Leveraging the Atmospheric River Framework to Categorize Top-Decile Precipitation Regimes in Colorado

October 6, 2025

A short communication titled “Leveraging the Atmospheric River Framework to Categorize Top-Decile Precipitation Regimes in Colorado” was published in Geophysical Research Letters by Suma Battula, Jay Cordeira, Deanna Nash, Jon Rutz, and Marty Ralph from CW3E. This research was sponsored by NOAA Cooperative Institute for Research to Operations in Hydrology (CIROH), and Miramar Charitable Foundation on behalf of Eaton and Margaret Scripps. This study investigated four top-decile precipitation regimes in Colorado using a k-means clustering approach (Figure 1). The contribution of inland penetrating atmospheric rivers (ARs) from the West Coast and Gulf of America within these regimes was computed using ERA5 AR catalog (Figure 2; Guan & Waliser, 2024. This work advances the Atmospheric Rivers and Extreme Precipitation Research, Prediction, and Applications priority identified in CW3E’s 2025-2029 Strategic Plan

Previous research demonstrated the pathways by which inland penetrating ARs landfalling along the West Coast influence precipitation across Colorado. However, the role of Gulf Coast ARs on Colorado precipitation has been largely unexplored. Zou et al. (2025) highlighted the role of a strong Central Plains AR in the development of March 2019 bomb cyclone that led to widespread hazardous weather and extreme precipitation in Colorado. Recent work by Nash et al. (2025) demonstrated that a significant top-decile precipitation along the Colorado Front Range is influenced by ARs with moisture originating from the Gulf of America. Building on this work, Battula et al. (2025) classified top-decile precipitation regimes in Colorado over a 43-year period and quantified regime-wise contribution of Gulf Coast ARs (Figure 4).

Two cool-season regimes featured northwesterly and southwesterly integrated vapor transport (IVT) impacting western Colorado, characterized by a high frequency of anomalous landfalling West Coast ARs that penetrated inland facilitated by an upstream trough over the Intermountain West. Another cool-season regime with southeasterly IVT impacting eastern Colorado was characterized by anomalous Gulf of America ARs facilitated by a trough and cut-off low over the Great Plains. In contrast, a warm-season regime is influenced by IVT from Gulf of America ARs facilitated by the North Atlantic subtropical high and the North American Monsoon circulation, impacting southeastern and southwestern Colorado.

Overall, Colorado receives 32% of top-decile precipitation from inland-penetrating West Coast ARs and 43% from Gulf of America ARs. This categorization of top-decile precipitation into AR-related versus non-AR related is useful for the purposes of storm-typing to aid forecasting and water resources management.

Figure 1. (a) Topography (shaded) and HUC8 watersheds boundaries in CO (red contours). (b) Monthly distribution of top-decile precipitation days. The pie chart shows the fraction of these days in each regime and (c) Spatial distribution of AR fraction across the four top-decile precipitation regimes in CO. From Figure 1 in Battula et al. (2025).

Figure 2. Annual distribution of top-decile precipitation from inland penetrating West Coast ARs, Gulf of America ARs, and non-ARs in (a) regime 1, (b) regime 2, (c) regime 3, and (d) regime 4. From Figure 5 in Battula et al. (2025).

Battula, S. B., Cordeira, J. M., Nash, D., Rutz, J. J., & Ralph, F. M. (2025). Leveraging the atmospheric river framework to categorize top‐decile precipitation regimes in Colorado. Geophysical Research Letters, 52(18), e2025GL117528. https://doi.org/10.1029/2025GL117528

Guan, B., & Waliser, D. E. (2024). A regionally refined quarter-degree global atmospheric rivers database based on ERA5. Scientific Data, 11(1), 440. https://doi.org/10.1038/s41597-024-03258-4

Nash, D., Rutz, J. J., Cordeira, J., Zhang, Z., Ralph, F. M., Sanders, K., & Walter, E. (2025). A Trajectory‐based method for estimating the contribution of landfalling atmospheric rivers to top‐decile precipitation across Colorado. Journal of Geophysical Research: Atmospheres, 130(17) ,e2025JD043580. https://doi.org/10.1029/2025JD043580

Zou, X., Cordeira, J. M., Bartlett, S. M., & Ralph, F. M. (2025). A case study of an exceptional atmospheric river and explosively deepening cyclone over the US central plains in March 2019. Journal of Geophysical Research: Atmospheres, 130(1), e2024JD042309. https://doi.org/10.1029/2024JD042309