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 2005. (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 700800 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 midsixties 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 mid50s
Seattle Profiler