A Sky Full of Signs: How We Understand The Weather

A sky filled with clouds is more than a collection of shapes. Long before weather forecasts appeared on television screens or smartphone apps, people looked upward for answers.  And even now, when forecasts get it wrong, the sky still gets it right. A clear sky lets us know it's going to be a warm day, while a sky filled with grey clouds might make us leave home with an umbrella. Our understanding of weather didn't appear out of thin air. People noticed and adapted. We say we feel under the weather when we are ill, but there was a time when all we could do was literally be under the weather and look at the sky to understand how the rest of the day would go.

 

In Vedic India, farmers tracked constellations to predict the arrival of monsoons. While Polynesians noted cloud formation and bird migration to ensure smooth weather during wayfinding. Other cultures followed their systems of weather forecasting; no fancy equipment. Just observing what was happening up in the sky. This has led to many beliefs and sayings about what the visual cue means in meteorology. “When the dew is on the grass, rain will never come to pass” reminds us about how dew is formed when the sky is clear. Hence, seeing dewdrops means there were no rain clouds at night and that it wouldn’t rain soon. Another rain-predicting phrase is “rainbow in the morning, shepherds take warning; rainbow in the night, shepherds delight”. The weather typically moves from the west to the east. If you see a rainbow in the morning, it means rain is on the way; if you see it at night, the rain has already passed, and the weather will be delightful. Both sayings are not fully scientifically accurate, but observationally likely. In 340 BCE, Aristotle put his own spin on meteorology in his comprehensive treatise, Meteorologica. It had two main theories: the universe is spherical and the four-element theory. This wasn’t just Greek theories but also findings by poets, philosophers and historians. Though many theories were proven wrong, Meteorologica is the core foundation of modern meteorology.

 

Aristotle's diagram of the winds and their directions

A cloud-watching club isn’t just for admiring the shapes condensation can make; it can also help with predicting the weather soon. Clouds can speak. We all know the greyer the cloud, the more likely it is to rain, but there's so much more that clouds tell us. Clouds can block, absorb, and alter how the sun's rays reach the Earth, influencing temperature. It plays a big role in distributing heat from the equator to the poles. Satellite cloud imagery helps tell us how accurate weather forecasts really are. French naturalist Lamarck first introduced the idea of cloud classification, but the Essay on the Modification of Clouds by Luke Howard popularised it. There came a cloud observing system. The book introduced a Latin-based system with five Latin words that do all the heavy lifting. Cirro refers to a lock of hair and refers to a high-level cloud, while Alto refers to mid-level clouds. Strato means a layer, and Cumulo a heap. Nimbo refers to rain; it isn’t exclusive to rainclouds and describes every cloud with a chance of precipitation.

 

Cloud formations illustrated in Luke Howard's Essay on the Modification of Clouds

There are many types of clouds, but they mostly stem from the four main kinds:

• Cirrus: Meaning “curl” or “lock of hair”, have a feathery and thin appearance. It is commonly mistaken for a contrail of a passing aircraft. It is a high-level cloud made entirely of ice crystals. They often indicate fair, warm weather, with a warning that it may change soon.

 

• Cumulus: Meaning “heap”, is the cloud we drew growing up with a bunch of rounded curves on the top and a relatively flat base. It is made up of either ice crystals or water droplets, or both.  It is a mid-level cloud and is associated with fair weather. However, bigger cumulus clouds do hint at potential storms.

 

• Stratus: Meaning “layer”, looks like a blanket across the sky. It is found at a low level in the sky, which is mostly made of water droplets. Since it covers a lot of the sunrays, the weather is cool, but there is an overcast chance of a drizzle.

 

• Nimbus: Meaning “rain cloud”, are mostly dark. Unlike the other main clouds, there is no such thing as the Nimbus cloud since it is always combined with other clouds, such as the nimbostratus and cumulonimbus. It is another low-level cloud. It is moisture-filled and associated with precipitation such as rain or snow.

 

By the end of the Renaissance era, there was a need for machines. Farmers and travellers needed something more concrete than old folklore or cloud shapes. In the mid-15th century, Nicholas Cusa invented the hygrometer, an instrument used to measure air humidity. In 1592, Galileo Galilei invented the thermometer. And in 1643, Evangelista Torricelli invented the barometer, a tool for measuring atmospheric pressure. Many more inventions further enhanced meteorology. With the help of telegraphs, it became a weather-forecasting channel accessible to everyone. Weather observations from different locations could suddenly be shared almost instantly, allowing meteorologists to create weather maps and track the movement of storms across large areas. Today, weather forecasting combines observations from weather stations, radar systems, weather balloons, and satellites, as well as computer models. Though not perfect, it doesn’t require hypervigilance or local observations to track.

 

a meterological office

Every cloud, breeze, and shift in the atmosphere tells a story. The weather is never unpredictable; it is just that we didn’t know what the signs were telling us.