As the temperature-dew point spread decreases, what happens to relative humidity?

When the temperature-dew point spread decreases, the relative humidity increases. This phenomenon occurs because the dew point represents the temperature at which air becomes saturated with moisture, leading to condensation. As the air temperature drops or the dew point rises, the air becomes closer to saturation.

Relative humidity is a measure of how much moisture is present in the air compared to the maximum amount of moisture air can hold at that specific temperature. When the spread between temperature and dew point is small, the air temperature is nearing the dew point, indicating that the air is nearly saturated with moisture. As saturation increases, so does the relative humidity percentage, meaning that more moisture is present relative to what the air can hold. Thus, a decrease in the temperature-dew point spread signifies an increase in relative humidity.