Inversions

Usually temperature decreases with height by approximately 5.5 C per km But with high pressure, clear or near clear skies, and light winds, radiational cooling at the surface can produce INVERSIONS. Inversions are when temperature increases with height. Surface-based inversion range from meters to hundreds of meters in depth

Satellite photo of the Pacific Northwest at 12:45 PM on 20 November (b) Sea-level pressure map valid at 10 AM on 20 November 2005

Field Trip Observations that day from aircraft and at mountain stations indicated that the fog and low clouds over western Washington had bases between 100 and 300 feet and tops around 1200 feet. A layer of cool air, with temperatures of approximately 45F was found in the lowest ft, above which the temperature warmed rapidly with elevation (the inversion). By 2000 ft, temperatures had reached 58F! At Paradise Ranger Station (elevation 5500 ft) and other mountain locations temperatures reached the mid- sixties that day.

Field Trip Drove to the upper reaches of Cougar Mountain, at whose summit is Cougar Mountain Regional Park, with a high point of approximately 1450 feet. Breaking out of the fog at 1200 ft (where the temperature was in the mid 40s), I climbed 300 more feet where the temperature felt in the mid- 50s

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