Why is the sky red? What the colour of the sky says about the weather to come

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Learn to predict the day’s weather judging from the colour of the sky.

Sunsets and sunrises are known to be more impressive during the colder winter months.

What’s more, we’re more likely to be out and about to see them, what with the clocks going back and the shorter days.

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Wintry dawn and dusk skies are often a riot of colour, with fluffy clouds tinged with shades of pink and red.

Next time you spot a red sky in the morning, you'll know what weather to expect for the day. Photo: George Becker / Pexels / Canva Pro.Next time you spot a red sky in the morning, you'll know what weather to expect for the day. Photo: George Becker / Pexels / Canva Pro.
Next time you spot a red sky in the morning, you'll know what weather to expect for the day. Photo: George Becker / Pexels / Canva Pro.

However, colourful skies in the morning and at night aren’t just a pretty sight.

You might well have grown up hearing the saying:

‘Red sky at night, shepherd’s delight. Red sky in the morning, shepherd’s warning’.

So how true is the old rhyme? Here’s all you need to know about red skies and their ability to predict the weather.

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Why is the sky red in the morning?

Periods of high pressure in the winter produce the cold, crisp, dry days that we’re well used to in Scotland and across the UK.

Light winds are also common, which means dust and other particles can get trapped in the atmosphere.

As the sunlight shines through on one of these crisp days, red wavelengths pass through the air more easily than blue ones.

The blues are scattered and deflected, while the reds reach our eyes down on the ground.

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As a result, these red wavelengths colour the sky more deeply than the blue ones.

The more white clouds there are, the better, as the light is reflected back to be made more intense and the clouds themselves are coloured pink.

What does a red sky say about the weather?

In the UK, weather systems tend to move predominantly from west to east.

In terms of the weather, that means that having a red sky in the morning is a sign that the sky is clear to the east, where the sun is rising, as the red wavelengths are passing through easily.

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However, it also suggests that it’s cloudy overhead, with the sunlight bouncing off the clouds.

This would suggest that bad weather like rain or fog is to come, with heavy clouds nearby.

However, in other parts of the world with more tropical weather, the winds blow in the opposite direction, making this rule less likely to be correct.

Naturally, it’s not always a hard and fast rule. The UK is known for having unpredictable weather and winds can blow the clouds in different directions at times.

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Nonetheless, it can offer a good indication of how to plan your day judging from the colour of the sky when you first wake up.

Where does the saying about red skies come from?

Going back to the old saying about the shepherds, the shepherd’s delight refers to good weather, while shepherd’s warning refers to bad weather.

Some variations of the rhyme also refer to sailors, another profession that relies on being outside and having good weather.

The saying was first said by Jesus in the Bible, meaning it’s well over 2,000 years old at this point.

Back then, sailors and shepherds alike didn't have a Met Office weather forecast to rely on, so it’s no wonder they looked for any possible sign from nature for what they could expect.

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