The Southland’s fiercest heat wave this year continued baking the area Monday, threatening “excessive heat” and elevated fire danger into next week, while again raising the potential of rolling power blackouts due to excessive electricity demand.

The high heat can be attributed to a strong ridge of high pressure anchored over Nevada, said NWS meteorologist Dave Bruno.

An excessive heat warning, which has been extended since it was first issued last week, will be in force until 9 p.m. Thursday in the San Fernando, Santa Clarita, San Gabriel and Antelope valleys, as well as the San Gabriel and Santa Monica mountains. The weather service said conditions in those areas would be “dangerously hot.” In inland Orange County and the Santa Ana Mountains, the warning will expire at 10 p.m. Thursday.

A less serious heat advisory will be in effect until 9 p.m. Thursday in the L.A. coastal zone — beach cities, metropolitan Los Angeles, Downtown L.A. and the Hollywood Hills.

“Very hot conditions will continue through the week with very warm nights, especially for valley and interior areas,” according to the NWS. “Temperatures will cool only slightly later in the week and will remain above normal through early next week. There is a slight chance of thunderstorms through Wednesday mostly over the mountains and the Antelope Valley.”

Monday afternoon, the NWS reported temperature records for the date in Lancaster, which reached 110 degrees, and Palmdale, which reached 111.

Along with torrid weather, the NWS forecast “elevated fire danger.” The NWS has not issued any red flag warnings because winds have not been strong enough to meet NWS criteria, Bruno said.

But “it’s not going to take much” to set a wildfire in addition to those already burning, he said, and red flag warnings may yet be issued, particularly in the event of more dry lightning.

The NWS noted that some coastal areas on Monday saw significantly decreased temperatures — “in some cases by as much as 15-20 degrees” — in the morning and early afternoon hours thanks to lingering low clouds.

But that relief wasn’t expected to last, with Tuesday expected to be hot again.

“The high does start to weaken Wednesday and Thursday but not significantly enough to provide all that much relief,” according to the NWS. “It will likely take until Friday or perhaps not until Saturday before high temps drop below advisory/warning levels.”

The excessive heat has led to stress on the state’s electrical grid over the past few days, prompting some rolling blackouts Friday night. Utility companies warned customers Monday that more such power interruptions are possible in peak afternoon hours during the heat wave. Flex Alerts urging customers across the state to conserve energy will be in effect each afternoon and evening through Wednesday.

“Extreme heat will significantly increase the potential for heat related illnesses, particularly for those working or participating in outdoor activities,” according to he NWS. “Take extra precautions if you work or spend time outside. When possible reschedule strenuous activities to early morning or evening.”

Also confronting Southland residents is foul air as a result of “the current heat wave, along with stagnant weather and ongoing wildfires,” according to the South Coast Air Quality Management District.

Smoke advisories were issued as a result of the Ranch 2 Fire north of Azusa and Duarte, and the Lake Fire northeast of Castaic.

The AQMD urged people “who smell smoke or see ash to limit exposure by remaining indoors with windows and doors closed or to seek alternate shelter and avoid vigorous physical activity.”

The heat wave, which Bruno said is the fourth this summer, is the longest so far, he said, adding that Tuesday’s temperatures should be as high as Saturday’s. Some cooling will begin Thursday, but temperatures will not revert to normal before the middle of next week, he said.

Off the coast, a small craft advisory issued because of an expectation of hazardous conditions will be in force through 3 p.m. Tuesday, and a gale watch will be in effect from Tuesday afternoon through late Wednesday night amid winds of 20-30 knots, gusting to 35 knots.

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