Dew point is the temperature at which water vapor in the air begins to condense into liquid droplets. When air cools down to its dew point, moisture that was invisible suddenly becomes visible as dew on grass, fog in the air, or condensation on a cold glass of lemonade.

Here's how it works: warm air can hold more water vapor than cold air, like how a large sponge holds more water than a small one. As air cools, it loses its ability to hold moisture. When it reaches the dew point temperature, the excess water vapor has nowhere to go, so it condenses into tiny droplets.

On summer mornings, you often see dew on grass because the ground cooled overnight until it reached the dew point, causing water vapor to condense. When you take a cold drink outside on a humid day, the air around the glass cools to its dew point, and water droplets form on the outside.

Meteorologists pay close attention to dew point because it helps them describe how humid the air feels. A dew point above 65°F feels muggy and uncomfortable. Below 50°F feels dry and pleasant. Dew point also helps predict fog, frost, and whether rain clouds might form.