Excessive heat warnings go into effect Wednesday for a widespread part of Southern California as the region prepares for some of the warmest temperatures of the year.
The unrelenting blast of late-summer heat, including triple-digit temperatures, triggered calls for power conservation, elevated concerns about wildfire dangers, and heat and air quality advisories.
Here's what to know about the August heat wave.
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How long with the extreme heat last?
Excessive heat warnings go into effect on Wednesday for all areas inland of the beaches. Those warnings will remain in effect through Monday, but the heat risk continues through Tuesday and possibly longer as the high-pressure system weakens.
"We're halfway through the week, but this heat wave is just getting started," said NBC4 forecaster Belen De Leon.
Temperatures Wednesday will run about 10 degrees warmer than Tuesday.
When will the heat wave peak?
The hottest temperatures are expected Sunday and Monday. Widespread triple-digit heat will blanket valleys and inland areas. Some valley areas are likely to approach all-time records.
"If you think (Wednesday) is hot, the weather over the holiday weekend is going to get even hotter," said De Leon.
How hot will it be around Southern California?
In Los Angeles County, an excessive heat warning that will be in effect from 11 a.m. Wednesday to 8 p.m. Monday for the Antelope Valley, Los Angeles County mountains, Santa Monica Mountains, the coastal region and the San Fernando and San Gabriel valleys.
The Antelope Valley could see temperatures as high as 113 degrees. Other valley areas could hit 112 and the mountains and inland coastal areas could reach 105.
In Orange County, an excessive heat warning took effect at 10 a.m. Tuesday and will continue through 8 p.m. Monday for coastal and inland areas and the Santa Ana Mountains and foothills. OC beaches will be in the 80s, with inland areas hitting the 90s, and possibly up to 105 farther from the coast in cities such as Anaheim, Garden Grove, Irvine and Fullerton.
Farther inland, an excessive heat warning has been issued until 8 p.m. Monday with dangerously hot conditions in the forecast and temperatures expected to reach between 105 and 112 in parts of Riverside County. The heat warning is in effect for the Riverside County valleys and Inland Empire, Riverside, Ontario, Moreno Valley, Rancho Cucamonga and Corona.
Will temperatures cool overnight?
Unfortunately, evenings and overnights will offer little relief. Lows will stay in the 70s and even in the low 80s in some of the hotter areas.
"It's going to take a while for these temperatures to come down, even after the sun has set," De Leon said.
What about California's power situation?
The California Independent System Operator, which manages the state's power grid, noted that it has already issued a Restricted Maintenance Operations order that will take effect Wednesday and continue through next Tuesday. The order limits maintenance operations between noon and 10 p.m. each day to ensure all power systems remain in service.
Cal-ISO warned that it may be issuing Flex Alerts. The alert is a request for voluntary power conservation during peak hours, generally between 4 and 9 p.m.
How is the air quality in Southern California?
An ozone advisory was issued for the region. The ozone advisory will be in effect from 11 a.m. Tuesday to Sunday. Unhealthy for Sensitive Groups and Unhealthy Air Quality Index (AQI) levels are likely in inland areas of the South Coast Air Basin most afternoons. Air quality will likely be even worse in the San Bernardino Mountains and San Bernardino Valley with Very Unhealthy AQI levels possible in the afternoon.
You can check the South Coast air quality map or click here for current air quality conditions by region. You also can sign up for air quality updates and notifications from the South Coast AQMD app.
