Red sky at night, sailors delight: does it work?

What does red sky at night, sailors delight mean?

The full rhyme says a red sky at night is a sailor's delight, and a red sky in the morning is a sailor's warning. The saying is old. Wikipedia notes that it is cited in the New Testament at Matthew 16:2 to 3 as established wisdom of the first century, so the idea is over two thousand years old (Wikipedia: Red sky at morning).

Versions swap sailors for shepherds, and some use pink in place of red.

Why would a red sunset mean good weather?

In mid-latitudes, weather usually travels from west to east. At sunset you look west, toward what is coming. A red sky there suggests dry, stable air carrying dust and other particles, which scatter the blue light and leave the reds. High pressure means settled weather, so a red western sky points to a high on its way.

At sunrise you look east, toward what has just passed. A red morning sky can mean the clear air has gone by and a low-pressure system is arriving from the west.

Where does the rhyme go wrong?

Wikipedia notes that because prevailing winds differ around the globe, the rhyme is generally not correct at lower latitudes in either hemisphere, where winds blow from east to west. It is generally correct at middle latitudes, where winds travel west to east.

A storm can also rain itself out before it reaches you. For ships at sea, strong wind and rough water can still arrive without rainfall.

Is there evidence it is right?

The stable-air logic is sound for the regions where the rhyme applies, and it is the reason the saying has lasted. Treat it as a hint, not a measurement. One red evening does not guarantee a dry night. Combine it with a pressure trend, a wind direction check and a real forecast.

How is a red sunset different from a good forecast score?

The rhyme reads the color of the sky that you already see. A forecast looks at the atmosphere before the color forms. A score such as the Glow Score estimates how likely the sky is to light up, using high and mid clouds, low clouds toward the sun, air and rain. It does not predict tomorrow's weather. It answers a narrower question: is this evening worth stepping out for?

What does a colorful sunset say about the air?

Scattering depends on particles. Dust, smoke and humidity change how much blue gets removed and how bright clouds light up. Our guide to why sunsets are red walks through the physics, and the piece on what makes a good sunset covers which weather gives the best color.

Can I try the rhyme myself?

Yes, and it makes a nice project. Write down what the sky looked like at sunset and whether the next day was fair. After a few weeks you will have your own record for your own climate.

1. Note the date, place and sunset color.
2. Write the wind direction and whether the pressure was rising or falling, if you have a barometer app.
3. Record the next morning's weather.
4. After 20 entries, count how often the rhyme matched.

What about a red sky in the morning?

The other half of the rhyme is the warning. At sunrise the sun lights clouds from the east, and in mid-latitudes the weather is coming from the west, hidden behind you. A red sky at dawn often means the sunlight is catching high cloud that is the front edge of an approaching system. Sailors took that as a prompt to check their lines before the wind rose.

It is a weaker signal than the evening version, since a red dawn also happens on plenty of dry days.

How do dust and smoke change the story?

Particles in the air add color and break the logic of the rhyme. Smoke from wildfires or dust blown from a desert can turn a sunset deep red on a day when the weather has nothing to do with the sky. In that case the color tells you about the air, not about tomorrow's pressure. Our article on wildfire smoke and sunsets covers how that works.

How should I use the rhyme today?

Use it as a nudge to look at the real forecast, not as a replacement. If the sky is red tonight and the forecast agrees, plan for a fair day. If the sky is red and the forecast shows rain, believe the forecast. Folk wisdom is a good place to start a question, and a weather model is a better place to end it.

How can I keep a record of sunsets?

Afterhue lets you rate each evening with four buttons, Flat, Soft, Glowing and On fire, and saves a Hue Chip with the date, place and colors if you photograph it. That gives you a sky diary you can compare with the weather that followed, and the Sky Strip shows your year at a glance.