Using observations and reanalysis, we find that changes in April precipitation variations in the northwestern US are strongly linked to March Arctic stratospheric ozone (ASO). An increase (decrease) in ASO can result in enhanced (weakened) westerlies in the high and low latitudes of the North Pacific but weakened (enhanced) westerlies in the mid-latitudes. The anomalous circulation over the North Pacific can extend eastward to western North America, facilitating (impeding) the flow of a dry and cold airstream from the middle of North America to the North Pacific and enhancing (weakening) downwelling in the northwestern US, which results in decreased (increased) precipitation there. Model simulations using WACCM4 support the statistical analysis of observations and reanalysis data, and further reveal that the ASO influences circulation anomalies over the northwestern US in two ways. Stratospheric circulation anomalies caused by the ASO changes can propagate downward to the troposphere in the North Pacific and then eastward to influence the strength of the circulation anomalies over the northwestern US. In addition, the ASO changes cause sea surface temperature anomalies over the North Pacific that would cooperate with the ASO changes to modify the circulation anomalies over the northwestern US. Our results suggest that ASO variations could be a useful predictor of spring precipitation changes in the northwestern US; The northwestern US may become dryer in future springs due to ASO recovery.