A weather system affecting northwest California is expected to bring dry lightning and blustery winds.
That unleashes the risk of new wildfires as thousands of firefighters are making headway against existing blazes.
A warning for dangerous fire weather has taken effect in much of fire-scarred Northern California on Thursday afternoon and may last through Friday.
The new threat comes as the California Department of Forestry and Fire Protection says firefighters have been making significant progress against the fires.
More than 14,600 firefighters are on the lines of 13 big wildfires in California.