Millions of people across the eastern United States are experiencing the “first significant heat wave this season” over the next several days as record-high temperatures set in, according to the National Weather Service.

An extremely dangerous heat wave is underway for the eastern half of the United States as a potent heat dome reaches its peak, bringing the hottest temperatures of the year so far – the hottest in years for some cities – and putting tens of millions at risk.

The entire eastern half of the United States will experience above-average temperatures this week as a massive heat dome descends, impacting 147 million Americans. Until at least Thursday, 28 U.S. states from Texas to Maine will experience moderate to extreme heat waves,