By Steve Gorman

LOS ANGELES (Reuters) - Unseasonably balmy weather settled over Southern California on Wednesday as a region already accustomed to celebrating Christmas without snow experienced temperatures some 15 degrees (9 degrees Celsius) above normal.

The warm spell baked the West Coast while the Midwest and Northeast were still dealing with the aftermath of a winter storm. Some 129,000 homes and businesses were without power on Christmas morning, energy companies reported.

Southern California temperatures climbed to record or near-record levels in the upper 70s Fahrenheit (low 20s Celsius) and low 80s (mid 20s Celsius), propelled by warm, dry Santa Ana winds blowing toward the Pacific from the high deserts, meteorologists said.

By midday, the temperature reached 81 degrees Fahrenheit (27 Celsius) in downtown Los Angeles and was expected to top out just short of the city's record Christmas day high of 85 degrees (29 Celsius), set in 1980.

The afternoon warmth followed an overnight low of 47. Temperature records for the city date to 1877.

The city of Long Beach, about 20 miles south of Los Angeles, saw the temperature soar to at least 83 (28 Celsius), 2 degrees Fahrenheit above the 1972 record for Christmas Day, according to National Weather Service meteorologist Curt Kaplan.

Daytime highs also were forecast to approach record levels in Burbank and San Diego. Southern California's normal daytime highs range in the mid- to upper 60s (18 to 20 Celsius) this time of year.

The region's coastal conditions likewise brought little Christmas cheer, with low waves expected to frustrate surfers who traditionally wear Santa Claus costumes to ride the swells at this time of year.

Capping a year of scant rainfall, the arrival of Santa Ana winds also prompted the Weather Service to post a "red flag" advisory for much of Los Angeles and Ventura counties, warning of a high risk of wildfires due to dry, blustery conditions.

The Santa Anas arise when a high-pressure area forms over Utah and Nevada, producing a strong, westerly air flow that heats up sharply as it blows through the desert mountains of southeastern California and descends into the coastal basins below, meteorologist Mark Moede said.

The winds were thought to have contributed to power outages that left some 5,000 homes without electricity Wednesday morning in Simi Valley, north of Los Angeles. Most customers were reported back on line by midday, according to Southern California Edison.

(Additional reporting by Curtis Skinner; Editing by Daniel Trotta and Bill Trott)