How can relative humidity be low, yet it still feels uncomfortable?
The old adage is, “It’s not the heat, it’s the humidity.” However, sometimes it is just plain hot. Relative humidity is just a measure of the amount of water vapor actually in the air compared to the amount of water vapor that could be in the air at a given temperature and pressure. Since warm air has a greater capacity for water vapor, desert climates with dry air can have single-digit relative humidities since the air is very far away from reaching saturation. While it is a “dry” heat, 120°F in Death Valley is still hot. There’s plenty more about humidity on this USA TODAY resource page.