What cloud is that?

We've got some pretty interesting names to describe what we see in the sky: lenticular, mammatus, asperitus, castellanus.

What Cloud is That, and does it mean it will rain?

Lets dissect, starting with the ten basic types.

Image from Geo for CXC

Image from Geo for CXC

Clouds are classified by how high up the base of the cloud is (low, mid and high) and what sort of shape they form (stratus or cumulus). This can tell us what kind of weather to expect.

Stratus are clouds in a layer, usually a grey, widespread sheet. Cumulus are the puffy, cauliflower-like, clumpy cloud, often with vertical development.

CUMULUS

Can range from 'fair-weather' cumulus (or if you want to be really weather nerdy: 'cu', like 'Q'), to great towering beasts of a cloud, extending well up into the atmosphere. 

They form with clear air around them, and move with the wind, so it goes from sunny to cloudy to sunny. If they have enough vertical development, the particles inside become too heavy, and rain falls out. So, we go from sunny, to downpour, back to sunny. 

If they grow enough, they become cumulonimbus, the thunderstorm cloud. 

A perfect example of cumulus clouds, growing enough to produce wet weather. One part is in a downpour, the rest are dry. Image from Australian Sky and Weather

A perfect example of cumulus clouds, growing enough to produce wet weather. One part is in a downpour, the rest are dry. Image from Australian Sky and Weather

STRATUS

Limited vertical development means less rain particles inside, so its usually associated with drizzle. 

But altostratus are beefier, and can be a sign of rain on the way, particularly associated with the huge cloudbands that come down from the tropics. When they develop into nimbostratus, it can be the favourite type of weather in agricultural areas: days of light to moderate, steady rain. 

Stratus or altostratus (depending on the elevation of this land), forming nimbostratus, with a hint of stratocumulus too. Image from skypix photography

Stratus or altostratus (depending on the elevation of this land), forming nimbostratus, with a hint of stratocumulus too. Image from skypix photography

COMBO CLOUDS

Clouds do like to get together, forming combinations of stratus and cumulus, keeping the properties of both genes. 

Stratocumulus (weather nerds pronounce as 'strato-cu') is often seen in Melbourne - our mostly cloudy days, with the odd drizzly shower underneath. Altocumulus altostratus ('ack as') is the mid level version of this, and let us take the rain parts of altostratus, and embed heavier showers inside to make even more rain. 

Stratocumulus as a grey sheet with lumpy bits - both genes coming together to create a fairly grey day. Photo by cloud-maven.com

Stratocumulus as a grey sheet with lumpy bits - both genes coming together to create a fairly grey day. Photo by cloud-maven.com

HIGH CLOUDS

Cirrus are the ones right at the top, not attached to any cloud below them. Made of ice crystals, they don't produce any wet weather. 

Cirrus are the wispy clouds, cirrocumulus are small and rippled (and look amazing at sunrise/sunset), and cirrostratus are sheets of the wispy cloud, forming halos around the sun and moon.

Cirrus won't rain on us, but they can let us know that rain is on the way. Winds are strongest at that cloud level, so they are pushed here first, before the rest of the cloud associated with the weather system. 

Cirrus cloud in Swifts Creek, Victoria. Photo by Fir0002/Flagstaffotos

Cirrus cloud in Swifts Creek, Victoria. Photo by Fir0002/Flagstaffotos

These are the ten basic types, but that's just skimming the surface. The variations on these are endless, ranging from cumulus humilis and cumulus mediocris (that don't sound very impressive) to altocumulus stratiformis translucidus undulatus!

Want more? See my Weather Resources page.