Weekend heat wave to leave L.A. valleys and mountains sweltering

Officials have issued a heat advisory for most of the Los Angeles County valleys and mountains, as well as the Inland Empire, where triple-digit temperatures are forecast through the weekend.

The advisory is in effect through Sunday for the Santa Clarita, San Fernando and San Gabriel valleys, with temperatures forecast to hit 95 to 103 degrees. Temperatures could reach 104 degrees across lower elevations in the mountains.

In the San Bernardino and Riverside county valleys, a heat advisory is in effect through Monday. High temperatures there are expected to range from 98 to 105 degrees.

Residents are advised to hydrate, wear lightweight, loose-fitting clothing and stay indoors between 10 a.m. and 3 p.m., when the sun is strongest. Los Angeles County will be operating cooling centers and has compiled a list of public pools and splash pads.

The heat is expected to peak Saturday as a high-pressure zone extends from the Southwest and lingers over the region, the National Weather Service said. Temperatures should start to cool by Monday, when a trough of low pressure is forecast to move into the area.

Air quality officials also issued an ozone advisory for the South Coast Air Basin through Tuesday morning, saying that the heat will combine with atmospheric inversions to trap smog pollution close to the ground.

Lucas Spelman, a California Department of Forestry and Fire Protection battalion chief, said Cal Fire doesn’t anticipate an unusually high fire risk this weekend because winds aren’t expected to be very strong. Still, he said, if homeowners are planning to undertake any kind of defensible space preparations, such as mowing lawns or trimming trees, it’s a good idea to do so before 10 a.m. to avoid exhaustion and reduce the risk of sparking a vegetation fire.

Residents also are reminded to check in on older friends and neighbors and those who don’t have air conditioning, and to keep pets indoors.

alex.wigglesworth@latimes.com | Twitter:@phila_lex