We’ve all been hoping for clear skies, free of cloud cover for the August 21st solar eclipse so we can get a good view of the Moon pass in front of the Sun. But do eclipses themselves have any impact on our weather?
When a solar eclipse occurs, the Sun, Moon, and Earth are in precise alignment; so precise that the Moon will cover the entire disc of the Sun and completely blot out its rays (for those in the path of totality). Solar eclipses not only mimic nighttime by turning the sky dark, they also bring evening’s cooler air temperatures.
If you’re standing outdoors on August 21st, when the total solar eclipse occurs across the U.S., you’ll feel this firsthand.
As the eclipse begins, temperatures will dip gradually at first and then fall steadily as “totality” — the period when the Moon completely covers the Sun — occurs. During the 2-3 minute period of totality, temperatures bottom out, reaching their lowest. (After totality ends, air temperatures will slowly warm again if sunset hasn’t yet occurred.)
Solar eclipse cool-downs aren’t unlike cool downs that occur daily between midday and sunset. However, instead of temperatures cooling because the Sun has set, the air cools because the Moon covers 100% of the Sun’s disk and temporarily blocks sunlight. This cooling is faster too, occurring over a period of minutes rather than the hours it ordinarily takes.
How much of a temperature drop can we expect?
According to the National Aeronautics and Space Administration (NASA), air temperatures during a solar eclipse cool by about 10-15 degrees Fahrenheit. Of course, this can vary based on location and season. For example, during the total solar eclipse of 1834 (another eclipse that was visible in the U.S.), temperatures reportedly cooled by as much as 28° F!
Solar eclipses have another effect on weather, too: they cause winds to slow and change direction.
As the Sun heats the Earth, it creates “hot spots,” or places where the ground warms hotter than other ground nearby. Because hot air is “lighter” or less dense than cooler air, it rises and lowers air pressure over these hot spot areas. The cooler nearby ground has higher pressure from the more dense air located there. It’s a weather rule-of-thumb that air moves from areas of high pressure to areas of low pressure. So, air rushes from the cooler patches to the “hot spots” in an attempt to equal out these two extremes. This movement of air is what we call wind.
However, during an eclipse, these hot spots don’t get as hot because there isn’t as much sunlight heating them. Without the Sun’s extreme heating, point A doesn’t get much hotter than point B. Since both locations are relatively equal in temperature (and pressure), the air won’t rush as fast between them, and winds won’t blow quite as hard.
What if you’re outside of the path of totality?
Since some of the Sun’s light will still be blocked, you’ll feel air temperatures drop, but only slightly. Be sure to consult our eclipse map to check what percent of the Sun will be visible for your city. Even if you’re outside the path of totality, you may still feel a noticeable cooling. However, if your location will only see 50% or less of the Moon cover the Sun at peak time, the weather will likely only cool by a degree or two.