By the time the winds get to the point where the Eaton Fire broke out in Altadena on Jan. 7, it’s not uncommon for them to have less than 5 percent relative humidity, meaning essentially no moisture at all.

Parts of Southern California, including Los Angeles, are under an extreme fire risk on Wednesday as Santa Ana winds continue to impact the region. The threat will lessen slightly on Thursday before ramping up again later in the week.

High-speed winds this week have the potential to knock over semitrucks and cause other hazardous driving situations. Here's what to know.