The role of horizontal thermal advection in regulating wintertime mean and extreme temperatures over interior North America during the past and future

Horizontal thermal advection plays an especially prominent role in affecting winter climate over continental interiors, where both climatological conditions and extreme weather are strongly regulated by transport of remote air masses. Interior North America is one such region, and it experiences occasional cold-air outbreaks (CAOs) that may be related to amplified Arctic warming. Despite the known importance of dynamics in shaping the winter climate of this sector and the potential for climate change to modify heat transport, limited attention has been paid to the regional impact of thermal advection. Here, we use a reanalysis product and output from the Community Earth System Model’s Large Ensemble to quantify the roles of zonal and meridional temperature advection over the central United States during winter, both in the late twentieth and late twenty-first centuries. We frame our findings as a “tug-of-war” between opposing influences of the two advection components and between these dynamical forcings vs. thermodynamic changes under greenhouse warming. During both historical and future periods, zonal temperature advection is stronger than meridional advection east of the Rockies. The model simulates a future weakening of both zonal and meridional temperature advection, such that westerly flow provides less warming and northerly flow less cooling. On the most extreme cold days, meridional cold-air advection is more important than zonal warm-air advection. CAOs in the future feature stronger northerly flow but less extreme temperatures (even relative to the warmer climate), indicating the importance of other mechanisms such as snow cover and sea ice changes.