Enhanced Highland Warming Intensifies Midlatitude Moist Heat and Convection

Extreme heat events and severe convective storms are among the leading causes of weather-related damages in North America (NA). Under climate change, western NA highlands experience a faster rise in extreme near-surface temperatures, while central and eastern NA show stronger amplification of moist heat and convective activity. In recent theoretical work, we showed that low-level energy inversions significantly contribute to the buildup of near-surface moist heat and convection in the midlatitudes. Here, we demonstrate using CMIP6 simulations that future intensification of extreme moist heat over central NA is associated with substantial warming upstream over high terrains, which is advected eastward by strong westerlies, enhancing downstream low-level energy inversions. The projected increase in inversion strength provides a tight upper bound for the projected increase in near-surface moist heat. We further validate these findings through a General Circulation Model (GCM) experiment in which eliminating elevated heating over western high terrains substantially reduces extreme moist heat and convective instability across eastern NA. Our findings identify elevated heating and low-level inversions as critical drivers of compound heat-convection risks, offering new insights into the mechanisms and projected changes of midlatitude extreme weather.