California is preparing for the possibility of significant atmospheric river activity next week, with forecasts calling for an increased risk of heavy rainfall, mountain snow and strong winds across portions of the West Coast.
The National Weather Service’s Climate Prediction Center issued an outlook on November 5 identifying the potential for multiple storm systems to affect California and the Pacific Northwest between November 13 and 17.
Northern California currently has the greatest potential for significant precipitation. The forecast indicates a 40% to 60% probability of heavy precipitation across portions of the Pacific Northwest, Northern California and Central California between November 13 and 15. Higher elevations of the Sierra Nevada and Klamath Mountains could also experience substantial snowfall.
Southern California and portions of the Desert Southwest face a 20% to 40% precipitation risk through November 17.
Atmospheric rivers are long, concentrated corridors of water vapor that transport moisture from tropical and subtropical regions toward the West Coast. These systems can produce substantial rainfall and snowfall, helping replenish reservoirs, increase streamflows and contribute to California’s seasonal water supply.
For the state’s fisheries and seafood industries, the seasonal arrival of precipitation has important implications for freshwater availability, river conditions and aquatic ecosystems. Rainfall and snowpack contribute to reservoir storage and groundwater recharge, while freshwater flows help sustain rivers, estuaries and other important fish habitats.
At the same time, intense atmospheric river events can create challenges for fisheries and coastal communities. Heavy runoff can increase sedimentation, transport pollutants and nutrients into waterways, alter salinity and water temperatures, and contribute to flooding. These conditions can affect aquatic habitat, fish migration and water quality.
The developing forecast is particularly noteworthy given expectations for a strong El Niño this winter. Although El Niño is often associated with wetter conditions in Southern California, scientists emphasize that individual atmospheric river events can produce precipitation patterns that differ considerably from typical seasonal expectations.
Researchers at UC San Diego’s Center for Western Weather and Water Extremes note that atmospheric rivers can disrupt the precipitation patterns commonly associated with both El Niño and La Niña. Consequently, regional impacts can vary considerably from one storm system to another.
Forecast confidence remains limited, and meteorologists caution that it is too early to determine exactly where the storms will make landfall or how much precipitation California will receive. The National Weather Service and Climate Prediction Center will continue refining their forecasts as the systems approach.
Why it matters: Atmospheric rivers are a major driver of California’s annual water supply and play an important role in shaping freshwater and coastal ecosystems. Their ability to replenish water resources must be balanced against the potential for flooding, runoff and water quality impacts. Monitoring these storm systems will be important for fisheries businesses, seafood operations and communities throughout the state.