A monster heat wave descended on Southern California on Sunday, bringing triple-digit temperatures across a large swath of the region and fueling dangerous fires in Silver Lake and San Diego County.

The Border Fire east of San Diego had burned 1,500 acres, and officials were evacuating the town of Potrero.

As of noon, numerous areas had exceeded 100 degrees, including Burbank, Beverly Hills, Woodland Hills, Fullerton, Glendale and Riverside.

The 106-degree reading in Burbank set a new record for the day and Woodland Hills tied its record. One National Weather Service weather site showed a 112-degree reading in Beverly Hills.

In Silver Lake, a fire quickly spread to brush along the 2 Freeway, prompting firefighters to call for more resources and air support. The freeway was closed in both directions near its terminus in Echo Park.

Map shows the approximate location of the freeway closure. (Los Angeles Times)

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Los Angeles Fire Department choppers made water drops on a neighborhood along the freeway, and firefighters were working in backyards with hoses trying to prevent structure losses.

In the end, about 5 acres of brush burned and two homes were damaged, according to the LAFD. About 20 homes were threatened.

Temperatures are expected to rise Monday, the first day of summer, in the heat wave forecast to last through Tuesday.

As the heat wave taxes California's power supply, regulators announced a Flex Alert in Southern California for Monday, urging residents and businesses to conserve power.

The California Independent System Operator said the alert will be in effect from 10 a.m. to 9 p.m. Monday. The biggest concern will be Monday afternoon, when air conditions will be at peak use.

"Consumers can help avoid power outages by turning off all unnecessary lights, using major appliances after 9 p.m. and setting air conditioners to 78 degrees or higher. During times of high temperatures, demand on the power grid can be strained, as air conditioner use increases," Cal ISO said in a statement.

The conservation alert is voluntary.

The National Weather Service issued a red flag fire warning for large parts of the region because of extreme heat, low humidity and the potential for gusty winds. The Sherpa fire in Santa Barbara County has already burned more than 7,800 acres, and firefighters have also been dealing with smaller blazes.

Forecasters said there was “potential for extreme fire behavior/rapid fire spread” of the Sherpa fire because of continued sundowner winds and hot temperatures.

As of Sunday evening, the San Diego County fire was growing quickly.

The fire ignited in brush amid rocky, steep terrain near state Route 188 and state Route 94 about 11:30 a.m., Capt. Kendal Bortisser of the California Department of Forestry and Fire Protection said. Flames later jumped Route 94 and threatened about 25 homes along Emery Road and Plaskon Lane.

Emery is just east of Route 188. Plaskon is east of Emery and north of Route 94. An evacuation center has been set up at the Campo Community Center at 300 Sheridan Road, Bortisser said.

More than 100 firefighters were battling the blaze in 104-degree heat with 10% humidity, authorities said. If the blaze continues on its path, it may threaten 50 more homes within the hour, Bortisser said about 2 p.m. He didn't say where those homes were located.

Route 94 is currently closed between Route 188 and Potrero Valley Road.

As temperatures ticked above 100 degrees Sunday afternoon, Valerie and Richard Gonzalez left Target in Alhambra with a cart laden with two large tower fans and some beer.

As Richard Gonzalez pushed the cart to the car, he shared his strategy for dealing with beers that warmed too quickly in the sun. “Drink them in two gulps," he said. There's no air conditioning at their home in El Sereno, so they plan to set up a pool, blast the fans and put the beers on ice to stay cool.

"We're just going to hang out and wait for the sun to go down," Valerie Gonzalez said. When they got inside their car, it was so hot that Valerie sent her husband back to Target for a towel with which to wrap the steering wheel. "We're going to be suffering some third-degree burns from these leather seats," Valerie said.

At neighborhood favorite Fosselman's Ice Cream down the street, customers left the venues outside empty and crammed into the parlor's refrigerated interior to enjoy their ice cream with air conditioning. For Bryan Adams and Katia Kaplun, the year's hottest day began with a stop at the Splash Pad in City Terrace Park, where their young son could run through jets of water.

After that came a stop at Fosselman's for ice cream, then back to the house to cool down some more. Their house isn't well shaded and doesn’t have central air conditioning, but wall-mounted units, outdoor fans and a kiddie pool should help, Adams said.

"We live a lot of the year outside here in Southern California, so we have to be creative about ways to stay cool," Adams said.

Juan Ortiz and Marianella Villa got out of their car, ordered a scoop of strawberry each, and got back in the cars to eat it with cold air blasting. "It's just too hot today," Villa said. "It's supposed to be hotter tomorrow," Ortiz added. "Maybe we'll be back here again!"

What are the health and safety concerns?

Heatstroke is possible, the weather service said, especially among those who plan on spending Monday outdoors or people without access to air conditioning.

Forecasters warned against leaving people or pets in enclosed vehicles — even for a short period of time.

Power outages are possible as well, the weather service said.

Other agencies have also issued warnings heat. The Occupational Safety and Health Administration recommended frequent breaks in shaded or air-conditioned areas.

The Los Angeles County Public Health Department said it plans to issue a heat alert Sunday through Tuesday, when temperatures are expected to start to decline.

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Why is this heat wave occurring?

The blistering heat is the result of an upper-level ridge of high pressure that is building slowly over Southern California. Sirard said the system should start to weaken by Tuesday and temperatures should start to drop.

Lyndsay Winkley of the San Diego Union Tribune contributed to this report.

frank.shyong@latimes.com

ruben.vives@latimes.com

kate.mather@latimes.com

sarah.parvini@latimes.com

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UPDATES:

7:24 p.m.: Updates to the Border fire size.

4:33 p.m.: Updated throughout with new information.

2:26 p.m.: Updated with additional information on the fire.

June 19, 1:55 p.m.: This article was updated with temperature updates and information about a fire and freeway closure.

10:50 a.m.: This post was updated with new numbers for the Sherpa Fire.

8:50 a.m.: This post was updated with a new forecast, additional questions and graphics.

This post was originally published at 6:06 p.m. June 18.