In California there is often too much or too little water. This was exemplified recently by the need for water-use restrictions during the severe drought from 2012 to 2016, followed immediately by a water surplus in water-year 2016-2017 that nearly caused northern California's Oroville Dam to overflow (Wang et al., 2017). Despite over a century of record keeping and management strategies that address this variability, the volatility of precipitation in California continues to pose major challenges to water resource managers. Management must minimize effects of drought on water supplies while also keeping reservoir levels low enough to minimize flood risk (Dettinger et al., 2011; Hanak et al., 2017; Stewart et al., 2020). California's exposure to hydrological volatility is particularly high because of its geographic setting: the majority of the state's surface water supply falls in the Sierra Nevada during the relatively short cool season of November-March (Dettinger, 2013; Dettinger et al., 2011, 2018), giving this region and season particular importance to California's water resources. While parts of the state, especially southern California, have worked to diversify water portfolios with a combination of surface, imported, and ground water, and to employ conservation measures and water markets (Gottlieb & FitzSimmons, 1991; Lund et al., 2018), California remains vulnerable to extreme variability of precipitation (Swain et al., 2018). Extreme hydrological shortages in the Sierra Nevada can be only moderately buffered by water supplies in regions and seasons not experiencing drought. California's drought and flood risk is amplified by the limited reliability of seasonal forecasts of Sierra Nevada precipitation (Jones et al., 2015). While forecast skill beyond a 2-week horizon is inherently poor globally, seasonal forecasting for parts of the western United States is aided by a teleconnection to the El Niño-Southern Oscillation (ENSO) (Huang et al., 2019; Seager & Hoerling, 2014). This is not the case, however, for the Sierra Nevada, which span the neutral point of the ENSO dipole that often drives Abstract California's water resources rely heavily on cool-season (November-March) precipitation in the Sierra Nevada. Interannual variability is highly volatile and seasonal forecasting has little to no skill, making water management particularly challenging. Over 1902-2020, Sierra Nevada cool-season precipitation totals exhibited significant 2.2-and 13-15-year cycles, accounting for approximately 40% of total variability and perhaps signifying potential as seasonal forecasting tools. However, the underlying climate dynamics are not well understood and it is unclear whether these cycles are stable over the long term. We use tree rings to reconstruct Sierra Nevada cool-season precipitation back to 1400. The reconstruction is skillful, accounting for 55%-74% of observed variability and capturing the 20th-century 2.2-and 13-15-year cycles. Prior to 1900, the reconstruction indicates no other century-long periods of signif...