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.

That’s leading to the creation of mountain waves, which arise when strong winds blow perpendicular to a mountain range. The waves shoot down the coastal side of the mountains, gaining speed along the way, and are more casually referred to as simple Santa Ana winds.

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.

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.

San Diego County, which is in the midst of one of the driest periods on record, will be lashed by unusually cold and expansive Santa Ana winds early Wednesday that could spark wildfires, snap

The National Weather Service has issued a Red Flag Warning for San Diego County due to high winds and low humidity.

San Diego Gas & Electric began public safety power shutoffs Tuesday as San Diego County braces for a Santa Ana wind event and Red Flag Warning.

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

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.

In San Diego, the Red Flag Warning for inland and mountain communities has been extended until at least 6 p.m. Friday, so our county remains on high alert due to the elevated fire risk. ABC 10News is bringing you extensive coverage on both the Los Angeles fires and how our area is preparing for the worst in this edition of the Wake Up Call newsletter.