A warming climate complicates everything. Hotter and drier seasons mean that big fires in December, once almost unheard of, are now common.
In earlier decades, fires late in the year might have sputtered out after hitting hillsides wet with winter rain. More recent blazes feasted on vegetation that has been sucked of moisture by persistent drought.
Even years of plentiful rain harbor dangers. Post-fire precipitation, especially very wet winters, can usher in the growth of non-native shrubs and grasses that burn quickly and spread fires faster than native species.