Heat wave expected

Long-duration heat wave expected to bring dangerous conditions to California

By Amy Graff

A heat wave that’s being called “anomalous” and “potentially dangerous” by the National Weather Service is expected to bring sizzling temperatures and a high risk of wildfires in California starting Tuesday and continuing for several days, including over the July Fourth holiday.

“This level of heat could pose a danger to the public if proper heat safety is not followed,” the agency wrote in its forecast.

The most notable factor that is expected to contribute to the severity of this event is its long duration, UCLA climate scientist Daniel Swain said in his heat wave forecast broadcast over YouTube on Monday.

“This is not going to be a couple of days where it’s really hot, and then the sea breeze kicks in, and it’s cooler,” Swain said. “This could last for a full week at peak intensity in some places, and perhaps even longer. Across some parts of the northern interior part of California, it may continue, essentially, through mid-July. … Today is July 1. That would be 10-plus days from now. So this is a this is a pretty big-deal event.”

Case in point: Redding, which sits on the top of the Sacramento Valley, is forecast to see temperatures over 110 degrees over at least nine days, with a peak temperature of 117 degrees expected Friday, according to the weather service.

While some locations are unlikely to break all-time record highs in this event, Swain said it’s more likely that several spots could see records broken in terms of duration of afternoon high temperatures in excess of, say, 100 degrees, even 110 degrees. 

The exceptional heat that could break daily records across multiple days is expected across inland portions of the state in an area stretching from the lower deserts of Southern California to the Antelope Valley, across the San Joaquin Valley, through the Sacramento Valley and the coastal mountains ringing it, and into the Sierra foothills, Swain said. 

Coastal areas — locations directly on the ocean and about 20 miles inland from it — are expected to be spared the extreme heat. Downtown San Francisco is forecast to see the peak of the heat wave Wednesday, with a high of 86, and Los Angeles is predicted to record the highest temperature of the event Friday, with a reading of 91, according to the weather service.

“This is not going to be the kind of heat wave that brings 105-degree temperatures to the beaches in San Francisco or LA,” Swain said. “That’s a different kind of heat wave — and that very likely will not happen with this one. So we’re not talking about, you know, downtown San Francisco seeing an all-time record high or anything like that. It should be much warmer than average and actually quite warm to even hot, even along the immediate coast for a few days. It will be notably warm with an absence of a marine layer, but the real problem is going to be across inland areas.” 

While the daytime highs in inland areas are going to be attention-grabbing, the overnight lows could be more concerning in many areas, especially in the Central Valley and the foothills ringing the valley. “In places that could see temperatures of 100 to 110-plus for a very long duration, overnight minimum temperatures might not drop below 70 degrees in many of these places, and in some parts of the foothills not below 80 degrees,” Swain said. “So we may actually see 150 to 170 consecutive hours of temperatures above 80 to 85 degrees in the foothills during this event. It just isn’t going to cool off, even at night.”

With the heat wave looming, the weather service has been issuing a series of excessive heat watches and more excessive heat warnings. The agency is advising people to stay hydrated, to avoid being outside in the middle of the day and to seek out air conditioning. The heat wave is expected to increase the risk of wildfires across the state, and several red flag warnings have also been issued. “Outdoor burning is not recommended,” in areas under the warnings, the agency said.