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Storm tracks, defined as the preferred regions of extratropical synoptic-scale disturbances, have remarkable impacts on global weather and climate systems. Causes of interannual storm track variation have been investigated mostly from a troposphere perspective. As shown in this study, Northern Hemisphere winter storm tracks are significantly modulated by the tropical stratosphere through the quasi-biennial oscillation (QBO). The North Pacific storm track shifts poleward during the easterly QBO winters associated with a dipole change in the eddy refraction and baroclinicity. The North Atlantic storm track varies vertically with a downward shrinking (upward expansion) in easterly (westerly) QBO winters associated with the change of the tropopause height. These results not only fill the knowledge gap of QBO-storm track relationship but also suggest a potential route to improve the seasonal prediction of extratropical storm activities owing to the high predictability of the QBO.

Plain Language Summary Storm tracks are regions in which the midlatitude cyclones are most prevalent. Midlatitude cyclones can cause extreme precipitation and heat/cold events over North America and Europe. Therefore, having a better understanding of how storm tracks change may help in predicting potential natural disasters. Previous studies have shown that storm tracks change from year to year as a result of tropospheric or polar stratospheric variabilities. By examining reanalysis data, we find that change in tropical stratospheric wind direction modulates significant year-to-year variation of storm tracks. In the North Pacific, the storm track shifts poleward with the easterly wind in the tropical stratosphere, while in the North Atlantic, the storm track shrinks (expands) vertically with the easterly (westerly) wind in the tropical stratosphere. These changes are associated with changes in atmospheric instability modulated by the stratospheric wind. Our findings offer an opportunity to improve seasonal forecasts of storm tracks and their extreme impacts by taking the stratospheric variability into account as a source of predictability.