Heat-dome-like stationary waves (SWs) often lead to extreme events, such as the unprecedented heatwave in Northwestern North America (NNA) during the summer of 2021. Understanding the projected changes of heat-dome-like SW circulation is crucial for adapting to and mitigating the impacts of future heatwaves. However, the projected changes in summertime SW circulation over NNA region and the underlying driving mechanisms remain unclear.

Here focusing on the projected changes in SW circulation over NNA region, we identify the dominant physical processes driving those changes. Our findings reveal a robust strengthening of the anticyclonic circulation in the upper troposphere by 65% (–17%~147%) at the end of the 21st century under the high emission scenarios by using data from the Coupled Model Intercomparison Project Phase 6. Sensitivity experiments using the stationary wave model isolate the diabatic heating from the tropical eastern Pacific as the dominant driver. The dipole changes in diabatic heating over the tropical eastern Pacific leads to an enhancement of the wave source over the tropical northeastern Pacific, triggering amplified Rossby waves that propagate towards NNA, with assistance from a poleward expanded waveguide. Similar dynamical processes can be captured by the idealized model forced by the tropical diabatic heating, providing a dynamical rationale for the confidence in the future increase of heat-dome-like SW circulation over NNA region. By unraveling the dominant underlying dynamical mechanisms, we gain a better understanding of the cause of projected changes in SW circulation and their implications for future heatwave changes.