While the inverse relationship between antecedent snowpack in the Himalayas and Tibetan Plateau and subsequent monsoon rainfall in South and East Asia has been extensively studied and established, the potential for such a relationship between Rocky Mountain snowpack and the North American monsoon remains uncertain. The present study represents the first modeling assessment of this vital predictability issue, going beyond simple observational correlations, which fail to identify causality or a mechanism, by applying a regional climate model to demonstrate that a deep Rocky Mountain snowpack tends to hinder the poleward advance of the subtropical ridge and associated monsoon rainfall into the Southwest United States. A deep, extensive snowpack increases the surface albedo and provides an abundant surge of soil moisture, both of which reduce tropospheric temperatures in spring and early summer, weakening the land‐ocean thermal gradient and related monsoon system. This snow‐monsoon relationship, which may serve as a vital prediction tool of summer rainfall in the semi‐arid Southwest United States, has direct implications for regional water supply, streamflow, and biodiversity.

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