A Field Guide to Cloud Types: How Cumulus, Stratus, and Cirrus Predict the Weather

Before radar, before satellites, before NWP models — before any of modern meteorology existed — people predicted weather by watching clouds. Not vaguely. Specifically. The system of cloud classification that Luke Howard proposed in 1803 is still the foundation of how meteorologists categorise clouds today. Because clouds really do tell a coherent story about what the atmosphere is doing, if you know how to read them.

The Low Clouds — Below 2,000 Metres

Cumulus clouds are the photogenic ones — white, puffy, distinct boundaries, flat base, cauliflower top. In the morning, fair-weather cumulus developing after sunrise are a good sign; the atmosphere is stable, convection is developing but not intensifying. If they're small and stay small through the day, you probably have a fine afternoon.

Watch them carefully from noon onwards. If they start growing vertically — building upward instead of just drifting horizontally — that's a developing convective tower. If the top starts looking hard and cauliflower-like and the base darkens: cumulonimbus development. You have roughly 30–60 minutes before that becomes a thunderstorm. This is exactly what lifeguards and cricket umpires are watching when they "check the horizon."

Stratus clouds are grey, flat, featureless sheets that cover the entire sky. They don't produce heavy rain — usually light drizzle if anything — but they can persist for days and are associated with the kind of damp, gloomy weather that settles over coastal cities during the monsoon's overcast phases. They form when stable air is forced to rise gently over a warm or cold front, or when fog lifts slightly off the ground.

The Middle Clouds — 2,000 to 6,000 Metres

Altocumulus is the cloud that appears in small, rounded patches or rows — sometimes described as a "mackerel sky" because the pattern resembles fish scales. It often precedes a weather system by 12–24 hours and is worth noting if you see it on an otherwise clear day. Altostratus is a thicker, grey-blue sheet at mid-level that usually means rain is coming within 12–24 hours — it's often the layer you see just before a proper monsoon depression moves in, as the sky progressively thickens from cirrus to altostratus to nimbostratus.

The High Clouds — Above 6,000 Metres

Cirrus clouds are the thin, wispy, hair-like strands made entirely of ice crystals (it's cold up there — typically -40°C to -60°C). They appear during fair weather but are often advance messengers of approaching warm fronts. A sky that was clear and blue fills gradually with cirrus, then thickens to cirrostratus, then altostratus — this progressive cloud sequence is a classic 24–48 hour signal of incoming rain from an approaching weather system.

If you see a bright halo around the sun or moon, that's light refracting through cirrostratus ice crystals. The old saying "ring around the moon, rain coming soon" is actually a reasonable indicator — it means cirrostratus is present, and if a warm front is responsible, rain probably is coming in the next 24–36 hours.

You don't need an app to read the basics. A few minutes of genuine sky observation, with a sense of what each cloud type means, gives you a useful second opinion alongside any digital forecast.