Thunderstorms Possible As Heat Wave Bakes Orange County

ORANGE COUNTY, CA — Wide swaths of Southern California will bake in triple-digit heat as a heat wave settles over the region into the work week.

The National Weather Service issued a heat advisory for the valleys and deserts as a high-pressure system builds across the West.

The weather service issued a heat advisory from 10 a.m. Sunday to 8 p.m. Monday for inland Orange County, the mountains and the deserts.

The heat wave, combined with low humidity, will lead to elevated fire risks for the mountains and deserts Sunday and Monday. The above-average heat will produce critical conditions in the windiest areas, according to the weather service.

Temperatures were expected to soar above 100 degrees Sunday, Monday and Tuesday, creating life-threatening conditions for vulnerable people in some areas. The National Weather Service issued heat advisories across the hottest parts of the Southland.

In inland Orange County, highs were expected to linger in the upper 80s and lower 90s for the next few days. According to AccuWeather, the Monday high was forecast to be 90 degrees in Mission Viejo, 91 degrees in Rancho Santa Margarita, 87 degrees in Los Alamitos and 95 to 102 degrees in the Santa Ana mountains and foothills.

Orange County's coastal areas will largely escape the heat, with a high of 77 degrees forecast in Laguna Beach Monday, 79 degrees in Newport Beach, 76 degrees in Dana Point, 78 degrees in san Clemente.

Monsoonal moisture may filter into the deserts Sunday afternoon, with a deeper surge expected Monday, forecasters said. Weak easterly waves moving along the southwestern coast might lead to widespread shower and thunderstorm activity in the Southland's mountains and deserts during peak heat hours in the afternoons Monday into the middle of the week.

The very warm and dry conditions will produce elevated fire weather conditions through Tuesday, with brief critical conditions in the windiest areas, according to the weather service.

Temperatures were expected to drop to less dangerous levels beginning Wednesday and to stay relatively mild heading into the weekend.

"Warm temperatures can quickly rise to dangerous levels — especially in the summer and in parked cars. Stay #WeatherReady and don’t underestimate the heat," the National Weather Service tweeted. "Children, the elderly, and those with chronic illness are especially vulnerable to heat exposure."

As usual during heat waves, forecasters urged people to drink plenty of fluids, seek out air conditioned spaces and check in on vulnerable relatives and neighbors.

"Extreme heat will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities," according to the weather service.

"Young children and pets should never be left unattended in vehicles under any circumstances. This is especially true during warm or hot weather when car interiors can reach lethal temperatures in a matter of minutes."

City News Service contributed to this report.