Atmospheric rivers – what to know about the storms inundating the Pacific north-west

This week's weather system dumped 5tn gallons of rain on Washington state - and another one is threatening Canada

Just as record-level flood waters that triggered widespread evacuations begin to recede in western Washington state, residents of the Pacific north-west are bracing themselves for another strong weather system that is likely to swell rivers back to dangerous levels - again.

An extraordinarily strong system known as an atmospheric river hit the region earlier this week, dropping more than a foot of rain and flooding rivers that stretch across the state toward Canada to dangerous levels. As a result of the nonstop rain, mudslides tore through communities, washing away homes and stranding families on rooftops as they waited for rescue.