Southern California facing a triple threat: Extreme heat, fire risk and thunderstorms

Grace Toohey, Los Angeles Times on Aug 20, 2025

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LOS ANGELES — As Southern California braces for the most significant heat wave yet this year, officials warn that the dangerously hot temperatures expected at the end of the week are only one of three major concerns.

"It's a trio of impactful hazards affecting Southern California as we head into the next several days: heat, fire and storms," said Ariel Cohen, the meteorologist in charge at the National Weather Service's Oxnard office. "Everyone needs to be getting prepared now."

Extreme heat will build across the Southwest on Wednesday and is expected to bring near-record temperatures to Southern California through the weekend, creating major fire and health concerns. Those threats will be compounded by the possibility of monsoonal thunderstorms that could bring localized flooding, debris flows, destructive winds and lightning beginning Friday.

"The dangerous conditions are going to be coming Thursday and sticking around through the first part of the weekend," Cohen said.

The weather service has issued widespread extreme heat warnings as well as red flag warnings for the mountains and foothills. Temperatures across the Southland are forecast to peak Thursday and Friday, with highs reaching from 95 to 105 degrees everywhere beyond the beaches, and up to 110 degrees in Los Angeles County's interior valleys and deserts.

"Overnight lows will be above 70 in many areas, including downtown L.A.," Cohen said. "That's going to provide little relief from the heat. ... We're talking about significant impacts for anyone susceptible to the heat. Heat-related illnesses are expected to be a major issue, with the potential for fatalities."

Los Angeles officials have joined in calls urging people to make plans to stay safe, including having access to air conditioning, rescheduling outdoor activities, and having several methods to receive emergency alerts. The city announced it had added four cooling centers to its network of libraries and parks that will be open to the public.

"Heat causes more deaths in the U.S. annually than floods, storms, and lightning combined. Those most likely to get ill during the heat include older adults, young children, outdoor workers, athletes, and individuals with chronic medical conditions," said Muntu Davis, Los Angeles County health officer. "If you or someone around you experiences symptoms of heat stroke or heat exhaustion, such as dizziness, nausea, rapid heartbeat, confusion, or passing out, seek medical help immediately."

The excessive and prolonged heat will also create conditions that experts say can fuel extreme and rapid fire growth. Mountains and foothills from San Luis Obispo County south to L.A. County, including the Antelope and Santa Clarita valleys, are under red flag warnings from Wednesday through Saturday, which means an increased risk of wildfires.

"With a low relative humidity and extreme temperatures, the fire environment will be capable of creating extreme fire behavior," Cohen said. Though strong winds aren't in the forecast, some local breezes are expected in the afternoons that could "exacerbate the spread of any plume-dominated fires, and add to the potentially dangerous fire-weather environment," the red flag warnings said.

That fire risk could be further exacerbated by possible thunderstorms Friday through Sunday, when forecasts show a 5% to 30% chance. That monsoonal pattern could bring localized gusty winds, minor flooding, debris flows in burn scars, as well as lightning that could spark fires.

Area fire departments have said they are prepositioning resources and augmenting staffing. The California Governor's Office of Emergency Services said it also sent additional firefighting resources to L.A. County.

"California is taking proactive steps to get ahead of upcoming fire weather," Nancy Ward, CalOES director, said in a statement. "By prepositioning firefighting crews, equipment, and other resources in high-risk areas, we can respond faster and more effectively when needed."

By the end of the week, the heat wave will expand across much of the state's interior, with the San Joaquin Valley, the Sacramento Valley, parts of the Bay Area and the North Coast interior under heat advisories, some extending through Sunday. Highs in the Central Valley are expected to reach up to 106 degrees.

Although forecasters say a gradual cooldown should begin by early next week, temperatures will remain elevated — possibly through the rest of the month.

"Anomalous heat [is] expected to persist across nearly all of California for the rest of August," Daniel Swain, a UCLA climatologist, wrote in a recent blog post. "Warmer than average temperatures will linger into next week and possibly beyond."