An unrelenting heat wave across the southern United States is continuing today, with dozens of temperature records set to fall. In Phoenix, Arizona, where nighttime temperatures haven’t fallen below 90 degrees Fahrenheit since early July, forecasters are predicting a 20th consecutive day with high temperatures over 110 degrees. This week, more than 44 million people in 28 U.S. states and several Canadian provinces have been affected by smoke from a record number of wildfires.