In other words, late-fall and winter rains would normally end California’s fire season in November. Because those rains haven’t yet arrived, the blazes continue.

“At least in Southern California right now, we are largely seeing textbook wildfires,” said Alexandra Syphard, a senior research scientist at the Conservation Biology Institute who studies fires. “Wind-driven fire events occur most typically in the fall, but can also occur like this, later in the year with fast-spreading, ember-driven fires under Santa Ana wind conditions.”

Here are some of the biggest factors that are shaping the wildfires in California—and how global warming is or isn’t changing them:

The Santa Ana winds

Blame for the wildfires in Ventura and Los Angeles counties lies first and foremost with the Santa Ana winds, famously hot and desiccating gusts that blow from the desert to the coast. The Santa Anas also set the stage for the massive wildfires in Napa and Sonoma earlier this year.

Fires depend on two variables—an ignition source and fuel to burn—and the Santa Ana winds increase the availability of both. First, they dry out vegetation, creating more fuel across the landscape. Second, they blow trees and other debris against power lines, providing the source of a spark.

When the Santa Anas blow this late in the year, they can start fires. In fact, writes Abatzoglou, “all December fires in the southland since 1948 have been associated with Santa Ana wind.”

But there are few signs—at least so far—that the Santa Ana winds are becoming more prevalent or that they’re systematically moving later in the year. The peak of Santa Ana season usually comes in September or October. There is no trend toward more or fewer Santa Ana fires—or Santa Ana winds generally—in the historical record, Abatzoglou told me.

A 2006 study from researchers at the University of California, Berkeley, and the Lawrence Berkeley National Laboratory suggested that by the end of the century, Santa Ana winds may become more common. They may also form later in the year, including in December.

La Niña

There’s currently a weak La Niña in the tropical Pacific, which means that global temperatures are cooler than they would be otherwise.

The same phenomenon is also keeping storms from making landfall in Southern California. Normally, California’s wet season would have started by this time of year. “Once [autumn] rains hit the region, fuel moistures recover and make the landscape fire-resistant, thus reducing the odds that a power-line failure or vehicle will start a fire,” said Abatzoglou.

But the rains haven’t yet appeared, he told me. “So far this autumn, much of the southern half of California is pitching a shutout in terms of rainfall to date. Some of this is characteristic of La Niña ... as the southern tier of the United States sees less precipitation during La Niña winters.”

It’s still unclear how climate change will affect the Pacific’s yearly dance between El Niño, La Niña, and a neutral state. A 2015 study in Nature Climate Change found that the Pacific Ocean may careen between extreme states—from an intense El Niño to a monster La Niña—by the end of the century, but more research on the question still needs to be done.