Early heat wave to break records across California and Southwest

In California and the Southwest, a long-lasting early-season heat wave is expected to send temperatures skyrocketing this week.

It feels like summertime in March across much of the western United States this week, as an extraordinary, early heat wave sends temperatures skyrocketing in California and the Southwest.

Highs above 90 degrees Fahrenheit are expected to be widespread in Southern California, with parts of Arizona and Nevada reaching the triple digits. Some 39 million people in the region are under heat alerts Monday, and the heat wave is likely to expand and intensify as the week goes on.

The National Weather Service said the “anomalously early” heat wave is caused by an unusual pattern in which a dome of high pressure builds and settles over the West, baking the region in sweltering conditions.

“Daily record-tying/breaking highs will become more common across southern California, the Desert Southwest and into the Great Basin over the next couple of days,” the agency said Monday in its short-term forecast. “These temperatures will serve as a baseline for even more anomalous, more widespread record-breaking heat expected later this week.”

In Los Angeles, highs were forecast to be in the mid- to high-90s all week, with an expected peak Thursday of 98 degrees. Temperatures in Phoenix should climb into the triple digits by Wednesday, with Thursday expected to reach 105. Multiple cities in southern Nevada, meanwhile, may climb to 107 by later this week — blisteringly hot conditions for this early in the year.