Ask a Met: How the Moon Influences Weather — Tides, Pressure, and Myths

Ask a Met: How the Moon Influences the Weather

This week’s question comes from Morning Brief reader Noah: “How does the moon affect the weather?” Meteorologist Jonathan Belles explains that while the moon’s gravitational pull has a very noticeable effect on the oceans, its influence on the atmosphere is real but much smaller.

Tides beyond the ocean
We usually associate the moon with ocean tides, but the atmosphere experiences atmospheric tides as well. Even the solid Earth shows tiny deformations called terrestrial tides, where the crust bulges and flexes slightly as the moon orbits. All of these effects arise from gravity: the moon pulls on material nearest it, producing bulges in water, air and—very subtly—the solid Earth.

For a dramatic illustration of ocean tides, look at the Bay of Fundy, where the difference between low and high tide can be measured in feet. The size of tidal effects depends on geometry and distance: when the sun, moon and Earth align at new or full moon (a configuration that produces spring tides), tidal forces combine. When the moon is unusually near Earth (a supermoon, i.e., a perigee syzygy), tides tend to be higher than average.

So how does this affect weather?
Atmospheric bulges slightly change the distribution of air mass and therefore pressure. In places and times where the lunar-induced atmospheric bulge concentrates air vertically, local pressure can rise a little. Higher pressure generally suppresses cloud formation and precipitation, so the moon can have a measurable but very small effect on rainfall. These changes are far smaller than the normal daily and seasonal pressure swings driven by solar heating, jet streams, topography and ocean currents.

Myths and human behavior
Folk beliefs—like the idea that more babies are born during a full moon—have long circulated. Medical research has found no convincing evidence that the lunar phase changes birth rates. Personal anecdotes persist (Belles notes his mother says he was born at a full moon), and cultural stories about the full moon bringing out strange behavior remain common, but they are not supported by robust scientific data.

Bottom line: the moon does influence the atmosphere, but its effect on weather is modest and usually eclipsed by far stronger drivers such as sunlight, air masses and local geography. Careful instruments can detect lunar signals in pressure and precipitation records, but these signals are small.

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