Parts of Northern California that saw up to half a foot of rain last weekend are bracing for more this week as a series of powerful storms up and down the West Coast threatens to bring scattered flooding, mudslides and debris flows in the lower elevations and heavy snow in the mountains.

Parts of Southern California, where an exceptionally dry winter helped fuel multiple wildfires last month, are expected to see rain from Tuesday through Friday that could raise the threat of mudslides in some areas.

The storms, known as atmospheric rivers, are ribbons of moisture carried by powerful winds, and the first of three in a row occurred this weekend; it stretched roughly 2,500 miles from Hawaii to California like a conveyor belt bringing tropical water vapor to the north. Nearly six inches of rain fell on Saturday and Sunday in places like Redding, Calif., which caused some roads to flood.

The second of these storms is expected from Monday into Wednesday. Flood watches were issued for roughly 13 million people across Northern California from Monday afternoon through Wednesday morning, including heavily populated areas like the San Francisco Bay Area and Sacramento Valley. (A flood watch means residents should be prepared for possible flooding; it does not mean that flooding will occur.)

That thin strip of moisture, only about 100 to 200 miles wide, might not be as long as the first, but for much of this week, it will meander along the West Coast like an uncontrolled fire hose. It is expected to drench Northern California before drifting south, bringing some rainfall to Southern California.