June 15, 2003
The above photo of Deception Pass, in Washington state, shows the bridge draped in fog. This type of fog is called “advection fog.” Advection fog is common up and down the Pacific Coast because the water surface along the coastline is colder (when upwelling occurs) than the surface water farther away from shore. As warm, moist air moves over the colder coastal waters, its temperature drops as it is cooled from below. If the air cools to its dew point temperature, as it did on this day, fog forms when the water vapor condenses. See also the Earth Science Picture of the Day for Monday, June 9.
"Deception Pass" was named by Captain Vancouver when he mistakenly thought the island was a peninsula.