Triple-digit temperatures on deck as heat wave descends on SoCal, elevating fire, health concerns

A major heat wave is set to crank temperatures up across inland Southern California this week, with some areas bracing for triple-digit highs that officials warn will bring health concerns and elevate the fire threat.

Temperatures in some parts of the San Fernando Valley, Los Angeles County’s deserts and the Inland Empire could reach into the high 90s on Tuesday, while the Coachella Valley could hit 114 degrees, according to the National Weather Service.

Things could be even worse on Wednesday and Thursday, with more widespread triple-digit highs forecast for the area’s valleys and deserts.

“Big changes [are] coming ... as high pressure over Arizona expands west into Southern California,” the weather service wrote in a Monday night forecast for Los Angeles. Weaker onshore winds and sinking air from a strengthening high-pressure system “will squash the marine layer to under 1,000 feet by Wednesday and bring significant warming to inland areas and minor warming to coastal areas.”

The heat wave will also decrease the humidity in the afternoons and further dry out an already-parched landscape — a recipe for any spark to turn into a fast-moving fire.

“The hot, dry conditions do make the area a little more prone to fire starts,” said Casey Oswant, a National Weather Service meteorologist in San Diego.

On Monday, three small brush fires sparked in different areas of Riverside County — which has already seen a string of wildfires over the last few weeks — and officials are bracing for more.

“It has been very busy,” said Maggie Cline De La Rosa, a spokesperson for the California Department of Forestry and Fire Protection and the Riverside County Fire Department. “We do expect that to continue because we have a heat wave coming and we do have a lot of dry vegetation.”

But she said crews are staffed and ready: “We’ve been prepared, we remain prepared,” Cline De La Rosa said.

On Monday night, firefighters responded to a fire that ignited in Jurupa Valley that grew to about 45 acres but remained in a rural area, according to Cal Fire-Riverside County Fire Department. By Tuesday morning, that blaze, the Pyrite fire, was 50% contained.

Earlier in the day, the Nichols fire broke out near Interstate 15 near Lake Elsinore, briefly closing one lane of the highway as it reached about 50 acres, according to fire crews. But by Tuesday morning, it was 98% contained. A third fire near Banning grew to about 13 acres, and was completely contained by the end of the day.

The heat wave was also expected to degrade air quality across inland Southern California, creating what officials are warning will be a “multiday extreme ozone [smog] event.” The expected high temperatures and stagnant air work together to trap air pollution in the basin, which can create health hazards for sensitive groups and potentially universally unhealthy air for the Inland Empire and deserts, according to the South Coast Air Quality Management District.

The worst of the L.A. County heat this week is forecast for the San Fernando, Antelope and Santa Clarita valleys, where temperatures are expected to sit in the 90s and potentially push into the triple digits, according to the National Weather Service.

People living in downtown and East Los Angeles can expect to see highs in the 80s to around 90, while temperatures will remain in the 70s along the coast.

The weather will be even more blistering in the Inland Empire, where a heat advisory will be in effect for wide swaths of San Bernardino and Riverside counties from 10 a.m. Wednesday to 8 p.m. Thursday, according to the weather service. The advisory applies to the cities of Corona, Moreno Valley, Ontario, Rancho Cucamonga, Riverside, San Bernardino and Fontana, where temperatures are expected to reach 97 to 104 degrees.

A heat advisory is in effect during the same time frame in inland areas of San Diego County, including the communities of San Marcos, El Cajon, La Mesa, Escondido, Poway and Santee.

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Residents living in these areas are advised to drink plenty of fluids, stay in air-conditioned rooms, stay out of the sun and check up on relatives and neighbors, according to the weather service.

The weather in Los Angeles is largely expected to sit below the heat advisory criteria, in part due to relatively cool overnight temperatures in the low to mid-60s, which will provide several hours of relief. Nevertheless, Angelenos are advised to avoid strenuous outdoor exercise and be aware of the dangers of heat-related illnesses this week.

The heat wave will begin to break on Friday as the high-pressure system weakens, bringing the return of onshore ocean breezes and cooler temperatures. More widespread relief is forecast for the weekend, when temperatures are expected to return to seasonal norms.

But more heat — and more dangerous fire weather — could be in the works for next week as current models show the possibility of an even hotter heat wave coinciding with gusty onshore winds, according to the weather service.