Fog is a cloud in contact with or j

Fog is a cloud in contact with or just above the surface of land or sea. It can be a major environmental hazard. Fog on highways can cause chain-reaction accidents involving dozens of cars. Delays and shutdowns at airports can cause economic losses to airlines and inconveniences to thousands of travelers. Fog at sea has always been a danger to navigation. Today, with supertankers carrying vast quantities of oil, fog increases the possibility of catastrophic oil spills.
The most common type of fog, radiation fog, forms at night, when moist air near the ground loses warmth through radiation on a clear night. This type of fog often occurs in valleys, such as California's San Joaquin Valley. Another common type, advection fog, results from the movement of warm, wet air over cold ground. The air loses temperature to the ground and condensation sets in. This type of fog often occurs along the California coast and the shores of the Great Lakes. Advection fog also forms when air associated with a warm ocean current blows across the surface of a cold current. The thick fogs of the Grand Banks of Newfoundland, Canada, are largely of this origin; because here the Labrador Current comes in contact with the warm Gulf Stream. Two other types of fog are somewhat more unusual. Frontal fog occurs when two fronts of different temperatures meet, and rain from the warm front falls into the colder one, saturating the air. Steam fog appears when cold air picks up moisture by moving other warmer water.