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,

Dire warnings have been issued for the Los Angeles area, with a dangerous threat for the strongest wind event in more than a decade. Outages and extreme fire behaviours are major risks

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.