The fierce winds in the Los Angeles area subsided Friday, but critical fire weather conditions remain and red flag warnings are still in place.

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,

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.