A scorching heat wave now engulfs most of the country. Thousands live under excessive heat warnings as temperatures soar past triple digits in many states. Washington, D.C. expects tie new records this week. New York City turned libraries and subway stations into sanctuaries for Fourth of July visitors. The city now warns of dangerous highs too . The National Weather Service extended warnings from the Midwest down to the East Coast.
Medical professionals advise heat exhaustion and dehydration may turn deadly fast . Cities opened extra rec centers and malls for relief . Forecasters see little change through the coming days .