Cumulus Clouds

Cumulus

The cotton wool tufts that form on a sunny day.
Leonardo da Vinci once described clouds as 'bodies without surface', and you can see what he meant. They are ghostlike, ephemeral, nebulous: you can see their shapes, yet it's hard to say where their forms begin and end.
But the Cumulus cloud is one that challenges da Vinci's description. Rising in brilliant-white cauliflower mounds, it looks more solid and crisply defined than other cloud types. As a child, I was convinced that men with long ladders harvested cotton wool from these clouds. They look as if you just could reach up and touch them – and, if you did, they would feel like the softest things imaginable. The most familiar and 'tangible' of the cloud family, this is a good type for budding cloudspotters to cut their teeth on. Cumulus is the Latin word for 'heap', which is simply to say that these clouds have a clumpy, stacked shape. The people who concern themselves with such things divide them into humilis, mediocris and congestus formations – these are known as 'species' of Cumulus. Humilis, meaning humble in Latin, are the smallest, being wider than they are tall; mediocris are as tall as they are wide, and congestus are taller still.
It is the smaller ones that generally start forming over land on sunny mornings. And because neither they nor their mediocris brothers produce any precipitation, they are widely recognised as 'fair-weather clouds' – a pair of puffy fingers up at those who can only think of clouds as the opposite of fine weather. A sunny afternoon below the drifting candyfloss curls of the Cumulus is far finer than the flat monotony of a cloudless sky. Don't be brainwashed by the Sun fascists – fair-weather Cumulus have a starring role in the perfect summer's day.
There is one other species of this cloud: Cumulus fractus. This has a much less puffy shape, its edges being fainter and more ragged. It is the way a Cumulus looks when it is decaying at the ripe old age of ten minutes or so. Besides being divided into species, each of the ten main cloud types – each 'genus' of cloud – has a number of possible 'varieties'. These are characteristics of appearance that are often observed in that cloud type. For the Cumulus cloud, the only recognised variety is Cumulus radiatus, which is when the clouds are lined up in files parallel to the wind. These rows of cotton wool tufts are sometimes called 'cloud streets'.
Although Cumulus is generally associated with fine weather, any cloud can under certain conditions develop into a rain-bearing formation and Cumulus is no exception. The innocuous Cumulus humilis and mediocris can on occasions grow into the angry, towering Cumulus congestus, which it must be said is anything but a fair-weather cloud. It is well on the way to becoming the enormous awe-inspiring Cumulonimbus thundercloud, and can itself produce moderate to heavy showers. Whilst the development of Cumulus clouds from humilis right up to the congestus and beyond can be a daily occurrence in the hot, humid tropics, it is less common in temperate climes. Nevertheless, if you see Cumulus develop into the tall congestus stage before midday, there is a distinct possibility of heavy showers by the afternoon.
Attention all cloudspotters: 'In the morning mountains, in the afternoon fountains.'

THE DISTINCTIVE SHAPES of Cumulus clouds may go some way to explaining why they are the cloud of choice in the drawings of young children. No six-year-old's picture of a family in front of their house feels complete without a few puffy Cumulus floating in the sky above. Children just have a fascination with clouds. Can it be that, wheeled around in prams staring up at the sky as infants, they develop a deep connection with the clouds – like young chicks forming a familial bond with the first thing they see out of the egg? Who knows? Their drawings may show people with arms coming out of their necks, whose eyes aren't even attached to their faces, but young children seem to capture the organic shapes of Cumulus clouds pretty well. No doubt they are just easier to draw than other types. Perhaps, however, their ubiquity in junior school drawings is due to something more fundamental than this. Cumulus also feel like the most generic and basic of all the varieties. Picture a cloud in your mind and it is likely to have the shape of a Cumulus, which is probably why it was their gentle, bulging curves that were used by Mark Allen, a 22-year-old graphic designer, when he created the icons for the BBC weather forecasts in 1975. Back then they were in the form of rubber-coated magnets, which the TV forecasters would slap on to the map of Britain. I'd snigger, along with the rest of the nation, each time these fell to the ground after they turned their backs.

The Cumulus symbols were used to stand for cloud cover for thirty years until 2005, when the BBC weather graphics were completely redesigned into a dynamic 3D system, which showed how cloud coverage and rainfall distribution varied in real time. Whilst the new system gave a much more accurate indication of cloud cover, viewers complained that the way the camera panned and swooped across the computer-generated map made them feel sick. Perhaps, like me, they were really just sad to see the friendly Cumulus symbols disappear.