"Extraordinary torrential downpours" flood Southern California

A storm that's been flooding Southern California streets with historic rainfall, disrupting travel and prompting water rescues and evacuations is expanding into the Southwest on Friday.

The big picture: The slow-moving storm on Thursday morning dumped a month's worth of rain in one hour on Oxnard, a Ventura County city west of Los Angeles. As of Friday morning, more than 26 million people were under flood watches from Southern California to Central Arizona.

Why it matters: The "dramatic" storm has already unleashed historic rainfall rates. Daniel Swain, a climate scientist with UCLA, said during a Thursday briefing that the Ventura County downpour is likely "the heaviest rainfall that has been observed in this area in recorded history and is likely a multi-centennial kind of event,"