"During a foggy summer you tend to have cool conditions along the coast and unusually warm temperatures in the interior," Johnstone said, adding that during less foggy summers coastal areas tend to be warmer than usual and the interior is cooler.
Historically there have been stark temperature differences at times between the coast and areas just a short ways inland. But the differences have been shrinking in recent years, mostly because of rising coastal temperatures, he said. Cooler temperatures typically are located near sea level, and the warmer inland temperatures begin to show up at about 1,300 feet in elevation.
Johnstone found that the contrast between inland and coastal temperatures was much greater from 1900 to 1930 than during the last 60 years, indicating that summers on the coast were much foggier in the early 20th century.
But he notes that while coastal fog has generally declined, the data in general have shown consistent variability. For example, the Pacific Northwest, and Seattle specifically, had record fog frequency in the summer of 2010, and many places along the West Coast recorded their foggiest summer since 1991.
A next step in his work will be to understand the discrepancy between climate models and actual fog observations so that the factors involved in summer fog formation can be better understood.
|Contact: Vince Stricherz|
University of Washington