About five dozen firefighters have been dispatched to a brush fire that broke out in the hills above Glendora near the edge of the Angeles National Forest early Thursday morning.
The fire started just before 6 a.m. near the intersection of Glendora Mountain Road and Colby Trail Motorway, said Miguel Ornelas of the Los Angeles County Fire Department.
Ornelas said that although the blaze was technically in Glendora, forest crews were also joining in the fight.
There was no immediate estimate of the size of the fire or when crews might have it under control.
The circumstances are such that if a fire were to ignite, "there could be rapid spread of wildfire," the weather service warned Thursday.
The weather service said the unseasonably warm weather and Santa Ana winds were the result of high pressure near the surface of the Great Basin coupled with high pressure aloft just west of Southern California, blocking storm systems from reaching the region.