Santa Ana Condition Broils L.A.

About a week after it ended officially, summer came to Southern California on Wednesday as temperatures soared well over 100 degrees in parts of Los Angeles, Orange, Riverside and San Diego counties.

Meteorologists said the brief heat wave--which should ease somewhat today and even more over the weekend--was triggered by one of those classic Santa Ana conditions that tend to crop up at this time of year.

“There’s been a big high-pressure system over the Great Basin,� said Stacey Johnstone, a meteorologist with WeatherData Inc., the Wichita, Kan.-based firm that provides forecasts for The Times. “It’s been spinning off those down-slope winds that heat by compression as they move offshore.� The result, she said, is that “you guys have been roasting out there.�

The high temperature Wednesday at the downtown recording station on the USC campus was 102 degrees, 20 degrees warmer than normal and tying the record for the date, set in 1963.

Other top readings Wednesday included 108 degrees in Monrovia and at the San Diego Wild Animal Park near Escondido; 105 in Vista, El Cajon and Anaheim; 104 in Long Beach, Pasadena, San Gabriel, Thousand Oaks, Santee and Fullerton; 103 in Burbank, Ontario, Fallbrook and Riverside; 101 in Northridge, Simi Valley and Van Nuys; and 100 in Arcadia, Glendale and Hawthorne.

Although the readings in Long Beach, Pasadena, Burbank and Simi Valley tied or broke records for the date, the temperatures across the region are not all that startling for this time of year.

As veteran Southern Californians know, some of our hottest weather occurs at the end of September and into early October.

Still, the scorching heat does provide a marked contrast to most of this summer, the coolest in 34 years.

However, Johnstone said the dome of high pressure was starting to break up Wednesday evening, with the mercury expected to drop steadily heading into the weekend.

The high temperature forecast for downtown today is 91 degrees, followed by 83 on Friday, 77 on Saturday and 75 on Sunday. Patches of fog are expected along the coast this morning, with more morning fog moving farther inland Friday, Saturday and Sunday.