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

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.

Potentially critical fire weather is likely to arrive in San Diego Tuesday and worsen into mid-week, with Santa Ana winds setting in amid dry conditions.

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.