A storm is dropping rounds of heavy rain on more than 22 million people across Southern California on Saturday, and the rainfall could spark dangerous flash flooding, mudslides and debris flows. The first round of heavy rain is slamming the region early Saturday morning, and the second round will hit between 11 a.m. and 4 p.m. local time.

The most powerful band of a large atmospheric river storm slammed into Southern California on Saturday, dumping much-needed rain across the region but also bringing mudslide dangers.

A Pacific storm could help California crews battle the dangerous Pack Fire in Mono County, but it could also wreak havoc on fire-charred communities further south.

Heavy rain continues to pound Southern California today. The National Weather Service expects 2 to 3 inches will fall over the next 24 hours. That could push the storm's total over 6 inches in some locations.

The rain could also lead to washed-out roads, debris flows and damaging winds – making travel difficult or dangerous, forecasters warn.

If rain falls as forecast, this storm could result in downtown Los Angeles seeing its wettest November since 1985. Heavy rain brings the possibility of damaging flooding and landslides.