There are these things called “Atmospheric rivers.” They are big long things up in the air that are loaded with water vapor, and much of the rain and other precipitation we experience comes out of them. This is notable when one of these rivers is extra wet, and there is an extra wet one out West in the US.
The Sierra Nevada range will be accumulating something like 16-20 inches of rain, but where that translates into snow, it will be up there in the 12 foot range, maybe more. There will be a very significant risk of flash flooding north of Sacremento and places in northern California and Oregon are going to get very very wet. The Bay Area will see lots of rain but mostly to the north, in Marin County.
A significant rainfall event is underway across portions of the West Coast as unrelenting Pacific moisture slams into the region. Northern California and southern Oregon will see the greatest rainfall totals of 10 to 20 inches by early next week. Strong winds and mountain snow will also impact the area.
The reason I mention this at all (those of you who live there, I’m sure, are totally up on this) is the following: This sort of excess rain is exactly what we expect to see more often because of global warming. This is the effect that global warming has on the hydrological cycle. It fills the Atmospheric Rivers with more moisture than would otherwise develop in them.