Impact of extratropical Northeast Pacific SST on U.S. West Coast Precipitation

Abstract

The rainfall over the U.S. West Coast is known to be highly influenced by large‐scale atmospheric circulation and tropical climate teleconnections. However, the role of North Pacific oceanic variability is less understood. Using high‐resolution regional atmospheric model simulations forced by sustained positive and negative phases of the extratropical Pacific Decadal Oscillation sea surface temperature anomalies (SSTa), we diagnose the precipitation changes over the U.S. West Coast during 2010–2020. We find that precipitation anomalies are up to 60% stronger (weaker) for the warm (cold) cases, especially over Northern and Central California during wintertime, and Baja California in the summertime. In both seasons, precipitation is predominantly modulated through changes in the water vapor flux, which are directed toward the coast in wintertime and away from the coast during summertime. These flux anomalies are primarily driven by large‐scale changes in the wind associated with the atmospheric adjustment to the strong ocean SSTa.Plain Language SummaryThis study examines how ocean temperature in the Northeast Pacific affects rainfall in the U.S. West Coast using computer model simulations over the period 2010–2020. Rainfall generally increases when coastal waters are warmer and vice versa. This is especially true in Northern and Central California during wintertime and in Baja California during summertime. The amount of rain is mainly affected by changes in the water vapor that moves toward the coast in the winter and away from the coast in the summer. These changes in water vapor are caused by changes in the wind, which are linked to changes in the surface ocean temperature.Key PointsWarming along the U.S. West Coast can induce wind‐driven vapor fluxes changes leading to enhanced precipitationExtratropical sea surface temperature (SST) forcing can impact large‐scale atmospheric circulationU.S. West Coast precipitation are impacted by extratropical Northeast Pacific SST