Weather Tidbits: Dewpoint Temperatures

This edition of Weather Tidbits will be discussing dewpoint temperatures. Dewpoint temperatures are referenced frequently when communicating how muggy and humid it feels outside. The dewpoint temperature is the temperature that the air needs to cool down to at constant pressure to reach full saturation. When the air is fully saturated, the relative humidity is 100%. The relative humidity is the measure of the amount of water vapor in the air compared to the amount of water vapor that the air can hold at the current temperature. This is derived by dividing the dewpoint by air temperature and multiplying that answer by 100. Dewpoints are a good indicator of how much moisture is in the atmosphere. The higher the dewpoint, the higher the air’s moisture content.

Relative humidity is not an accurate parameter to use when communicating how humid it feels outside. A 50 degree day with a 48 degree dewpoint and thus a 96% relative humidity is not going to feel as uncomfortable as an 85 degree day with a 70 degree dewpoint and thus an 82% relative humidity. Using dewpoint on its own is the way to go. A universal scale for dewpoints is used when determining the comfort level of the air. Dewpoints below 60 degrees are considered comfortable. Dewpoints between 60–70 degrees will feature a noticeable mugginess to the air. When dewpoints rise above 70 degrees, that is when it starts to feel very humid and uncomfortable outside.