“There’s definitely a concern any time you have a heat wave followed by lightning, especially in midsummer in the western United States,” said Nick Nauslar, fire meteorologist at the National Interagency Fire Center. “We think we will see some ignitions and potentially a number of large fires as well.”
In a worrying sign of conditions on the ground, a new wildfire – the McKinney Fire – is rapidly spreading near the California-Oregon border after an initial bout of thunderstorms on Friday. It grew explosively Friday night and Saturday with extreme fire behavior, forming a towering pyrocumulonimbus cloud, or a thunderstorm generated by fire. Radar lightning detected tossed about by the storm.
Incredibly, the fire had already reached 30,000 to 40,000 acres by Saturday afternoon, according to the Klamath National Forest.
Mandatory evacuation orders have been issued for a large area around the fire, with two small fires also burning nearby.
The fire is feared to continue to spread rapidly in hot and dry conditions near an area no recent fire historywhich means there is a lot of fuel (dry, dead vegetation) that could ignite.
The #McKinneyFire in far northern California is displaying unusually extreme and erratic fire behavior this evening, producing a pyrocumulonimbus plume nearly 50,000 feet (!!) as it spreads rapidly.
— US StormWatch (@US_Stormwatch) July 30, 2022
The National Weather Service in Medford, Oregon, issued a red flag warning for high fire danger in the area on Saturday and, on Saturday evening, extended the warning until Sunday afternoon.
“Lightning and high fire danger will likely lead to new fire starts. Gusty storm winds could help spread the fire,” he writes. “Despite precipitation, initial attack resources could be exceeded and persistent fires are possible.”
The region toasted last week under a heat dome, a ridge of high pressure in the upper atmosphere. The dome is expected to weaken and move eastward over the weekend and into next week, allowing for a brief intrusion of southwest monsoon moisture. Meanwhile, an approaching trough, or dip in the jet stream, will usher in lower winds and temperatures, and act as a trigger for more organized thunderstorms.
In this configuration, storms can move so quickly that they will drop very little rain in any given location, increasing the chances of lightning igniting vegetation in the parched landscape.
“This is a classic 1-2 critical fire weather punch with a previous prolonged and intense heat wave followed by ridge collapse,” said Brent Wachter, fire meteorologist at Northern California Geographic Coordination Center in Redding, Calif., in an email. “Outages during a particularly hard-hitting heat wave event typically result in large fires due to multiple lightning ignitions…with strong storm wind outflows and/or increased straight-line winds.”
Although California’s fire season so far has not been as extreme as it has been in the previous two years, that could change quickly, as it did after the August 2020 lightning siege in the northern California. That year, a modern record 4.3 million acres were burned in the state.
Given the long-term severe to extreme drought, soaring temperatures this week have left parts of the West primed to burn, as shown in a map of the Energy Release Component, a metric that indicates the flammability of vegetation.
“Generally speaking, locations that experience ERC values above their local 95th percentile are increasingly likely to have an ignition that escapes initial fire suppression efforts and becomes a large fire,” said John Abatzoglou, a climatologist at the University of California, 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 many large active fires that drain existing fire suppression resources.”
According to Abatzoglou, heat waves can speed up the fire season, especially long-lasting heat waves.
Heat has been building up in the California interior in recent weeks and likely played a role in spreading the Oak Fire outside of Yosemite National Park. This fire developed explosively without too much wind in the middle of dense and dry vegetation. The blaze destroyed 109 individual residential structures on Saturday and is 52% contained.
“While June was a somewhat quiet month and we largely avoided lingering heat, things have changed over the past 3 weeks,” Abatzoglou wrote, noting that Fresno, Calif., may be experiencing its second longest sequence of days over 100 degrees Fahrenheit. by next week.
Dozens of records for July 29 were set Friday in the interior regions of northern California and the Pacific Northwest, with temperatures ranging from 100 to 115 degrees. Some places have approached historic highs – or the highest temperature on record for a month. Mount Shasta in California soared to 106 degrees, just one degree off its all-time high, and Medford soared to 114, also one degree off its all-time high.
A study recently published in the Journal of Climate, of which Abatzoglou is a co-author, found that large fires in North America are seven times more likely to ignite during persistent summer heat waves. Numerous studies have linked increasingly frequent and intense heat waves, as well as increased wildfire activity and area burned, to human-induced climate change.
Even with a cooling expected next week, fire danger is expected to remain high in the state through August, and strong fall “offshore” winds can arrive as early as September.
“It will mean the door will be opened for ignitions to become problematic fires,” Abatzoglou wrote. “Widespread dry lightning…as well as wind events are certainly things to watch as they have the potential to dramatically alter the course of the 2022 fire season if they materialize.”
Jason Samenow contributed to this report.
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