High heat and fire danger loom for California ahead of Fourth of July weekend

Much of California faces a one-two weather punch this week as a dangerous heat wave and high fire risk loom at a time when millions will be outside celebrating Independence Day.

Temperatures in the Sacramento Valley could reach 115 degrees, according to Kate Forrest, a meteorologist with the National Weather Service in California’s capital city. A heat warning in the area will begin Tuesday and is expected to last until at least Saturday.

“We are expecting elevated heat and extreme heat risk throughout most of interior California,” Forrest said. “This heat is going to be a prolonged event.”

Forecasters expect the heat wave to start Tuesday in inland California and then broaden into the Pacific Northwest and deeper into Southern California later in the week. Excessive heat watches, warnings and advisories will blanket the West on Tuesday from southern Oregon to the low desert in southeast California, according to the National Weather Service.

The elevated temperatures are the result of a strong high pressure system that will linger over the region.

“High pressure systems force air downward, causing that air to compress and increase temperature,” Forrest said. “That air stays stagnant.”

State officials are preparing for the heat. Gov. Gavin Newsom directed emergency officials to activate the state’s operations center — its central command station during emergencies — his office said in a news release.

The hot weather could stay above 80 degrees F even at night in some places. By Friday, most of inland California will face “extreme” conditions, according to the HeatRisk map, a tool from the Centers for Disease Control and Prevention and the National Weather Service. The designation means the agencies expect impacts on health care facilities and infrastructure.

The area around Medford, Oregon, and other southern parts of the state are under an excessive heat watch through Saturday, as well.

“If you have neighbors who don’t have air conditioning, check on them a little more often,” said Brad Schaaf, a lead meteorologist at the National Weather Service in Medford.

Some forecast models suggest the Medford region could set a record for the number of consecutive 100-degree days, Schaaf said. The region endured 10 such days in a row in 1967.

Dangerous fire conditions will accompany the sharp rise in temperatures Tuesday in both states.

Pacific Gas & Electric said Monday that power shut-offs are likely in 10 California counties Tuesday, given the high winds and dry conditions expected throughout central California. Shut-offs are designed to proactively reduce the risk of wildfires in areas where winds could topple power lines or cause trees to fall on them. Some shut-offs are expected Wednesday, too.

But those preventive outages are likely to leave some communities without electricity as the mercury rises to dangerous levels.

Forrest predicted up to a 45% chance of wind gusts over 35 mph in the Sacramento Valley area, with humidity levels that could drop into the single digits — a recipe for fast-moving wildfires.

Plants are dry and ready to burn, particularly at elevations below 3,000 feet, she added.

“If ignition starts, it will spread,” Forrest said.

That’s tough timing as July Fourth celebrations kick off with fireworks displays.

“It’s not ideal,” Schaaf said. “We want to urge everyone to use extreme caution when participating in activities that cause sparks, like using fireworks.”

The California Department of Forestry and Fire Protection is tracking 13 active fire incidents, only four of which have burned more than 100 acres.

In the Southwest, wildfire season has already turned deadly. Two people were killed and 500 homes were destroyed in a wildfire that ravaged the community of Ruidoso, New Mexico, last month.

Climate change increases the likelihood of fire weather and heat waves. Last year, the nonprofit group Climate Central calculated how the number of fire weather days had shifted across the U.S. from 1973 to 2022. The analysis found that the Sacramento Valley faces nearly two more weeks of fire weather, on average, than it did 50 years ago.

Heat waves, meanwhile, are occurring more frequently and lasting longer, according to data from the U.S. Environmental Protection Agency. U.S. cities, on average, used to experience two heat waves per year; now, they typically get six. Those heat waves last about a day longer, too, the data suggests.

Evan Bush

Evan Bush is a science reporter for NBC News. He can be reached at [email protected].