Forecasters now have real-time access to an experimental forecast model developed specifically for atmospheric rivers. Early results show it does well with predicting events with high precipitation amounts, which are the most impactful to public safety and managing water resources such as reservoirs.
The Atmospheric River Analysis and Forecast System, or AR-AFS, is built on the successful research and development of the Hurricane Analysis and Forecast System, which is enabled by sharing the same core code. But instead of tracking tropical systems, it follows the long streams of tropical moisture over the Pacific Ocean that deliver as much as half of the rain or snow that contribute to West Coast water supply. It gives daily updates up to five days in advance, showing the amount of water vapor, where it’s moving, and how much rain or snow is expected over a 24-hour period.
AR-AFS stands out from other models for two main reasons. First, it has a higher resolution, letting it better “see” the complex terrain of the West Coast and the small-scale weather features that cause locally heavy precipitation. Second, it’s connected to another model that simulates important ocean processes that drive the location and intensity of atmospheric rivers.
Forecasters and other stakeholders can see AR-AFS precipitation forecasts on an interactive map through the Global Systems Laboratory’s DESI website.
NOAA will gather feedback while doing further model development and testing. AR-AFS could move from being an “experimental” model to an “operational” one — used for official, everyday use — by autumn 2028.
Developing and evaluating this forecast model is just one component of NOAA’s broader initiative to improve AR forecasts, titled the Atmospheric Rivers Forecast Improvement Project. Other aspects include investigating economic impacts of ARs and how observations from aircraft and balloons affect model accuracy.
The project is a collaboration among among NOAA’s Weather Program Office, Global Systems Laboratory, Physical Sciences Laboratory, Weather Prediction Center, Environmental Modeling Center, and Air Resources Laboratory; the Cooperative Institute for Research to Operations in Hydrology (CIROH); and the Center for Western Weather and Water Extremes (CW3E).
This story was published on March 17, 2026.
