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Image: Getty Images / Archi Banal
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ScienceDecember 23, 2022

Twelve classic clouds coming to a sky near you this summer

Image: Getty Images / Archi Banal
Image: Getty Images / Archi Banal

Be poetic and scientific this summer as you lie on your back in the long grass, pointing out the beauty of the clouds and also naming them accurately.

Next time you’re out and about, drag your eyes from your screen and look up for a change. What you see might surprise you.

Clouds are not just for geeks. Anyone who appreciates nature and the landscape can be wooed by the beauty of clouds and their fleeting moment in the sun.

They speak to the sensitive and artistic among us. More prosaically, they can also tell you if you’re about to get soaked.

It’s not for nothing that early Māori called our land Aotearoa, the land of the long white cloud. Sitting stubbornly between the sub-tropics and the sub-Antarctic, and thousands of kilometres from our nearest neighbour, Australia, we are blasted by westerly winds which whistle through every nook and cranny of our mountainous islands.

The clouds are the visible sign of that turbulence in our skies. But clouds are like people, and not just a bunch of water droplets or ice crystals flying in close formation. Each type has its own temperament, its own personality.

Clouds are classified as high, medium or low, depending on the height of their base above sea-level.

High clouds – cirrus, cirrocumulus and cirrostratus – are made of ice crystals and are generally between about 7,000m and 12,000m up.

Middle clouds – altocumulus, altostratus and nimbostratus – comprise ice crystals and water droplets and lie between 2,000m and 7,000m.

Low clouds – stratus, stratocumulus, cumulus and cumulonimbus – have bases between ground-level and about 2,000m. They are mostly composed of water droplets but cumulonimbus clouds, which produce thunderstorms, can reach to 12,000m or more and have ice crystals in them too.

Here’s a rough guide to 12 classic clouds you’ll see during the great Kiwi summer

Cirrus – “whimsical”: Nothing says lazy, hazy days of summer quite like these streaks of ice brush-stroked on a blue sky. Cirrus clouds usually accompany fine, settled weather, but may also indicate a frontal system is a day or two away or the presence of a jetstream, a ribbon of 200kmh-plus winds above 10,000m.

Cirrus flying high above Christchurch (Photo: Paul Gorman)

Cirrocumulus – “sensitive”: A honeycomb or lattice of ripply cirrocumulus is one of the rarest sights in the sky. These delicate blobs are often the highest clouds in our atmosphere and tend to show turbulent air – think driving over cobblestones. High altocumulus can look almost like cirrocumulus, but according to the British Cloud Appreciation Society the individual cloudlets in the latter cannot be bigger than the width of a finger held at arm’s length.

Cirrocumulus honeycombs over Wellington, a rare sight. (Photo: Paul Gorman)

Cirrostratus – “ethereal”: This featureless veil of ice brings us spectacular halo phenomena, the result of the way the cloud’s crystals refract sunlight. It is often thin enough to allow the sun to cast weak shadows, but generally signifies the approach of a warm front and tells us rain can be expected within 24 hours.

An icy veil of cirrostratus draws a halo around the sun. (Photo: Paul Gorman)

Altostratus – “gloomy”: Cirrostratus can grow up to be altostratus if conditions allow the cloud to thicken and lower as a front gets closer. A drab sheet of altostratus presents an increasingly depressing appearance, even if the sun can still just be seen through it, as if through “ground glass or frost”, according to the appreciation society. Rain or snow may already be falling lightly, or not far off.

A lowering grey layer of altostratus starts blocking out the sun. (Photo: Paul Gorman)

Altocumulus – “flashy”: One of the biggest show-offs in the sky, altocumulus can take a variety of forms and is often at its most garish at sunrise and sunset. Its presence often indicates patches of rough air or buoyancy in the middle layers of the atmosphere, due to weather systems or mountains below, and can be an early predictor of thunderstorms.

Altocumulus clouds often make the best sunrises and sunsets. (Photo: Paul Gorman)

Altocumulus lenticularis – “alien”: New Zealand skies rock when it comes to lenticulars, those strange lens, almond or UFO-shaped clouds which develop in bouncing layers of air downwind from the main ranges. When they join together, they form the incredible nor’west arch seen in the east of both islands.

The other-worldly swirls and saucers of altocumulus lenticular clouds over Canterbury at sunrise. (Photo: Paul Gorman)

Mammatus and virga – “apocalyptic”: If the atmosphere could have a smacking hangover, this is what it might look like, with patches of swirling melting and evaporating ice crystals – “virga” – caught up in downdraughts, and large breast-like protuberances called “mammatus”. Often seen on the underside of a nor’west arch or below a thundercloud.

A show-stopping sky of mammatus (breast-like) and virga (streaks) clouds (Photo: Paul Gorman)

Nimbostratus – “weepy”: The most depressing and cheerless of clouds, and actually difficult to see due to the steady rain or snow falling from it. If you’re under it, the best thing you can say is the weather probably won’t get any worse.

A featureless gloomy layer of rain-bearing nimbostratus. (Photo: Paul Gorman)

Stratus – “scruffy”: Stratus is basically fog that isn’t on the ground. These patches of ragged, quickly churning grey form below other clouds and are the ones most likely to delay your plane.

Stratus is the lowest of all the clouds and can easily turn into fog if it lowers to the ground. (Photo: Paul Gorman)

Stratocumulus – “old faithful”: Not many days go by without seeing this lower version of altocumulus. It often marks the top of inversions, in which the temperature unusually rises with height rather than falls, and burns off quickly in strong sunlight. In winter, however, it can hang around for days in dismal anticyclonic gloom.

Stratocumulus cells on a winter’s morning. (Photo: Paul Gorman)

Cumulus – “jolly”: These cotton-wool like, bubbly clouds are the perfect accompaniment to summer. As the sun heats the ground the air rises and condenses, forming the tell-tale flat bases and dazzling white cauliflower heads. Cold air blowing over warmer seas does the same. If cumulus clouds get too big, watch out for what might happen next…

Puffy cumulus clouds sprouting in cold air at St Clair, Dunedin. (Photo: Paul Gorman)

Cumulonimbus – “the boss”: Growing out of cumulus, with massive columns rising as much as 10,000m into the sky and topped with icy anvil tops, these show-stoppers are numero uno in the cloud world. Angry and unpredictable, they can bring damaging hail, squalls and tornadoes, along with ear-splitting thunder, blinding lightning and torrential rain. Never underestimate how dangerous cumulonimbus clouds can be.

A thunderstorm-bearing cumulonimbus cloud wearing its tell-tale icy anvil offshore of Westport. (Photo: Paul Gorman)
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