Cloudy and Cool

I’ll take a stab at it, Rube! But it’s more than what I normally tackle in a comment.

First, as you know, the wind does not always diminish at night. Think of a winter storm or hurricane–it’s as windy at night as during the day in those situations. However, the wind does diminish significantly at sunset in many calmer weather situations.

The diminishing wind scenario often happens following a sunny day. During the day, the sunshine heats the ground, and, in turn, the ground heats the air right above the ground. Since warm air is lighter than the cooler air above it, this sun-warmed air rises. In many cases, the atmosphere is stirred up enough by this heating process alone to result in a breezy day that turns calm when the ground-warming sun sets.

In many cases, it’s that simple…but…I’ll give you more infomation in case you’re interested in a more complete picture. I promise that I still won’t talk about “energy” and “dynamics,” though.

This process can be more dramatic than just creating a breeze, though. It can be a very windy day that becomes virtually calm at night.

Air is like water in a sense. When water near the heat source at the bottom of the pan rises, relatively cool water from the top of the pan sinks to replace it. Similarly, when sun-warmed air rises into an atmosphere where it’s windy aloft, the compensating sinking air elsewhere can pull some of the higher winds down to the ground with it. It’s not always that simple since there are other competing forces at work, but that’s a big part of it. As the process stops (when the sun sets), the wind doesn’t translate to the surface as effectively–and it becomes much calmer.

The weather is not always easy to explain, which is probably why you’ve never gotten a simple ansower. But, I hope this helps!

(On a side note, an exaggerated version of wind being pulled down from higher elevations is what can cause a 70- or 80-mph wind gust wind a thunderstorm–powerful upper-level winds are pulled to the ground by the thunderstorm–and that can happen during the day or night.)