Atmospheric river

"The intense rainstorms sweeping in from the Pacific Ocean began to pound central California on Christmas Eve in 1861 and continued virtually unabated for 43 days."

"What’s not normal is to have atmospheric river events that are this large. [in terms of rainfall these events] are nearly equaling the historic record."

"Warmer atmospheric temperatures, in general, will mean the freezing levels are higher than they've been in the past. But while storms vary, even without climate change and some can be extra warm, just by natural situation, it's clear the background warming should increase the [freezing] levels. This makes for extra potential potency to the impact," he said. "The rivers are already high again, so this one's going to pack a wallop."