The Role of Atmospheric Rivers in the Snowpack over the Upper Colorado River Basin during Water Year 2023

The Colorado River is the most important surface water source in the U.S. Southwest. The natural streamflow of this river is mainly generated by the snowpack in the Upper Colorado River Basin (UCRB), which experiences large year-to-year variability. Atmospheric rivers (ARs) can transport substantial amounts of water vapor from coastal regions into the interior western U.S., significantly influencing inland precipitation, including snowfall in the UCRB. During water year (WY) 2023, an unusually large number of ARs made landfall along the U.S. West Coast, penetrating inland and bringing heavy precipitation over the western U.S. This study investigates the influence of ARs on the snowpack across the UCRB and its sub-basins during WY 2023. Snow water equivalent (SWE) data from the snowpack telemetry (SNOTEL) stations across the UCRB is used to analyze the snow accumulation and the extreme snow events. The integrated water vapor transport (IVT) and other relevant fields from ECMWF Reanalysis version 5 (ERA5) are utilized to examine the AR characteristics and the related large-scale weather patterns. The contributions of inland AR penetration are quantified across the sub-basins and the preferred AR penetration pathways are explored. Preliminary results show that the southward shift of the AR activity over the eastern North Pacific and the corresponding inland AR penetrations played a critical role in the positive anomaly in the snowpack over the UCRB during WY 2023. This case study of the wet WY 2023 contributes to improving the understanding of the linkage between landfalling ARs over the West Coast and the interior snow over the western U.S.