California’s wildfire season heating up
A series of fast-moving blazes kick-started California’s fire season season this week, a turnaround from a deceptively quiet summer, and one that might signal a relentless autumn. The culprit: a long hot spell, followed by a transition to more turbulent weather.
It started in Southern California, where firefighters wrestled the nearly 2,000-acre Tenaja Fire and struggled to protect homes. Then, in Northern California, winds propelled runaway fires, including the Walker Fire, the year’s largest, at over 44,000 acres and counting. There were evacuation orders in Butte County over the weekend, and again near Santa Barbara on Monday, when brush fires closed parts of U.S. 101. “It’s been a very slow build-up; that’s why it seems so sudden,” said Alex Tardy, a meteorologist at the National Weather Service in San Diego.
After a wet, cool May, the summer months were remarkably calm; dips in the jet stream, or “troughs,” stalled the fire season in California, the Pacific Northwest and the Northern Rockies. However, the state started heating up in late July, and August temperatures were well above average.
Last month’s prolonged heat dried out dead plants and stressed larger live plants and trees, making them more susceptible to fire. In many areas, it’s like the wet winter and spring never happened, because vegetation is back to where it usually is in late August and early September — at peak dryness — and in some regions, drier. This winter’s heavy grass crop ignites easily and burns more intensely, with taller flames.
But the tipping point was a bout with gusty thunderstorms last week, and a high-altitude weather disturbance that is now bringing cooler but dry weather. The Tenaja fire, which threatened neighborhoods in Murrieta, north of San Diego, “was our first major fire here in Southern California all summer,” said Matthew Shameson, a meteorologist with the U.S. Forest Service in Riverside.
Forest service meteorologists expect continued dry and hot weather through the fall, with a chance that Southern California’s fire season could extend well into December. According to the wildfire outlook from the Riverside office, there is no sign of rain on the horizon: “Barring the influence of a dissipating tropical storm, offshore winds will almost certainly arrive before the onset of meaningful rainfall.”
The dry easterly Santa Anas — and their sister winds in Northern California — are the season’s biggest threat. “We’re going to get at least a few; it’s just a matter of how strong,” Tardy said.