[RayChuang88]

However, we are not likely going to have that debacle in December 1997 when Sacramento came within a hair's breadth of very severe flooding from the American and Sacramento River overflowing its banks.

After that debacle, the US Bureau of Reclamation completely changed its procedures on opening the spillways at Folsom Dam and Natomas Dam and the flood gates at Sacramento Weir. As such, if we suddenly have a lot of rain the spillways will be opened much earlier and will be like what happened in the winter of 2010-2011, when 200% normal rain did not cause any flood danger issues in the Sacramento, CA area (though there was just a tad too many small tornadoes touching down in the Central Valley that winter).

[Mariner]

It's not unheard of for great floods to come to northern California:

The entire Sacramento and San Joaquin valleys were inundated for an extent of 300 miles (480 km), averaging 20 miles (32 km) in breadth.[16] John Carr wrote of his riverboat trip up the Sacramento River when it was at one of its highest stages of flood:

From the flood of 1862. It snowed all the early winter, deep snow in the mountains.

Then came the Pineapple Express and warm rain...with Rainfall in one 36hr period measured at 9 inches.

The entire Central Valley was like one of the great lakes.