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

A life-threatening heat wave has enveloped the East Coast, hitting cities with the worst of the high temperatures on Tuesday before relief moves in later in the week. This is the first major heat wave of the season,

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