A “once in a decade” bomb cyclone is sweeping through the northwest United States and parts of Canada early Wednesday –– leaving at least one person dead and hundreds of thousands without power across Washington state,

More than 500,000 energy customers across the West Coast were without power early Wednesday and one person was killed by a falling tree as severe weather caused by back-to-back powerful storm systems began battering the Pacific Northwest.

Bomb cyclone is a term used by weather enthusiasts to describe a process that meteorologists usually call bombogenesis. It’s the rapid intensification of a cyclone in a short period of time, and it can happen during powerful storms such as the one northern California and the Pacific Northwest are preparing for this week.