Officials predict ‘active' fire season in California. Here's where conditions could be worst

San Francisco Chronicle​

17-05-2025

California's door for rain is closing quickly and wildfire season is around the corner.
On the heels of last year's dynamic season, which featured the state's fourth-largest blaze in history and culminated in January's deadly Los Angeles-area infernos, officials expect another year of fierce fires. Above-normal wildfire activity is predicted throughout much of California in July and August, according to the National Interagency Fire Center.
'Overall, an active fire season is what I'm predicting,' said Brent Wachter, a fire meteorologist with the Northern Operations Predictive Services unit.
Officials say the hot summer forecast combined with lush and likely very flammable vegetation, are fueling the active outlook.
Grasses are thick across Northern California after a healthy dose of winter rain. Most areas north of Interstate 80 received above-normal precipitation from October through May, which could tame the fire season at first, particularly in forested areas. But grasses are predicted to become flammable throughout June, especially in the valleys between the Coastal Ranges and Sierra Nevada.
Measurements from May 1 found the grass crop to be 41% more dense than an average year in Browns Valley (Yuba County) at the Sierra Foothill Research and Extension Center, a center under the University of California Division of Agriculture and Natural Resources.
Grass is even thicker this year than in spring 2024 at the Browns Valley site. That summer, a bulletin issued by Cal Fire and other agencies warned of tall grasses contributing to rapid fire spread following a July heat wave.
With plenty of vegetation available across California, the stage is set for big fires this summer if hot, dry windy weather aligns with a spark.
'I firmly believe if everything is projected right with the heat and dryness, that we're going to have some flash drought conditions develop, similar to what we had last year,' Wachter said.
Grasses and shrubs in mountainous areas will probably be ready to burn by the second half of July, contributing to the above-normal wildfire potential in the Sierra, Wachter said. An early melt-off of California's snowpack means mountainous areas could dry up earlier than normal and allow wildfires to spread more rapidly.
Central and Southern California forecast
Central and Southern California picked up significantly less rainfall this winter. Drought has already emerged in many areas. However, rain that fell from late February to April spurred grass growth across Southern California, according to Jonathan O'Brien, a fire meteorologist with the Southern Operations Predictive Services unit.
'It only takes a couple weeks of hot and dry weather to really start zapping the finer vegetation and even into some of the heavier fuels,' O'Brien said.
There is a slight tilt in the odds toward above-normal large fire potential in the Sierra foothills, the Southern Sierra, the Central Coast, the Transverse Ranges and the South Coast in July and August, according to the National Interagency Fire Center.
Seasonal forecasts from multiple agencies predict above-normal temperatures from June through August, especially in the inland valleys and Sierra foothills. California typically lacks meaningful rainfall during summer, except in the mountains where the North American Monsoon can yield occasional thunderstorms.
The hot, dry outlook suggests elevated fire weather conditions across much of inland California by midsummer as heat combines with ignition risks such as Santa Ana and Diablo winds.
'Warm summers predispose forested parts of the state to enhanced fire potential by curing fuels,' said John Abatzoglou, a climatologist at UC Merced. 'Years with significant and widespread heat waves have often ended up with plenty of fire.'
Short-term weather drivers, like heat waves and tropical moisture intrusions that can bring lightning risks, will shape week-to-week fire danger.
The outlook for those monsoonal intrusions is muddled. The Climate Prediction Center shows a slightly increased chance of above-normal precipitation across parts of Arizona and New Mexico in July, but it's unclear how that could play out in California. Abatzoglou points out that the lingering effects of a weak La Niña have left behind cool ocean waters near California, which could 'pad fog and abate summer fire danger' in coastal areas through June.
Andrew Hoell, a scientist at NOAA's Physical Sciences Laboratory, said that the broader weather setup is unclear this early in the season.
'The key players this summer will be the large-scale atmospheric patterns, where ridges and troughs set up, and whether they persist,' Hoell said. 'But we don't tend to have a lot of forecast skill for those features beyond a few weeks.'
July may mark a turning point: more heat waves and increasing lightning potential setting the stage for fast-moving shifts in fire danger.
'Lightning is a huge wildcard,' Abatzoglou said. 'Monsoonal surges or other lightning outbreaks can quickly turn a dull fire season into an extremely active one.'