The shape is the instrument reading. Here are seventeen.
1. The Fluffy White Heap With a Flat Base
Cumulus forms where warm ground heats a bubble of air until it rises, cools and reaches the height at which its moisture condenses.
The flat bottom is that height, which is why every cumulus in a sky has its base at the same level.
Like our content? Follow us for more.
2. The Same Heap, Grown Enormous
Cumulus congestus is a heap that has kept rising, towering upward with hard cauliflower edges and a darkening base.
It is a shower deciding whether to become a storm.
3. The One With the Flattened Top
Cumulonimbus has risen until it hit a ceiling it cannot pass, and spread sideways into an anvil.
That ceiling is the tropopause, and the anvil means the cloud has gone as high as the atmosphere allows.
4. The Thin White Streaks Very High Up
Cirrus sits so high that it is made entirely of ice crystals, drawn into strands by winds at that altitude.
The hooks on the ends show the crystals falling and being dragged sideways by different wind speeds.
5. The Milky Veil That Puts a Ring Round the Sun
Cirrostratus is a thin ice sheet covering the whole sky, thin enough that shadows still form.
The halo is sunlight bent through hexagonal ice crystals, and this layer often arrives a day before rain.
6. The Small Ripples in Rows
Cirrocumulus is high ice cloud broken into tiny regular grains, the classic mackerel pattern.
Regular spacing means convection in a thin layer, each cell the same size as its neighbours.
7. The Grey Blanket With No Features
Stratus is a featureless low sheet, often dull and flat from horizon to horizon.
It forms by gentle lifting or cooling rather than by rising bubbles, so there is nothing to see in it.
8. Fog, Which Is the Same Thing on the Ground
Fog is stratus that formed at ground level, usually because the ground cooled overnight and chilled the air touching it.
It is not a different phenomenon. It is a cloud you are standing inside.
9. The Thick Grey One That Rains All Day
Nimbostratus is deep, dark, shapeless and precipitating steadily rather than in bursts.
Steady rain means a wide slow lift, not a violent one, which is why it lasts for hours.
10. The Lumpy Grey Layer With Gaps
Stratocumulus is a low sheet broken into rolls or patches, with lighter gaps between them.
It is the most common cloud on Earth and it usually means dull but dry.
11. The Grey-and-White Patchwork at Middle Height
Altocumulus is mid-level cloud in rounded masses, larger than the high ripples and often with shading on one side.
Shading is the clue to height, since a cloud thick enough to cast shadow on itself is made of water rather than ice.
12. The Uniform Grey Sheet You Can Just See the Sun Through
Altostratus covers the sky at middle height and the sun appears as a bright patch, as if behind frosted glass.
This is frequently nimbostratus arriving, thickening and lowering as a front approaches.
13. The Lens Shape That Sits Still Over a Hill
Lenticular cloud forms in a standing wave downwind of high ground, where air lifted over the obstacle oscillates.
The cloud looks stationary while the air is rushing through it, condensing at the crest and evaporating beyond.
14. The Cloud That Forms Under the Cloud
Ragged scud hangs below a raining cloud base, formed in air moistened by falling rain rather than by lifting.
It is not part of the main cloud and it moves differently, which is what makes it look so unsettling.
15. The Long Roll Ahead of a Storm
A shelf or roll cloud forms along the leading edge of a storm’s outflow, where cold air spreading out lifts warm air ahead of it.
Its arrival is the visible boundary of the wind change rather than the rain itself.
16. The Streaks That Never Reach the Ground
Virga is precipitation falling from a cloud and evaporating on the way down, leaving trailing wisps beneath.
It means dry air below the cloud, and the evaporation cools that air enough to drive it downward.
17. The Bubbly Underside That Looks Wrong
Mammatus are pouches hanging beneath a spreading anvil, formed by cold cloudy air sinking into clearer air below.
They form on a dissipating storm rather than an arriving one, and they usually mean the worst has passed over.
Shape, Height and What the Air Is Doing
Flat bases marking the condensation level, heaps meaning rising air and sheets meaning stable air, ice at the top and water below, anvils hitting a ceiling and streaks that evaporate before landing.
The first item contains the whole system in miniature. Every heaped cloud in a sky has its base at exactly the same height because that height is where rising air has cooled enough for its moisture to condense – so a flat-bottomed sky is showing you a single invisible line in the atmosphere, drawn in cloud.
Like our content? Follow us for more.
