Eastern U.S. heat dome brings dangerous conditions to millions during July Fourth weekend

A powerful heat dome pushed dangerous temperatures across the eastern United States during the July 4th holiday weekend. Weather forecasters warned that the "heat index," which measures how hot the air actually feels when humidity is included, would reach extreme levels in many eastern cities. Philadelphia was expected to hit a heat index of 101°F on Saturday, July 4th. Remarkably, several eastern locations were forecast to feel as hot as, or even hotter than, Death Valley in California, which was itself expected to reach 102°F. The National Oceanic and Atmospheric Administration described the risk level as "major-to-extreme" across much of the eastern half of the country. Death Valley holds the world record for the highest air temperature ever measured, 134°F, set back in 1913.