Stratus
Usually thick, grey and covering large portions of the sky, stratus clouds are the harbingers of dreary overcast weather. The higher cirrostratus (above 18,000ft) contains ice crystals that bend rays of light to create a halo around the sun. If they turn the sky bright white it often means rain or snow within the next 24 hours. Mid-level altostratus (between 6,000 and 20,000ft) usually herald a storm, while the lumpy nimbostratus is a sign that somewhere down below is getting a good, steady dousing of rain.

Cirrus
Thin and wispy, these are the high-flyers in the cloud world, forming only above 18,000 feet where there is little water vapour present. They are blown into streamers known as ‘mares’ tails’ and usually point to fair weather. Cirrocumulus appear as small, rounded white puffs – either in isolation or in long rows when they resemble the scales of a fish, hence the term ‘mackerel sky’. Rows of cirrocumulus are your best bet for a dramatic sunset or sunrise.

Cumulus
These are the big bruisers. Cumulus clouds bubble up when water vapour condenses in upward air currents above the earth’s surface. They can tower from below 6,000ft to over 50,000ft. That’s a lot of cloud. And sometimes a lot of rain. When the atmosphere becomes unstable with very strong updrafts, cumulus clouds turn nasty and become cumulonimbus, better known as thunderstorms.