LOS ANGELES >> Temperatures are expected to hit triple-digit territory in the San Fernando and Antelope valleys and come close to doing the same in the Santa Clarita Valley as the Southland’s weekend heat wave continues at a time when there are also with exceedingly unhealthy smog levels.

The National Weather Service forecasts a mix of partly cloudy and sunny skies in Los Angeles County Saturday with temperatures ranging from the mid 80s to triple digits.

Temperatures will stay roughly the same in most of the county over the next several days, retreating slightly beginning Thursday, although the Antelope Valley will buck the trend with steadily increasing temperatures until Wednesday. According to a NWS forecast, Lancaster will hit 104 Saturday, 107 Sunday, 108 Monday, 110 Tuesday, 107 Wednesday and 103 Thursday.

Sunny skies were also forecast in Orange County with highs in the 70s to mid 90s. Temperatures will stay roughly the same at least for the next six days.

NWS forecasters blamed the high heat on strong high pressure over Western States and said it would cause temperatures to be 12-18 degrees above normal throughout the weekend, with the Antelope Valley boasting the warmest temperatures.

An excessive heat warning will be in force in the San Gabriel Mountains from 11 a.m. Saturday until 9 p.m. Wednesday, in the Antelope Valley from 11 a.m. Sunday to 9 p.m. Wednesday, and in the Santa Clarita Valley from Monday morning through Wednesday night.

“The very high temperatures create a dangerous situation in which heat- related illnesses are possible,” warned an NWS statement, urging area residents to avoid working in the sun and to take frequent rest breaks. And “never, ever leave people or pets in enclosed vehicles, even for a short period of time.”

Officials at the South Coast Air Quality Management District, meanwhile, said that ozone, a lung-damaging component of smog, would reach particularly unhealthy levels in the Santa Clarita, San Fernando and San Gabriel valleys, Inland Empire and the San Bernardino and San Gabriel mountains.

It said scorching temperatures will combine with atmospheric inversions, which trap pollution near the ground, to cause persistently poor air quality at least through early next week.

Southern California has experienced an increase in bad air days following decades of improving air quality, the Los Angeles Times reported. Last year the region experienced its worst smog season in years, logging 132 bad air days and ozone concentrations not seen since 2009.