A historic heat dome is causing unprecedented high temperatures across the United States, breaking March temperature records in 14 states. Arizona set a new national March record of 112°F (44°C), which was surpassed the following day. Climate scientist Daniel Swain has described this event as one of the most extreme observed in the Southwestern U.S. The heat dome is expected to affect 28 states, with forecasts indicating that approximately 540 additional high-temperature records could be neared, tied, or broken. This heatwave is not confined to the Southwest; it is projected to spread across the Plains, Midwest, and Southeast, potentially endangering millions.