A bomb cyclone occurs when cold and warm air collide over the ocean, dropping the pressure at a rapid rate and creating intense weather. On the East Coast, that can mean vast quantities of snow. Here on the West Coast, it can usher in buckets of rain.

The West Coast is preparing for a long-duration heavy rain event from a bomb cyclone set to form Tuesday. Threat level: The rapidly intensifying storm, taking shape in the northeastern Pacific Ocean,

Starting Tuesday, the Pacific Northwest could get at least 6 inches of rain, with 20-plus inches possible in the mountains. Strong winds could cause power outages.