Santa Ana winds pummel southern California; Pasadena declares state of emergency

Tree attacks gas station in Pasadena, California
This does bring back memories--I lived only a few blocks from
here when I was a grad student at Caltech!
Photo by KTLA published in the Los Angeles Times

Updated: 9:20 a.m. CST Thursday 12/01.
Updated: 7:15 p.m. CST, Thursday 12/01.

Wind gusts up to 97 miles per hour are pummeling southern California, causing fires, downing electrical wires, and toppling trees. (Update: Winds up to 140 miles per hour have been recorded at the crest of the Sierras). According to the LATimes, firefighters were being dispatched every 12 seconds in response to emergency calls on downed electrical lines. As of this morning, over 25,000 people are without power, and the winds are expected to continue through Thursday. LA airport was having problems with debris on the runways, but flights are being allowed to land. Update: Pasadena has reported up to 200,000 people without power, and has closed schools and libraries until further notice.

Raymond Chandler described these winds in his 1938 novel, "Red Wind": 

"There was a desert wind blowing that night. It was one of those hot dry Santa Anas that come down through the mountain passes and curl your hair and makes your nerves jump and your skin itch. On nights like that every booze party ends in a fight. Meek little wives feel the edge of the carving knife and study their husbands' necks. Anything can happen. You can get a full glass of beer at a cocktail lounge."

Santa Ana winds are one type of wind called "katabatic" winds. Katabatic is derived from the Greek word "katabatikos" meaning "going downhill." They occur in numerous places around the world.  In southern California they form when air flows from the Great Basin of Nevada westward to the Pacific Coast. As the air flows downhill, it compresses and becomes denser. This compression causes the air to warm and in the summer the winds feel like a blast from a furnace. In the winter, however, this process isn't strong enough to overcome the fact that the air is very cold when it starts from the Great Basin and the winds can bring some of the coldest weather of the season into LA.  The temperatures were down in the forties last night.

Although there was only one fire yesterday and it was quickly controlled, Santa Anas in the autumn can be extremely dangerous--the humidity is low, abundant summer vegetation dries out, and the winds can fan huge fires if they get out of control. The LA fire department has boosted its staffing and declared a "red flag warning" of high fire danger. The Santa Anas are also dangerous to peoples health because they can carry a pathogenic fungus spore that causes Valley Fever (Coccidioidomycosis), an influenza like condition.

Update: More meteorology: There is a counter-clockwise low-pressure system parked over California, and a clockwise high-pressure system over Arizona, Nevada, and the Great Basin. These two systems are funneling the winds into California.  Here's an AccuWeather update. The winds are expected to continue into Friday. Pasadena seems to be the "epicenter" of the storms.