"It's a Dry Heat" Is Wrong. The Systems That Communicate Your Risk Still Say Otherwise.

Phoenix's 2023 heat wave was the driest of six deadly events the Perkins-Kirkpatrick study examined. It was equally lethal. The killing mechanism is different from humid heat but no less efficient: sweat evaporates so fast you don't register how much fluid you're losing. The feeling of relative comfort is the hazard.

And the primary tool Americans use to gauge danger makes it worse. At 115°F with 8% humidity, the heat index reads 108. The instrument designed to warn you tells you the heat feels cooler than it actually is.