Relative Humidity…And Its Relative

Several days ago a cold front swept through our region. However, on the days prior, a warm, humid air mass was in place over the region. The weather felt amazing to me! However, a few people had yet to get acclimated to the conditions as I often overheard people talking about how humid the air was.

This got me thinking about some of the ways we measure moisture in the atmosphere and how some of these measurements are often misinterpreted.

So what is relative humidity and how should we interpret it? Relative humidity is a measure of the the amount of moisture in the air compared to what the maximum amount of moisture in the air could be. This means relative humidity is relative to the actual air temperature. Look at the graphic below; the amount of water vapor remains the same, but the relative humidity changes as the temperature changes.

Another way meteorologists measure moisture is by finding the dewpoint temperature. The dewpoint temperature is the temperature needed to cool the water out of the air. This is best shown by the formation of dew on summer mornings. Dew forms after the temperature drops below the dewpoint temperature.