A long-lasting extreme heat wave reached its dangerous crescendo Tuesday, bringing the hottest day in a decade to some major East Coast cities and putting millions of already fatigued Americans at risk.

Large swaths of the country were broiling under a heat dome, worsened by a humid atmosphere that’s circling the East.

Temps are soaring in cities across the Atlantic coast, where some cities are reaching 100 degrees with heat indexes approaching 110 degrees.