Direct and Indirect Relationships Between Atmospheric Rivers and Precipitation in Colorado

Atmospheric Rivers (ARs) are the primary drivers of flood damages and major contributors to water supply in the western U.S., and their interannual variability largely translates to drought or flood conditions. Past studies have identified pathways through the Intermountain West by which water vapor transport along West Coast landfalling ARs may reach Colorado and directly impact precipitation along the west slope of the Continental Divide. These pathways often translate to a direct relationship between ARs and enhanced snowfall, often producing significant increases in snow-water equivalent and beneficial increases to the seasonal water supply in the Upper Colorado River Basin. Over the Colorado Front Range, among other locations, there may be another pathway that provides an indirect relationship between ARs and enhanced precipitation in the state. In March 2019, rapid cyclogenesis over Southeast Colorado set the state’s minimum sea-level pressure record and produced widespread high-impact snowfall and rainfall from Southwest Colorado, over the Front Range, and east through the Upper Great Plains. This storm developed in association with poleward water vapor transport from the Gulf of Mexico along an AR with integrated vapor transport (IVT) magnitudes over eastern Oklahoma >1400 kg/ms, surpassed in intensity only by three prior IVT maxima in the last 50 years. While this AR and others emanating from the Gulf of Mexico may directly contribute to high-impact weather over the Upper Great Plains, it is hypothesized that this AR and others may indirectly contribute to high-impact weather over Colorado and the Front Range by influencing the broader synoptic-scale processes that do.