On Monday, Phoenix reached a miserable milestone: It was the first time since 1974 that it had 18 days in a row of 110-degree or more temperatures. On Tuesday, it was poised to break that 49-year-old record and hit Day 19. The forecast called for a high of 115 degrees Fahrenheit.

People in the Southwest are used to brutal summers. Phoenix has had plenty of days that soar past 100 degrees. Water misters spritz patios, and neighborhoods and playgrounds clear out in the midday sun. Monsoons usually sweep through with refreshing relief. But this stagnant summer is testing even the hardiest, and putting many more people at risk.