Some hot days feel even worse thanks to high humidity, trapped heat and dew points. Cities are especially vulnerable. By Nazaneen Ghaffar Nazaneen Ghaffar is a reporter on The Times’s weather team. It ...

Relative humidity measures how much moisture is in the air compared to how much it could hold at a given temperature. It is simply the dew point temperature divided by the air temperature, times 100.

Every summer, I get asked this question: "Why don't you use relative humidity? I don't care about the dew point." The thing is - you should care about the dew point more. The dew point is quite ...