Historical records show the U.S. West Coast exhibits a wide range of extreme precipitation during the winter. Understanding the large-scale environmental influences—or forcing—that contribute to this variability is important for improving predictions of regional climate. Scientists at the U.S. Department of Energy's Pacific Northwest National Laboratory led a study to investigate the relative contributions of sea surface temperature (SST) and atmospheric dynamics to the year-to-year variability of extreme precipitation over the U.S. West Coast. They found that SST forcing accounted for only about 20 percent of the variances of winter extreme precipitation. The remaining 80 percent of extreme precipitation variations were associated with atmospheric dynamics, which are harder to predict than the slowly evolving SST.
Extreme precipitation poses significant risks to human life and property, and challenges water management by causing flooding, landslides, and related hazards. Along the U.S. West Coast, extreme precipitation is marked by significant variability that is not fully understood or adequately simulated by models. This study ruled out SST forcing in favor of difficult-to-predict atmospheric variability as the primary influence on year-to-year winter extreme precipitation along the U.S. West Coast. Applied to the winter of 2016–17, the results suggest limited predictability for the multiple landfalling atmospheric rivers and the extreme precipitation that battered California.
Reference: L Dong, LR Leung, FF Song, and J Lu, 2018. "Roles of SST versus internal atmospheric variability in winter extreme precipitation along the U.S. West Coast." Journal of Climate 31, 8039-8058 (2018). [http://doi.org/10.1175/jcli-d-18-0062.1.]