dew-point temperature

Yet only three variables showed a strong relationship with the 2015 die-off and similar events in 1988 and 1981: average maximum daily relative humidity, average minimum daily temperature and average maximum daily dew-point temperature.

It’s a ratio of dew-point temperature to air temperature.

The closer dew-point temperature gets to air temperature, the higher the relative humidity.

That reading is called the dew-point temperature.

Simply comparing the dew-point temperature to the air temperature outside the bulbs—as measured by a common weather thermometer, conveniently mounted on the hygrometer’s wooden post—gives the relative humidity.