A fire warning was in effect Thursday for San Diego County and much of Southern California as temperatures were expected to soar as high as 100 degrees amid high fire danger.
The dangerous Santa Anas, typical of fall in Southern California, triggered the warnings for fire danger from coastal counties northwest of Los Angeles down to the Mexico border.
Residents in the mountains and valleys can expect strong, gusty winds and low humidity through the day. Winds were expected to be in the range of 15 to 25 mph with occasional gusts between 35 and 50 mph according to the National Weather Service.
With humidity in the 6 to 10 percent range, any fire that may break out has the potential to spread rapidly.
Santa Anas are spawned by cold air descending on the vast interior area of the West known as the Great Basin. Air flowing from that region of high pressure spills through mountain ranges and down into the metropolitan regions of Southern California.
The winds push back the normal moist and cooling influence of the Pacific Ocean and gain warmth from compression and speed, similar to the way a languid river turns into rapids at a narrows.
The northeast winds have been linked to the spread of some of the region's most destructive wildfires.