Everyone complains about the weather, the old line goes, but nobody ever does anything about it, except try to predict it and arrange our lives around the forecast. Along the way, we've picked up ideas about the weather that don't quite hold up. From cold weather making you sick to red skies in the morning, here are some common beliefs about the weather that aren't entirely true.
Cold weather doesn't cause colds
You've heard someone say it, or maybe you've said it yourself: "Put on a jacket — you'll catch a cold." The problem is that cold weather doesn't directly cause colds.
Manal Mohammed, a microbiology lecturer at the University of Westminster, wrote about this for The Conversation. "Cold temperatures do not cause infections by themselves," she concludes. "Instead, they shape the biological, environmental and social conditions that allow respiratory viruses to thrive."
People spend more time indoors during cold weather, often in heated spaces with low humidity that dry out nasal passages, making it easier to catch a virus. There are physiological factors too, according to Mohammed: "Breathing in cold air lowers the temperature inside the nose and airways, which can trigger vasoconstriction [the narrowing of blood vessels]." This can weaken local immune defenses in the nose and airways, but that's not the same as a direct causal link.
So, while it's true that you're more likely to catch a cold or the flu during the winter, that isn't directly caused by your failure to wear a jacket. It's the viruses, not the temperature, that make you sick.
Lightning can strike the same place twice
"Lightning hitting the same place twice" is shorthand for something unlikely. But is it accurate? Kind of: it's true that, all things being equal, lightning rarely strikes the same place twice. But all things aren't equal.
Lightning tends to hit the highest nearby object, and in big cities this means the largest buildings are hit frequently: New York City's Empire State Building is hit, on average, 25 times per year, according to New York City Emergency Management. So lightning not only can hit the same place twice, but does so pretty often, although, according to NOAA, it doesn't always hit the highest point, so there's still truth to the idea that lightning is hard to predict.
Red skies really can predict the weather
You've heard it: "Red sky at night, sailor's delight; red sky in the morning, sailors take warning." The idea is old, and it has been part of sailing tradition for centuries. But is there any science behind this?
Yes, it turns out, but it doesn't work everywhere. First: what causes red skies? "A red sky appears when dust and small particles are trapped in the atmosphere by high pressure," according to the UK Met Office. "This scatters blue light, leaving only red light to give the sky its notable appearance."
A red sky means there's high pressure between you and the sun, and since the sun sets in the west and rises in the east, a red sky at night points to high pressure in the west, while a red sky in the morning points to high pressure in the east. But why does that predict the weather? In the mid-latitudes, the wind generally blows from the west, a pattern known as the prevailing westerlies, and high pressure means stable, dry weather; so a red sky at night means that stable weather to your west is about to be carried toward you, while a red sky in the morning means the high pressure is already to your east and moving away.
That only works, though, in the mid-latitudes, where the prevailing westerlies are the norm, roughly the band between 30 and 60 degrees in both hemispheres. In the tropics, by contrast, weather tends to build up locally rather than arriving from upwind, so sunrise and sunset colors aren't as useful for predicting it.
So this isn't entirely a myth: there's truth to the saying. It just doesn't work everywhere on Earth.