The most destructive wildfires in Los Angeles history Thursday have burned more than 54 square miles of land, destroyed thousands of structures and killed at least five people.

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.

The National Weather Service on Wednesday extended the wildfire warning through the end of the week for much of East County.

A short reprieve in the strong destructive winds has granted firefighters an opportunity to curb the spread of the deadly Eaton Fire near Pasadena.

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.

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.

ABC 10News reporter Moses Small reported live from Alpine, where wind gusts could reach 75 miles per hour in the next couple of days, elevating the fire risk for San Diego County.

Red flag warnings will linger across much of Southern California for the rest of the work week as Santa Ana winds slowly diminish but continue to blast the region at above-normal velocity and fuel fires that have burned thousands of acres.