California storms to get a rating from 1 to 5, like hurricanes – SFChronicle.com
Like a monster hurricane, a Category 5 atmospheric river is something to watch out for, a days-long deluge like what threatened to topple Oroville Dam two years ago. Such drenchers can bring as much rain as the strongest of Atlantic storms and cause life-threatening floods, mudslides, downed trees and power outages. A Category 1 atmospheric river, by contrast, means modest rainfall.
The categories are necessary to cut through the hype that has surrounded atmospheric rivers in recent years, say the team of state, federal and university scientists behind the ratings. These long plumes of moisture that move with the jet stream, while a relatively new concept for California households, already have a larger-than-life reputation. After dozens blew through during the winter of 2016-17, the most in decades, many people associated them with disaster.