Bar chart showing change in the average length of heat waves in 50 major U.S. metro areas from 1961 to 2023. Overall, heat waves in big cities are getting 1.4 days longer, with the greatest increases in New Orleans (4.5 days longer), followed by Fort Worth, Texas (4 days) and Salt Lake City (3.7 days). In Seattle, heat waves have gotten 2.1 days longer.