Dozens of communities are now under mandatory evacuation orders in Southern California with evacuation warnings affecting dozens more as crews continued battling a pair of deadly wildfires in the region Friday.

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.