Moderate Santa Ana winds expected this week in L.A. and Ventura counties

Moderate Santa Ana winds are expected to start late Wednesday evening in Los Angeles and Ventura counties, bringing hot, dry conditions to the region and increasing the risk for fast-moving wildfires.

Strong northeast winds will first blow through the mountains of eastern Ventura and western L.A. counties, including the Santa Monica Mountains, and advance to the coasts and valleys Thursday morning, according to the National Weather Service.

In the mountain areas, gusts could reach 60 mph, while the coasts and valleys could see wind gusts between 35 and 50 mph. Temperatures are expected to be in the low- to mid-80s on Thursday and mid- to upper 80s on Friday.

Kathy Hoxsie, a meteorologist in the weather service’s Oxnard office, said winds will be noticeable by midday Thursday and will probably reach their peak late Thursday into early Friday.

Santa Ana wind events occur when high surface pressure builds over the Great Basin region with lower pressure off the Southern California coast, according to the weather service.

Air remains cooler as it moves across the deserts, but as it moves through mountain passes, it becomes compressed and warm. As the wind squeezes through mountains and canyons, wind speed increases, the weather service said.

“It can be difficult to imagine what this is like, but if you think about high pressure as being a high bubble, and low pressure as being a sink area, you can almost picture this flow,� Hoxsie said. “If you put a ball on top of the bubble, it’s going to roll into the sink, and the higher the difference between the high and low, the steeper that gradient and the faster the ball rolls.�