Extreme levels of heat and humidity are forecast to spread across the country over the next two weeks, blanketing the Southwest, Midwest, and East Coast with high temperatures beginning this June 19 ...

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.

Extreme heat waves can cause cases of dehydration, exhaustion, heat stroke and even death. But the air temperature isn't the only factor in how dangerous a hot day is; there's also another measure, ...