Excessive Heat Expected in California With Arrival of Heat Dome

Severe heat is expected to bake parts of the United States from Texas to California starting on Tuesday, with temperatures soaring to the triple digits, according to the National Weather Service.

Here are some key things to know:

• Parts of California could experience temperatures 20 degrees higher than typical for early June, forecasters said. Temperatures in parts of the state could reach as high as 110 degrees.

• Parts of Texas were expected to see above-average temperatures, from Austin through the area south of San Antonio near the Rio Grande.

• By Thursday, Phoenix was expected to have 110-degree temperatures for the first time this season.

Here’s what to expect in the affected areas:

In California, areas from outside Los Angeles to Redding, more than 500 miles north, were set to be under an excessive heat watch from as early as Tuesday morning through Thursday evening, forecasters said. Abnormally high temperatures were also expected in the San Francisco Bay Area.

The National Weather Service in Hanford, Calif., in the Central Valley, warned of “dangerously hot conditions” in the region, where farmers grow a big share of the United States’ fruit, vegetables and nuts. The extreme heat is expected to last through Thursday night.

Forecasters cautioned against leaving children and pets in cars, noting that “car interiors will reach lethal temperatures in a matter of minutes.”

“Extreme heat is an invisible but dangerous consequence of climate change, and California’s outdoor workers, seniors and children are particularly vulnerable,” the California Environmental Protection Agency said on social media.

Health officials urged people to stay indoors in air-conditioned spaces, and to drink plenty of water.

In an advisory to employers on Monday, the California Division of Occupational Safety and Health said that temperatures were forecast to peak on Wednesday with readings of 106 degrees in Redding, 104 in Chico and 103 in Fresno.

Amy Palmer, a spokeswoman for California’s Office of Emergency Services, said on Saturday that Gov. Gavin Newsom’s office was “actively watching the heat expected” with plans to “step up outreach for people who don’t have easy access to hydration and air-conditioning.”

A heat advisory was issued for parts of Texas near the Mexico border beginning Monday afternoon, with heat indexes of 110 to 114 degrees. Similar advisories were expected through Thursday, the National Weather Service’s Austin/San Antonio branch said.

Phoenix was expected to have 110-degree temperatures this week for the first time this season after experiencing that level of heat more than 50 times last year. That record-breaking heat resulted in the deaths of 645 people in the city and surrounding Maricopa County, according to the county Public Health Department.

In the wake of the disastrous heat, the Maricopa Association of Governments, a regional planning agency, published a guide to a network of public, air-conditioned buildings known as cooling and respite centers on a map that also shows the locations of drinking water fountains.

The extreme heat has already afflicted Mexico.

Emergency officials are watching for what forecasters call a ridge — an elongated area of relatively high atmospheric pressure — to push hot weather north from Mexico.

The temperatures may then settle for a few days in a heat dome, which occurs when atmospheric conditions act like a lid on a pot, preventing precipitation and the release of hot air.

In Mexico, high temperatures caused power outages and drought, and killed at least 48 people, according to the country’s health ministry.

Howler monkeys have fallen dead from trees because of the heat. In the coming weeks, the country is bracing for what forecasters at the National Autonomous University of Mexico expect will be “the highest temperatures ever recorded.”

Jorge Zavala Hidalgo, director of the university’s Institute of Atmospheric Science and Climate Change, said researchers forecast temperatures from 95 degrees in the capital, Mexico City — a temperate climate where few of the 21 million people have air-conditioning at home — to 115 degrees in San Luis Potosí, a mountainous city in Central Mexico.

The heat onslaught is in line with the summer outlook from the National Oceanic and Atmospheric Administration, which predicted the likelihood of above-average temperatures for June through August across the West and Southwest.

Amanda Holpuch contributed reporting.