Climatology of Atmospheric Rivers across the Western United States

Atmospheric rivers (ARs) frequently impact the West Coast of the United States during the cool season (November – April). Transporting large amounts of water vapor, the arrival of these features can be associated with high impact weather, including heavy rainfall and flooding in California, Oregon, and Washington (Ralph et al. 2006; Neiman et al. 2008). While much has been learned about ARs and their impacts in these Pacific states, less is known about their penetration into the interior of the western United States, including their contribution to regional weather and climate. Using reanalysis data, we construct a climatology of ARs across the western United States, inclusive of both the coastal and interior regions. Analysis of this climatology highlights preferred corridors of moisture transport into the interior during AR events. In addition, we show that precipitation occurring in the vicinity of these ARs accounts for a large fraction of the total precipitation across the western United States, particularly the southwestern region.