The heat wave has already claimed at least 20 lives, with millions still under heat alerts in the Southwest and Alaska. In Phoenix, dangerously high temperatures pose significant health risks, particularly for vulnerable populations. Northern Alaska, unaccustomed to such heat, faces increased risks of heat-related illnesses. Meanwhile, the Northeast and Mid-Atlantic are experiencing heavy rainfall and flash flooding risks due to a slow-moving frontal boundary. The heat dome's westward shift is expected to exacerbate fire activity and reduce air quality in the Rockies and High Plains.