Extended heat wave bakes Southern California mountain, valley areas, adds wildfire risks

Heat warnings and advisories were issued around the region, with temperatures 10 degrees above average projected through much of the week.

Dangerously hot and dry conditions around Southern California are expected to last until the middle of this week, with heat advisories issued for mountain and valley areas in Los Angeles County and the Inland Empire and more wildfire risks seen throughout the region.

In the eastern San Gabriel Mountains, including Mt. Baldy and a portion of the Angeles National Forest, an excessive heat warning will remain in effect until Thursday evening, July 25. Temperatures are projected to reach up to 110 degrees in some areas, with highs from 90 to 100 in lower elevations.

That heat warning was noted by fire officials as more than 180 firefighters continue to battle the 330-acre Fork fire in the Angeles National Forest, reported at 30% containment as of Sunday afternoon.

Heat can dry out vegetation and make it more difficult to put out fires, but wind and low humidity are also major concerns. And even moist air can bring storms, along with lightning.

The dry layer below the clouds forming Sunday above the San Gabriel Mountains could cause rain to evaporate before it reaches the surface, leading to an increased risk of so-called dry lightning, which is “really good at starting fires,” National Weather Service meteorologist John Dumas noted.

There is a 20% chance of thunder and lightning reaching the area from Monday through Wednesday, Dumas said.

A heat advisory issued for the western San Fernando Valley will continue until Thursday, with temperatures ranging from 98 to 103 degrees and at times as high as 105. Woodland Hills and Calabasas could see some of the hottest weather, NWS meteorologist David Gomberg said.

In the San Gabriel Valley, temperatures will remain “quite warm” with highs in the upper 80s to mid 90s. Downtown Los Angeles and inland coastal areas, including Long Beach, will be slightly cooler with highs in the upper 70s and 80s. Temperatures should begin to slightly go down a few degrees by Friday before cooling down on Saturday, Gomberg said.

Heat advisories also have been issued in the Inland Empire, Riverside County and San Bernardino County Mountains, where temperatures roughly 10 degrees above average are projected for most of the week. Eastern and southern portions of the Inland Empire, including Lake Elsinore, Hemet, and San Bernardino could see temperatures reaching 104 to 106 degrees in the next few days, NWS meteorologist Adam Roser said.

Another hot day expected tomorrow! If you plan to spend time outside, make sure to bring lots of water and take breaks in the shade! The coast may offer ~some~ relief, but those looking to escape to the mountains will still find well above normal temps tomorrow. #cawx pic.twitter.com/5tUQAhrXQu

— NWS San Diego (@NWSSanDiego) July 21, 2024

Mountain areas, including Lake Arrowhead, Crestline and Big Bear Lake, could reach between 90 to 100 degrees at elevations below 6,000 feet. By the end of the week, temperatures in the Inland Empire should begin moving down to the upper 90s, Roser said.

The Inland Empire and neighboring mountains have been affected by a heat dome, a high-pressure system that traps heat in the atmosphere. This particular heat dome is centered in Las Vegas, but the impact stretches into Arizona, coastal waters and the southwest. “It’s much more persistent and stronger than normal,” NWS meteorologist Ivory Smalls said.

The average high temperatures are a couple of degrees above normal, according to Smalls, who added that since June 21, it’s been 90 degrees or warmer every day in Ontario except for one, which is unusual.

No heat advisories have been issued in Orange County, which has been spared from the heat wave. Sunny, partly cloudy weather is expected this week, with highs in the mid to upper 70s near the beach. Monday and Tuesday are expected to be the warmest this week, with highs of up to 88 degrees towards the coast and up to 94 degrees further inland, including 91 degrees in Anaheim and 86 degrees in Irvine on Monday.