‘Intense’ week-long heat wave coming to Southern California. Here’s the timeline

A heat wave is expected to hit Southern California this week, bringing “elevated” fire danger to the region and increasing the chance for heat-related illness.

The next stretch of hotter temperatures comes after a brief weekend break when most of Southern California enjoyed mild weather.

“We had a brief heat wave over the holiday weekend that was very short in duration where the temperatures weren’t as high,” said National Weather Service meteorologist David Sweet. “This upcoming heat wave is certainly going to be more intense and could be a long duration event, which could continue through the weekend and maybe into next week. We don’t see any end to the heat wave in the next seven days at least.”

High temperatures throughout the region are expected to reach as high as 112 degrees between Tuesday and Saturday. Overnight lows will be in the 70s and 80s.

The coasts will be much cooler, with highs expected in the 70s to mid-80s.

Moisture levels for dead vegetation is around 80% to 100% because of the record rainfall Southern California received over the winter; “critical” moisture levels would be around 60%.

Sweet advised people to avoid all ignition sources and to stay away from anything that could start a fire. In terms of the heat wave, Sweet encouraged people to stay hydrated and stay inside in air-conditioned rooms if possible to limit exposure to the outdoors.

During the heat wave, there is potential for wildfire activity at lower elevations, especially because of the wet weather during the winter and spring and cooler temperatures in May and June, which allowed for a fruitful growing season for plants, UCLA climate scientist Daniel Swain said during a Monday news briefing.

“The fact that we had those cool temperatures is going to be an especially difficult transition, even more so than if we had already been hot,” Swain added.

Here is the forecast timeline for the heat wave:

MONDAY

High pressure is building over the region, bringing dry and warm conditions away from the coast, according to the National Weather Service. On Monday, the marine layer, which tends to keep coastal areas cooler, will continue to shrink under the high pressure, warming coastal plains a few degrees and increasing temperatures into the 80s and 90s for the valleys and around 80 degrees in downtown Los Angeles.

TUESDAY

It’s expected to warm up starting Tuesday for interior parts of Los Angeles County, including the Antelope Valley, Santa Clarita Valley and western San Gabriel Mountains.

An excessive heat warning has been issued for the Apple and Lucerne valleys from Tuesday at 8 a.m. to Sunday at 8 p.m.

Gusty winds could develop across the Antelope Valley on Tuesday afternoon, bumping up maximum temperatures 3 to 6 degrees but bringing temperatures only about 1 to 3 degrees above normal.

WEDNESDAY

Wednesday is expected to be the first day of triple-digit temperatures.

An excessive heat watch has been issued for the western and eastern Antelope Valley foothills starting Wednesday morning through Saturday evening, when temperatures could reach 110 degrees.

Woodland Hills and the Santa Clarita Valley could see temperatures climb from 100 to 103, while the San Gabriel Valley could reach 95 to 100 degrees. Downtown Los Angeles has a projected daytime high from the mid- to upper 80s.

THURSDAY

Valley areas could have daytime highs of around 100 to 105 degrees. The marine layer could still be an influence, resulting in temperatures of 70s into the 80s around immediate coastal sections. Downtown Los Angeles could reach around 90 degrees.

FRIDAY AND THE WEEKEND

The peak of the heat is expected to hit the region Friday into the weekend, with widespread highs around 100 to 108 degrees across the warmest valleys, including Woodland Hills, the Santa Clarita Valley and parts of the San Gabriel Valley.

The hottest areas will be desert regions such as the Antelope Valley, which could see temperatures between 105 to 112 degrees.

Downtown Los Angeles could inch toward 90 degrees.

The heat wave will bring low humidity levels to inland regions, including the Santa Clarita Valley, the Antelope Valley, San Gabriel Valley and San Fernando Valley, resulting in “elevated to brief critical fire conditions,” according to Sweet.

Elevated fire conditions mean that relative humidities are hovering around 15% while critical conditions would signify red flag warnings have been issued and humidity has dropped below 10% for at least six to eight hours, Sweet said.

L.A. County has opened 167 cooling centers — free, indoor air-conditioned facilities — throughout the region. Officials advised people to stay indoors from 10 a.m. to 3 p.m. during the hottest parts of the day, reduce physical activity, avoid hot and heavy meals, check on elderly neighbors and family and friends, and drink plenty of fluids.

The entire Southwest region of the country, including Arizona and New Mexico, is also bracing for a “dangerous” heat wave, which could bring high temperatures to the lower deserts between 106 to 112 degrees this week through Thursday and temperatures between 111 to 117 degrees from Wednesday through this weekend.

A Phoenix resident posted on social media over the weekend, indicating that temperatures were so hot that it was melting the tar off her “newish” roof.