Firefighters made progress Saturday in a San Francisco Bay Area blaze that endangered homes and sent residents fleeing as dry, gusty conditions across California raised the risk of wildfires.

The Keller Fire in the Oakland Hills began Friday afternoon and damaged at least two homes. The fire has burned about 15 acres and was at 50% containment as of Saturday morning, according to Cal Fire. About 500 people were ordered to evacuate, the Associated Press reported.

Part of Interstate 580, which runs through the Bay Area, had to be temporarily closed near the scene of the fire but was later reopened. Fire crews stayed at the scene overnight and planned to remain Saturday, Oakland Fire Chief Damon Covington said in a morning briefing.

"The elevated temperatures and the heavy winds are what we're watching out for," he said.

The fire – fueled by strong winds and dry conditions – is believed to have jumped from a vegetation blaze near I-580 to the homes before igniting eucalyptus trees, Covington said. The cause of the fire is still under investigation, but it drew comparisons to Oakland's 1991 firestorm exactly 33 years ago that killed 25 people and destroyed thousands of homes in the Berkeley and Oakland hills, north of Friday's fire.

Conditions then were similar to Friday's fire, Covington said. But he added that equipment was recently positioned to patrol the hills, and Bay Area firefighters were ready before Friday's blaze grew out of control.

"We had pre-prepared for days like this," he said.

Red flag warning issued in Bay Area, Central Coast

California is battling several fires, and the National Weather Service issued a “red flag warning” for dry and windy conditions developing through Saturday afternoon in the Bay Area and Central Coast, just to the south.

This includes winds of at least 25 mph and gusts up to 50 mph. Isolated gusts even stronger in higher terrain and ridges are possible, the National Weather Service office warned Saturday morning. Coupled with winds, the humidity could dip to low digits with temperatures in the high 70s.

On Friday night, power company Pacific Gas & Electric said it had turned off power for a total of about 17,500 customers across 21 counties and three tribes under a “Public Safety Power Shutoff” to prevent power lines from sparking wildfires

. In a Saturday morning update, PG&E said it issued "all-clears" for about half of the affected counties because of improved conditions. This allows crews to assess damage and restore power when it's safe to do so. Other affected areas are expected to have all-clears later Saturday, PG&E said.

Earlier in the week, officials warned that “Diablo winds” would sweep across Northern California and could create conditions ripe for fires. The dry wind – typically in the fall – moves from inland areas to the Pacific Coast. It gets its name from the Diablo Range, just east of Oakland.

Santa Ana winds expected in Southern California

The Diablo winds' counterpart in Southern California are the seasonal Santa Ana winds, which blow hot, dry air from inland desert areas to the Pacific Coast. The Santa Ana winds were in “full swing,” the weather service Los Angeles office said on social media.

These winds, usually in the fall when it’s hot, help wildfires take off in the region. Gusts in Los Angeles and Ventura counties are expected to reach 25-40 mph. Gusts could hit 50 mph and will be strongest in valley hills and mountain peaks, the weather service warned.

The red flag warning issued through Saturday afternoon in Southern California is unlikely to be extended, officials said.

Next week, California is expected to have warmer temperatures with conditions still dry in the heart of wildfire season, said Bob Larson, senior meteorologist at AccuWeather.

"It may not take long for this to flare up again," he told USA TODAY. "The season is definitely not over yet."

California's wildfire season is thought to be from spring through the fall. However, the California Air Resources Board said climate change, caused mostly by burning fossil fuels, is increasing both the frequency and severity of fires. A warming climate is also expected to lengthen wildfire seasons.

(This story was updated to add new information.)