Ask A Met: How Does The Moon Affect The Weather?

This week's question comes from Morning Brief reader Noah, who asks, "How does the moon affect the weather?"

Meteorologist Jonathan Belles: Well, the big caveat is that the moon affects the ocean much more than it does the atmosphere.

We often think of ocean tides, but we also have atmospheric tides. In fact, even rocks have tides, which I didn't know until recently. We call them terrestrial tides, which describes the way the Earth’s crust bulges or flexes with the orbit of the moon.

Obviously, though, those movements are much, much smaller than you might recognize with an ocean tide.

It's just gravity, one body pulling everything – tides, rocks, the atmosphere – towards the bigger object. As the moon goes around the Earth, you get this bulge, both in the atmosphere and the ocean, closer to the moon.

Look at the Bay of Fundy, if you need an example, where water levels are many feet higher during high tide.

This effect is also based on how close the moon is to the Earth, because closer objects have more pull. We see higher tides at new moon and full moon than we do at first and last moon because at full moon and new moon, the sun, the moon, and the earth are aligned.

But that bulge in the atmosphere also affects the weather. Last week, we talked about light hitting particles in the atmosphere. When those particles stack up vertically in an atmospheric bulge, that creates pressure because those particles weigh something, right?

Well, higher pressure means less rainfall. It is a very small effect, but it is measurable.

There’s also an old wives' tale that suggests more babies are born during a full moon. I guess the idea is that a change in pressure makes giving birth easier.

Doctors dispute this and there really is no evidence for it. But my mom will tell you that I was born early during a full moon.

Now, I think it is more common to say that when the full moon comes out, the crazy people come out, too. That’s how I feel about it: the crazy person came out.

Do you have a question to ask the meteorologists at Weather.com? Write to us at [email protected] and we’ll pick a new question each week from readers to answer.