The first significant storm of the season brought snow and downpours to Southern California that doused wildfires and caused some ash and mud to flow across streets in the Los Angeles area on Monday.

Heavy rain beginning Sunday afternoon caused some mudslides, and snow closed part of Interstate 5 near Los Angeles.

Because of the recent wildfires, parts of Southern California are vulnerable to mudslides, mudflows, and landslides. Ash and debris are created when trees and other objects are burned in wildfires, and this can cause the ground to become slick.

When a wildfire burns trees and anything like trees or vegetation, it burns so hot that anything in that vegetation being burned is vaporized, or turned into a gas.

The weather provided relief for crews working to contain wildfires, though rain over a burn area ups the chances of flooding and mudslides

Much-needed rain has begun to fall over Southern California, bringing relief to the drought-stricken region but also the threat of toxic runoff.

Snow shut down a key interstate north of Los Angeles for hours on Monday while weekend downpours doused wildfires across Southern California in the first significant storm of the season for the region that had not seen rainfall for eight months.

More rain fell Monday on parts of Southern California after causing mudflows over the weekend, helping firefighters but boosting the risk of toxic ash runoff in areas scorched by Los Angeles-area wildfires.