the bottom of the valleys and chills the air just enough to form fog, or clouds, near the surface of the ground.

The fall months are a perfect time to find fog, because you often have clear skies, light winds and chilly overnight lows. This allows for the fog to form quickly during the early morning hours.

During fall and early winter the most common form of fog is radiation fog. This type of fog forms when the land cools after sunset by radiating the heat up into the atmosphere. The air must be calm and the skies clear. If there are too many clouds, they can actually act as a blanket to trap in the heat, keeping nights warmer. This is often why cloudy nights are warmer than clear nights.

When the ground is cool, it will cause condensation in the air above it. The more calm the air, the lower the fog is.

During the winter months, fog will form when humid air moves over a cold surface. Winter fog is more common around bodies of water such as our larger rivers and even Smith Mountain Lake.

FOG FOLKLORE

It's often thought that if the number of foggy days in August correlates to the number of snowy days in the winter. As with most folklore, there's nothing that proves this thinking.

Valley Fog Formation