UPDATE: Phoenix and Tucson tie heat records for the date
The Latest on the heat wave affecting the Southwestern U.S. (all times local):
Phoenix posted a high of 118 degrees on Monday, tying the record for the date set last year.
National Weather Service meteorologists say it's the fifth hottest day in Phoenix since records have been kept.
Tucson tied a record with a high of 115 degrees Monday.
It's the third-highest temperatures ever recorded at Tucson International Airport.
The all-time high for Tucson is 117 degrees, set on June 26, 1990. That's the same day Phoenix saw its all-time high of 122 degrees.
Los Angeles is extending the hours of a dozen cooling centers around the city due to the West's increasing heat wave.
Mayor Eric Garcetti's office says the centers where people without air conditioning can seek relief will operate until 10 p.m. on Tuesday and Wednesday.
A regional heat advisory issued by the National Weather Service will be in effect from 11 a.m. Tuesday to 9 p.m. Wednesday. Temperatures in the San Fernando Valley will surpass the century mark during the period.
The operators of California's power grid have also issued a "Flex Alert" that calls for electricity conservation both days, urging residents to shift demand to after 9 p.m.
Firefighters are battling a grass fire in the hills near a Northern California town that has sent a plume of dark smoke up to the sky and prompted voluntary evacuations.
Contra Costa County fire officials say the blaze started Monday afternoon behind Campolindo High School in Moraga.
The grass fire is threatening homes, but no evacuations have been ordered.
Officials say they have issued a shelter-in-place order while fire crews try to control the 10-acre (4-hectare) blaze with help from two helicopters dumping water from the air.
Many Bay Area cities shattered heat records on Sunday as a heat wave arrived over the weekend in the Southwestern U.S.
Border Patrol agents in the Tucson Sector reportedly stopped two human smuggling attempts at the Arizona border with three men from Mexico found locked in the trunks of vehicles in 100-degee conditions.
They say two men were freed from the trunk of a vehicle Saturday evening near Benson and were drenched in sweat.
Border Patrol officials say a second smuggling attempt was thwarted Sunday evening when agents at an immigration checkpoint near Whetstone referred two Tucson women in a car for a secondary inspection.
During the inspection, agents found one Mexican man concealed in the trunk.
In both cases, they say the men being smuggled didn't know how to escape from the trunk in case of an emergency.
The three men were arrested on charges of immigration violations along with four U.S. citizens in the vehicles for suspicion of human smuggling.
The National Weather Service is warning those hiking or sightseeing in southern Utah's red rock deserts and parks this week that temperatures could reach dangerously high levels.
Forecasters issued an excessive heat warning for southern Utah's Zion National Park, Glen Canyon National Recreation Area and Lake Powell through Thursday night. Temperatures could reach 115 degrees in some areas.
The Weather Service also warns that temperatures will be very hot this week throughout southeastern Utah, including in Canyonlands National Park, Moab, Blanding, Kanab and Grand Staircase-Escalante National Monument.
Temperatures elsewhere around Utah are expected on Tuesday to tie or break record highs previously set for June 20.
American Airlines has cancelled 38 flights in and out of Phoenix on Tuesday afternoon because of extreme heat.
The cancellations are for operations by smaller regional jets that have lower maximum operating temperatures than full-size airliners. Those jets can't operate when it's 118 degrees or above.
American warned passengers over the weekend that it may have to ground flights during a heat wave that could send the temperature soaring to near 120 degrees. Spokesman Ross Feinstein says the late afternoons are the peak affected times.
The airline is letting Phoenix passengers flying during the peak heat Monday through Wednesday to change flights without a fee. The forecast calls for a high of 119 Tuesday.
Extreme heat creates changes in air density that makes it harder for airplanes to take off.
Surgeons at the major burn center serving Arizona are urging people to be aware of the danger of severe burns caused by excessive heat blanketing the southwestern United States.
Dr. Kevin Foster of the Arizona Burn Center in Phoenix issued the warning Monday.
He says second and third degree burns from hot asphalt and concrete, playground equipment, car and truck interiors and scalding water from outdoor hoses are common when temperatures exceed 100 degrees.
Temperatures in parts of Arizona, Nevada, and California are expected to top 115 degrees this week.
Foster says young children are particularly vulnerable because their skin is more sensitive.
The warning also applies to pets.
First aid for burns involves pouring cool water over the area for several minutes and seeking medical attention.
Tourists hitting the Las Vegas Strip will feel the sizzle Monday as temperatures could top 114 degrees.
Meteorologist Ashley Allen with The National Weather Service in Las Vegas says the city's airport is forecast to hit 114 on Monday, but temperatures on the Strip could reach somewhere between 115 and 120 degrees.
Allen says the Las Vegas Strip's tall, close buildings and long stretches of concrete cause the area to heat quickly and cool slowly. She says it's hard to predict exactly how hot the Strip will get because the Weather Service does not get official readings there.
The Las Vegas-area is forecast on Tuesday to tie a record high of 117 degrees, last recorded in 2013.
An excessive heat warning is in effect as temperatures are expected to stay above 110 degrees into the weekend.
The National Park Service is warning visitors to Arizona not to hike into the Grand Canyon because of excessive heat.
Temperatures below the rim of the canyon are expected to reach as high as 117 degrees this week. Temperatures on the rim are expected to be in the low to high 90s.
If hikers do decide to go ahead with their planned trips, the Park Service says they should take extra precautions to avoid being overcome by the excessive heat. That includes hiking only before 10 a.m. and after 4 p.m. to avoid strenuous exertion during the hottest part of the day. Drinking extra water and sports drinks will help prevent dehydration that can trigger a health crisis like a heat stroke.
American Airlines is warning passengers that it may have to ground flights in Phoenix during a heat wave that could send the temperature soaring to 120 degrees.
The airline is letting Phoenix passengers flying during the peak heat Monday through Wednesday to change flights without a fee. The forecast calls for a high of 118 on Monday and 120 on Tuesday in Phoenix.
The heat will have the biggest impact on smaller regional jets flying out of Phoenix.
Extreme heat creates changes in the air density that make it harder for airplanes to take off. Airlines respond by imposing weight restrictions, such as carrying less cargo and fuel. But in some cases, they will ground flights during the peak heat.