Fire danger escalating in Northern California as McKinney blaze erupts

“There’s definitely concern anytime you have a heat wave followed by lightning, especially in midsummer in the Western U.S.,” said Nick Nauslar, a fire meteorologist with the National Interagency Fire Center. “We think that we’ll see ignitions and potentially a number of significant fires as well.”

In an ominous sign of conditions on the ground, a new wildfire — the McKinney Fire — is spreading rapidly near the California-Oregon border after an initial bout of thunderstorms Friday. It grew explosively Friday night and Saturday with extreme fire behavior, forming a towering pyrocumulonimbus cloud, or a fire-generated thunderstorm. Radar detected lightning unleashed by the storm.

Incredibly, the fire had already grown to 30,000 to 40,000 acres by Saturday afternoon, according to the Klamath National Forest.

Mandatory evacuation orders have been issued for a broad area around the fire, and two smaller fires are also burning nearby.

There are concerns that the fire could continue spread rapidly amid the hot, dry conditions near a zone with no recent fire history, meaning there is a large amount of fuel (dried-out and dead vegetation) that could be ignited.

The National Weather Service in Medford, Ore., issued a red flag warning for high fire danger in the area Saturday and, on Saturday evening, extended the warning into Sunday afternoon.

“Lightning and high fire danger will likely result in new fire starts. Gusty thunderstorm winds could contribute to fire spread,” it wrote. “Despite rainfall, initial attack resources could be overwhelmed and holdover fires are possible.”

The region has been roasting the past week under a heat dome, a ridge of high pressure in the upper atmosphere. The dome has been forecast to weaken and move eastward over the weekend and into next week, allowing a brief intrusion of moisture from the Southwest monsoon. Meanwhile, an approaching trough, or dip in the jet stream, will usher in winds and lower temperatures, and act as a trigger for more organized thunderstorms.

Under this setup, storms may move so quickly that they’ll drop very little rain at a given location, increasing the chances that lightning ignites vegetation in the parched landscape.

“It’s a classic 1-2 critical fire weather punch with a preceding extended and intense heat wave followed by the breakdown of the ridge,” said Brent Wachter, a fire meteorologist with the Northern California Geographic Coordination Center in Redding, Calif., in an email. “Break-downs in an especially impactful heat wave event usually lead to large fires due to either multiple lightning ignitions … with strong storm wind outflows and/or increasing straight line wind.”

Although the California fire season so far has not been nearly as extreme as in the previous two years, that could change quickly, as it did after the August 2020 lightning siege in Northern California. That year brought a modern record of 4.3 million acres burned in the state.

Given long-term severe to extreme drought, this week’s soaring temperatures have left a swath of the West primed to burn, as shown in a map of the Energy Release Component, a metric that indicates vegetation flammability.

“Generally speaking, places that experience ERC values above their local 95th percentile are increasingly prone to have an ignition that escapes initial fire suppression efforts and becomes a big fire,” said John Abatzoglou, a climatologist at the University of California at Merced, in an email. “Notably, this becomes an even bigger problem when a large geographic area is simultaneously experiencing high fire potential and/or there are numerous large fire events active that drain from existing fire suppression resources.”

According to Abatzoglou, heat waves can ratchet up the fire season, particularly heat waves that are long-lasting.

Heat has been building across interior California in recent weeks and probably had a hand in the spread of the Oak Fire outside Yosemite National Park. That fire grew explosively without much wind amid dense, record-dry vegetation. The fire has destroyed 109 single residential structures as of Saturday and is 52 percent contained.

“While June was a bit of a quiet month and we largely avoided persistent heat, things have changed over the past 3 weeks,” Abatzoglou wrote, noting that Fresno, Calif., could experience its second-longest streak of days over 100 degrees Fahrenheit by next week.

Scores of record highs for July 29 were set Friday in interior parts of Northern California and the Pacific Northwest, with temperatures ranging from 100 to 115 degrees. Some places neared all-time highs — or the highest temperature on record for any month. Mount Shasta, Calif., soared to 106 degrees, just one degree short of its all-time high, and Medford reached 114, also one degree from its all-time high.

A study recently published in the Journal of Climate, on which Abatzoglou is a co-author, found that large fires in North America are seven times more likely to start during persistent summer heat waves. Numerous studies have linked increasingly frequent and intense heat waves, as well as increases in wildfire activity and burned area, to human-caused climate change.

Even with a cool-down expected next week, fire danger is forecast to remain high in the state during August, and fierce autumn “offshore” winds can arrive as early as September.

“This will mean that the door will be open for ignitions to become problematic fires,” Abatzoglou wrote. “Widespread dry lightning … as well as wind events are certainly things to look out for as they have the potential to dramatically alter the course of the 2022 fire season should they materialize.”

Jason Samenow contributed to this report.