A major heat wave is set to engulf much of the United States this week, with over 230 million people facing dangerous, record-setting temperatures as a heat dome settles over the East and Midwest. As the holiday approaches, cities like New York and Boston are bracing for heat indexes reaching up to 110 degrees. Authorities have issued extreme heat warnings and advisories, with more than 200 million under heat alerts. Residents are being reminded to stay cool and seek relief from the oppressive heat, as temperatures are expected to soar to historic levels. Meanwhile, the West is experiencing unseasonably cooler temps, contrasting with the extreme conditions anticipated in the East. The National Weather Service is advising heightened awareness and preparations as this dangerous weather system unfolds.