Navigation

UK Extremes

High Temp
17.2° C
Charlwood
Low Temp
-1.5° C
Cairngorm
Precipitation
16.0 mm
Achnagart
Wind Gust
93.2 mph
Aonach Mor

Cloud Spotting Guide

Clouds tell a weather story before the forecast catches up with it — a thickening veil of cirrostratus a day ahead of rain, or a sky full of harmless fair-weather cumulus that will burn off by lunchtime. This guide covers the ten basic cloud types recognised worldwide under the World Meteorological Organization's International Cloud Atlas, grouped by the height band they're normally found in.

Typical Height Range by Cloud Type

Approximate base-to-top height ranges above the UK. Cumulonimbus is the exception — a single storm cloud can span the entire atmosphere from low cloud base to the tropopause.

Show:

High-Level Clouds — roughly 6,500m (20,000ft) and above

Thin and pale, almost always made of ice crystals rather than water droplets because of how cold it is at this altitude. They're the first clouds to catch the colour at sunrise and sunset, and often the first visible sign of a warm front still a day or more away.

Cirrus clouds - thin white wispy streaks high in the sky
Cirrus (Ci)

Latin: cirrus, "a curl of hair"

Delicate, detached white filaments or narrow bands, often with a silky or fibrous sheen. Made entirely of ice crystals, which is why they rarely dim the sun even when fairly extensive.

What it usually means: Scattered wisps on their own are no great signal, but cirrus steadily thickening and lowering over several hours often marks the leading edge of an approaching warm front, a day or so ahead of rain.
Cirrocumulus clouds - small white patchy ripples high in the sky
Cirrocumulus (Cc)

Latin: cirrus + cumulus

A thin, white, patchy sheet of small ripples or grains with no shading, each element narrower than a little finger held at arm's length. Short-lived, and usually forms from cirrus or cirrostratus breaking up.

What it usually means: The classic "mackerel sky" — an old sailors' rhyme ("mackerel sky, not long wet, not long dry") reflects that it often signals unsettled weather is on the way, though rarely with much notice.
Cirrostratus clouds - a thin whitish veil covering the whole sky
Cirrostratus (Cs)

Latin: cirrus + stratus

A transparent, whitish veil, fibrous or smooth, that can cover the entire sky without ever fully blotting out the sun. The giveaway sign is a halo around the sun or moon, caused by light refracting through the ice crystals.

What it usually means: One of the most reliable "rain within 24 hours" signs in traditional weather lore — it's the layer directly ahead of an advancing warm front.

Mid-Level Clouds — roughly 2,000-6,500m (6,500-20,000ft)

Made mostly of water droplets, sometimes ice at the colder end of the range. Confusingly named with the Latin prefix "alto" (meaning high) even though they sit in the middle band — the name exists simply to distinguish them from their low-level look-alikes, stratus and cumulus.

Altocumulus clouds - white and grey patchy rounded masses in the middle sky
Altocumulus (Ac)

Latin: altus + cumulus

White or grey patches, sheets or rolls, each element between one and five finger-widths at arm's length — noticeably bigger than cirrocumulus. The most common mid-level cloud, often appearing in several layers at once.

What it usually means: On a humid summer morning, altocumulus that builds noticeably by mid-morning is a classic warning sign of thunderstorms developing later in the day.
Altostratus clouds - a grey or bluish featureless sheet across the sky
Altostratus (As)

Latin: altus + stratus

A grey or bluish sheet, thin enough that the sun still shows through as if seen through ground glass, but without the halo effect that marks out cirrostratus.

What it usually means: Usually the next stage after cirrostratus as a warm front gets closer — expect the sky to keep thickening and rain to follow within several hours.
Nimbostratus clouds - a thick dark grey rain-bearing layer
Nimbostratus (Ns)

Latin: nimbus + stratus, "rain cloud"

A thick, dark grey layer that fully blots out the sun, usually already producing steady rain or snow by the time it's overhead. Its base often lowers further as precipitation continues, which is why it's easy to mistake for a low cloud even though it starts in the mid-level band.

What it usually means: This is the rain cloud itself, not a warning sign of one — if nimbostratus is overhead, the steady rain has already arrived.

Low-Level Clouds — surface up to roughly 2,000m (6,500ft)

Made of water droplets, and the clouds people notice most because they're closest to the ground. One member of this group, cumulonimbus, is the exception that breaks every rule — its base sits low but its top can punch straight through the mid and high levels into the stratosphere.

Cumulus clouds - detached white fair-weather clouds with flat bases and rounded tops
Cumulus (Cu)

Latin: cumulus, "a heap"

Detached, sharp-edged heaps with flat, dark bases and brilliant white, cauliflower-like tops. The classic "fair weather cloud", forming through the morning as the ground heats up and mostly dissolving again by evening.

What it usually means: Small, well-separated cumulus with flat bases is one of the best signs of a settled, dry day. Watch for it growing taller and more crowded through the afternoon — that's the first stage toward a shower.
Cumulonimbus clouds - a towering storm cloud with a flattened anvil top
Cumulonimbus (Cb)

Latin: cumulus + nimbus

The thunderstorm cloud: a huge, dense tower with a smooth or fibrous top, very often flattened into the classic anvil shape where it hits the tropopause and can rise no further. Produces heavy rain, hail, lightning and, occasionally, tornadoes.

What it usually means: Active weather right now or within the hour — treat an anvil-topped cumulonimbus as a lightning risk even if it looks some distance away.
Stratocumulus clouds - grey patchy rounded masses low in the sky
Stratocumulus (Sc)

Latin: stratus + cumulus

Grey or whitish patches, sheets or rolls with a honeycomb-like or tessellated appearance, each element wider than three finger-widths at arm's length — noticeably bigger than altocumulus.

What it usually means: The most common cloud type over the UK by a wide margin. Rarely produces more than occasional light drizzle, but a persistent grey stratocumulus sheet is why so many British days feel duller than they actually are, rainfall-wise.
Stratus clouds - a uniform grey featureless layer close to the ground
Stratus (St)

Latin: stratus, "a layer"

A uniform, featureless grey layer with a flat base, often sitting almost at ground level. When the sun shows through, its outline is clearly visible, unlike the diffuse glow through nimbostratus.

What it usually means: At its lowest, this is simply fog that hasn't quite reached the ground — very common in the Solent area on still, clear mornings before the sun burns it off.

Quick Reference Table

CloudCodeHeight BandMade OfTypical Signal
CirrusCiHighIceFair weather now, front possibly a day out
CirrocumulusCcHighIce"Mackerel sky" — change coming
CirrostratusCsHighIceRain within 24 hours (haloed sun/moon)
AltocumulusAcMidWater/icePossible storms later if building fast
AltostratusAsMidWater/iceRain within several hours
NimbostratusNsMid (base can lower)Water/iceSteady rain in progress
CumulusCuLowWaterFair weather; watch for growth
CumulonimbusCbLow base, top to highWater/iceThunderstorm, active now
StratocumulusScLowWaterDull skies, little rain
StratusStLowWaterFog/mist, may just be low cloud

Cloud Spotting Around Southampton

The Solent's coastal position makes stratus and shallow stratocumulus especially common here — overnight radiation fog frequently lifts into a low stratus deck rather than clearing completely, particularly in autumn and winter when the sea is still relatively mild compared with cooling land air. Towering cumulus and the odd cumulonimbus are more of a spring and summer feature, often arriving on a south-westerly airflow after a spell of humid, unstable weather. For the live picture right now, our satellite imagery pages show the cloud actually overhead.

↑ back to top