Guide · Weather and nature

Reading the clouds

Without a forecast, the sky is your best guide to what the weather will do next. Clouds can warn you of rain, wind or storms hours before they arrive, giving you time to find shelter or change plans.

Fair weather clouds

• Small, puffy cumulus with flat bases and clear blue gaps usually mean settled weather. If they stay small through the day, conditions are likely to stay fine.
• Clear skies at night let heat escape. Expect a cold night, and possibly frost, dew or fog by morning.

Signs of rain on the way

A common sequence warns of an approaching band of rain, often over 12 to 24 hours:

1. Thin, wispy cirrus high in the sky, sometimes called mares' tails.
2. They thicken into a milky veil called cirrostratus. A ring, or halo, around the sun or moon often appears at this stage.
3. The cloud lowers and thickens into grey altostratus. The sun looks as if it's behind frosted glass, then disappears.
4. Low, dark nimbostratus brings steady rain or snow.

If you see this pattern developing, plan to be somewhere sheltered within the day.

Signs of thunderstorms

• Cumulus clouds that grow tall through the day, with hard, cauliflower-like tops, are building energy.
• When they tower very high and spread into a flat anvil shape at the top, they have become cumulonimbus — thunderstorm clouds.
• Expect heavy rain, hail, gusty winds and lightning. Storms can form within an hour or two on hot, humid afternoons.
• A dark, low, rolling band of cloud at the front of a storm often brings a sudden, strong gust.

Signs of strong wind

• Lens-shaped clouds sitting still over hills or mountains, called lenticular clouds, show strong winds high up. Conditions on high ground may be dangerous.
• High clouds racing across the sky suggest wind is on the way, even if it's calm where you are.

Low cloud and fog

• Flat grey stratus may bring drizzle and poor visibility, especially on hills.
• Cloud sinking onto summits means visibility on high ground is about to drop. Take a compass bearing while you can still see.

Other clues

• A sudden drop in temperature, or the wind changing direction, often comes just before a change in weather.
• Morning mist that clears by mid-morning usually means a fine day.
• If your watch or phone has a barometer, steadily falling pressure suggests worsening weather.

Trust what you see

If the sky looks threatening, act early. It's always easier to find shelter, turn back or come down from high ground before the weather arrives.

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