Tens of millions of Americans sweltered outside or sought air-conditioned refuge as an "extremely dangerous" heat wave blanketed the eastern United States on Tuesday with record high temperatures.

The heatwave continues, with nearly half of the U.S. population now under a heat advisory, and triple-digit temperatures being felt as far north as Maine.

Extreme heat is impacting states across the country. See maps of high temperature forecasts and heat index levels.

Extreme heat is impacting states across the country. See maps of high temperature forecasts and heat index levels.

Humidity will soon surge to extreme levels across 40 states. Find out where there will be excessive heat and humidity — and how humidity patterns are changing.

Scientists say 4 billion people, about half the world's population, experienced at least one extra month of extreme heat because of human-caused climate change from May 2024 to May 2025.

Scientists say 4 billion people, about half the world’s population, experienced at least one extra month of extreme heat because of human-caused climate change from May 2024 to May 2025.