Dry lightning and blustery winds in California are unleashing a risk of new wildfires as thousands of firefighters have been making headway against existing blazes.

A warning for dangerous fire weather took effect in much of fire-scarred Northern California.

“The combination of isolated dry lightning and gusty winds with the dry fuels will bring the potential for critical fire weather conditions,” the National Weather Service said.

A historic drought and recent heat waves tied to climate change have made wildfires harder to fight in the American West. Scientists say climate change has made the region much warmer and drier in the past 30 years and will continue to make weather more extreme and wildfires more frequent and destructive.

More than 14,600 firefighters were on the lines of 13 active, large wildfires in California on Thursday.

The Dixie Fire in the northern Sierra Nevada and southern Cascade Range grew to about 1,451 square miles but was 59% contained. It is the second-largest California fire on record.

Only last year’s August Complex was larger, at just over 1,613 square miles. Near Lake Tahoe, the Caldor Fire grew only slightly, to just over 341 square miles, and was 53% contained.

Nationally, some 22,000 firefighters were working on 79 active, large wildfires in nine states in the West as well as Minnesota, according to the National Interagency Fire Centre in Boise, Idaho.

President Joe Biden will survey fire damage during a visit to California next week.