Even at night, SoCal sees little cool down from heat wave

LOS ANGELES — A sweltering heat wave that’s baked parts of Southern California with triple-digit temperatures during the day continues to punish the region with an unrelenting heat that continues after dark.

Temperatures in the Santa Monica Mountains didn’t drop below 95 degrees from Thursday night to Friday morning. At midnight Thursday, it was still 100 degrees in Malibu Hills. Lower elevations along the coast, including Redondo Beach and Huntington Beach, saw a bit of a cool down, but it was still balmy with temperatures in the 70s at night. Inland Los Angeles County ranged from the mid-70s to the high 80s at midnight, according to the National Weather Service.

While it’s not uncommon to have high overnight temperatures during heat waves this time of year, it can prove uncomfortable, said Ryan Kittell, a meteorologist with the National Weather Service in Oxnard.

“What happens is we get our marine layer squashed so low, that really warm and dry layer we have above the marine layer now gets into the populated areas as opposed to being way up in the mountains,” he said. “This time of year when we have these heat waves, it’s pretty common to have those high overnight temperatures.”

Daytime temperatures, while sweltering, have not been record-shattering in most places. This is because a heat wave in 2020 brought slightly higher temperatures to much of Southern California.

On Thursday, the mercury climbed to 121 degrees in Indio, breaking a daily record of 120 degrees that was set in 2020. The Hollywood Burbank Airport tied an all-time high temperature record of 114 degrees that was set in 2018 and reached again in 2020.

Overnight temperatures have been a different story.

University of California, Los Angeles climate scientist Daniel Swain said that while overnight temperatures usually don’t make headlines, they actually have a significant effect during heat waves, both on public health and on firefighters’ ability to combat wildfires.

“From a health perspective they’re disproportionately important, because it’s usually the time most of us are asleep and our metabolic rates decrease. If it’s not cool enough during that period we don’t get that recovery, and so we go into the next day at an elevated level of physiologic stress, and if it’s hot again you can see how the stress accumulates day on day,” he said.

The lower temperatures that usually occur when the sun is down overnight remain about 10 to 15 degrees above average across Southern California, said Chandler Price, a meteorologist with the National Weather Service in San Diego.

On Thursday, Palm Springs’ overnight low hit 92 degrees, tying a record set in 2022. On Friday morning, Indio’s overnight low reached 93 degrees, besting a record of 91 degrees set in 2022. Los Angeles International Airport’s low was 73 degrees, tying a record set in 2022. Palmdale’s low reached 74 degrees, tying a record set in 1974.

Temperatures in Woodland Hills only got as low as 73 degrees on Friday morning, besting a record of 72 set in 2020. The mercury in Burbank reached a low of 82 degrees, breaking a record of 80 degrees set in 2020, according to the National Weather Service.

“Most of the time we think it’s going to be super-hot all afternoon and evening, but it’s going to drop off overnight,” Price said. “We’ll be able to open the windows and set some fans up, and we’ll be all good. But that’s just not happening. The heat never stops.”

This can result in serious health risks for vulnerable populations who don’t have access to air conditioning in their homes and can’t cool off at night.

High temperatures kill more people in the United States than hurricanes, tornadoes, floods or cold weather. When it’s hot, the human body works to cool itself by sweating, but during extreme heat a person’s body temperature can rise faster than its ability to cool itself. This can lead to heat exhaustion and heatstroke, according to the U.S. Centers for Disease Control and Prevention.

When the heat is unrelenting overnight, the human body doesn’t have a chance to take a break, which can place a strain on organs and lead to a variety of issues such as heart attacks, experts say. Outdoor workers, older people, young children, and those who are sick or unhoused are particularly vulnerable to the drastic temperatures.

“The thing about having a high low temperatures is that it means you’re already warm in the morning, and you’re only getting hotter with the sun,” Price said.

The soaring temperatures in Southern California are not unique to this region. International climate officials have confirmed that this summer has been Earth’s hottest on record. The global average temperature in June, July and August was a record-breaking 62.24 degrees, according to the European Union’s Copernicus Climate Change Service.

Temperatures throughout the weekend are expected to remain searing across Southern California.

The mercury in downtown Los Angeles and at Long Beach Airport is expected to reach 99 degrees on Saturday, and LAX is expected to reach 86 degrees. Pasadena and Burbank will really cook at 110 degrees and 108 degrees, respectively. Woodland Hills is expected to reach 114 degrees, according to the National Weather Service.

Triple-digit temperatures are also forecast for much of the Inland Empire, including 109 degrees in San Bernardino. In Orange County, it’s expected to reach 101 degrees in Anaheim and 95 degrees in Irvine.

The National Weather Service has issued an excessive heat warning across much of Los Angeles County, alerting residents of dangerously hot conditions with temperatures up to 115 degrees and overnight lows in the 70s and 80s through Monday night.

High overnight temperatures pose an additional hurdle for firefighters. When temperatures remain high and humidity stays low overnight, fires that typically would become less active during the night have the potential to rage out of control.

“If fire is active day and night, it can spread day and night,” Swain said. “So it takes essentially half as long for fire to spread a given distance than if it was only really advancing during the day and kind of slowing down at night. So it means that they expand faster, move into populated areas — potentially faster — and at night, when it’s more difficult to mitigate the risks.”

The lack of overnight cooling during the heat wave presented a challenge for firefighters battling the Line fire in San Bernardino County this week.

The fire, which broke out around 6:30 p.m. Thursday and prompted evacuations, continued to burn Friday, expanding to more than 500 acres by morning, according to the California Department of Forestry and Fire Protection.

Firefighters rushed to evacuate residents in the city of Highland overnight into early Friday when the flames began racing toward homes. No damage had been reported by Friday afternoon, but the blaze was not contained.

The weather service has issued a red-flag warning for the Santa Monica Mountains, the Santa Susana Mountains and the San Gabriel Mountains, warning of high fire danger brought on by the continuing heat.

Significant cooling likely won’t be felt until at least Wednesday, when temperatures in Los Angeles and surrounding areas are expected to drop to the low 80s and high 70s.