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.

Red flag weather warning: A National Weather Service alert that warns the public — especially fire officials and firefighters — that strong winds are expected in specific areas of Southern California, and that there will be potentially dangerous fire weather conditions within the next 12 to 24 hours.