Weather Wednesday: Valley Fog

FARGO, ND — The James River Valley and the Sheyenne River Valley might not be as grandiose as the valleys in the mountains or along the Mississippi, but they do have one thing in common: valley fog. Valley fog is a type of radiation fog, which is the typical kind of fog we all can get, regardless of where you live. On a clear, quiet night, the heat and energy that the Earth absorbs during the day escapes back into the atmosphere, allowing the temperature near the ground to cool down. As it cools, the air becomes denser, and as a result, it wants to sink. When the terrain is flat, there s really nowhere lower for that air to go, but when you have a valley, that cold air drains down the slope and collects on the valley floor. This is called cold air drainage. The pooling of that cold air down in the bottom of the valley allows the air there to become saturated more effectively than the air at the top, and with the aid of additional water vapor from the val