Humidity, Heat Index, and Why Houston Feels Hotter Than Phoenix

A 95°F day in Houston at 70% humidity has a heat index around 110°F. The same 95°F day in Phoenix at 20% humidity feels more like 92°F — actually slightly cooler than the thermometer.

Heat index accounts for the fact that sweat can't evaporate efficiently in humid air, so your body's cooling system fails. That's why the Gulf Coast produces more heat-related emergency room visits per capita than the desert Southwest, despite lower peak temperatures.

The practical takeaway: when comparing summer climates, don't just compare highs. A city's dewpoint and evening lows together determine whether summer is merely warm or genuinely dangerous.