A Trajectory‐Based Method for Estimating the Contribution of Landfalling Atmospheric Rivers to Top‐Decile Precipitation Across Colorado

Abstract Atmospheric rivers (ARs) play an important role in weather and hydroclimate throughout the western U.S., and extensive knowledge of AR frequency, intensity, impacts, and key meteorological processes has been developed primarily focused on the U.S. West Coast landfalling ARs. Relatively limited research has examined AR characteristics further inland, particularly for Colorado (CO), where high and complex topography, as well as the distance from the coast, complicate attempts to track ARs, AR‐derived moisture, and AR‐related impacts. Previous research efforts attributing precipitation to ARs based on their spatial footprint have yielded less than 30% of cool‐season precipitation in CO as related to ARs. However, a large volume of anecdotal evidence suggests that ARs play a larger role in CO precipitation, but this requires quantitative investigation. We used trajectory‐based methods to explore the role of landfalling ARs, their moisture pathways, and their contribution to top‐decile precipitation in sub‐basins throughout CO. Moisture sourced from landfalling ARs affects this area more frequently, penetrating inland along relatively low‐elevation corridors through the Interior West, and exhibit substantial geographic and interannual variability. The backward trajectory approach for attributing precipitation to landfalling ARs yields mostly higher AR contributions to top‐decile cool‐season precipitation (21%–78%), primarily affecting western CO. Most of the AR‐related precipitation across western CO during the cool season is sourced from landfalling ARs near Southern California, the Baja peninsula, and the Pacific Northwest. These results indicate a larger role for ARs in CO weather and hydroclimate than previous research suggests.