Why Nighttime Is Just as Dangerous as Daytime During a Heat Wave

The meteorological summer so far—June and July—is on track to be the fifth warmest on record for the continental U.S., and as August gets fully underway, the Northeast is already in the grip of another killer heat wave, with heat indexes that could break 100 F this weekend. Even during the hottest days, though, city dwellers usually get a natural break from the heat when the sweltering sun disappears to make way for the relatively cool night.