Lack of cloud cover and light winds are generally found in high pressure centers, and are prone to exist in fall and winter as longer nights develop. As the air cools, it becomes more dense and heavier than the air around it. The colder, heavier air will drain into low spots like river valleys or depressions. You may be driving along a country road and come up over a hill with clear skies above, and seconds later as you drive into a low spot become swallowed up by a patch of ground fog. Radiation fog processes in river valleys are called valley fogs.
River valleys are very susceptible to radiation fog as cold air drains where moisture is available.
Read more about fog and the different types of fog . TMJ4 is not responsible for the content of external sites links through our site.