Precipitation models are not ready for prime time. Li et al. looked at the current generation of models (CMIP6) and found that projections for changes in California precipitation ranged from -3% to +42% for northern California and -27% to +63% in the central-southern part of the state.
Their modeling came up with increases of +10 to 34% for the north and +7 to 32% to the south. This was by the end of the century.
Wetter California Projected by CMIP6 Models With Observational Constraints Under a High GHG Emission Scenario