NASHVILLE, Tenn. (WKRN) — When you hear the News 2 Weather Authority team mention the phrase “clear and cool,” it’s not just a convenient description. It’s actually the result of the atmosphere’s interaction with our number one heat source: the sun!

The phenomenon that results in a “clear and cool” evening is called radiational cooling. 

How does radiational cooling work?

During the day, solar radiation heats up the Earth and the atmosphere. After the sun sets at night, daytime heat escapes the earth and begins to rise. From there, one of two scenarios can happen.

The first scenario happens when it’s cloudy outside. Clouds act as a blanket – keeping heat in- preventing it from rising into the upper levels of the atmosphere. With that heat trapped, temperatures have a harder time cooling down as much, or as quickly. 

In the second scenario, there’s a clear sky with no clouds in sight. When there are no clouds in the way, radiation gained from the sun can escape back into the upper levels of the atmosphere, and temperatures at surface cool down very quickly. 

A great example of this you can find im a desert climate, where a clear sky during the daytime will heat things up quickly, but a clear sky overnight lets heat escape allowing temperatures to cool. This is why there’s often a large difference between daytime highs and early morning lows in a desert.