Dozens of communities are now under mandatory evacuation orders in Southern California with evacuation warnings affecting dozens more as crews continued battling a pair of deadly wildfires in the region Friday.

Red flag criteria is generally when relative humidity is at 15% or less, combined with sustained winds and/or gusts of 25 mph or greater. Both of these conditions must occur simultaneously for at least 3 hours in a 12 hour period, according to the NWS.

Another round of Santa Ana winds has moved into Southern California and will spread south through San Diego County late Thursday. The additional dry air also is expected to worsen the region’s already very low humidity levels,

The National Weather Service has issued a Red Flag waning for a wide swath of Southern California as Santa Ana winds are expected to bring dangerous fire weather to the region later this week.

The alert status for heightened combustion hazards in the county's inland valleys and mountains went into effect at 4 a.m. Wednesday and will last until 6 p.m. Friday.

A Red Flag Warning has been extended for portions of San Diego County ahead of another bout of strong Santa Ana winds.

The winds will come and go, with the strongest gusts expected early next week, especially next Monday night and into Tuesday, forecasters said.

Although the strongest wind gusts have passed through the Southern California region, another "traditional Santa Ana wind event" will move in Thursday night.

Red Flag Warnings remain in effect through Friday evening for much of Los Angeles and Ventura Counties, the National Weather Service said.