Sailors have long observed the sky for signs of changing weather. One well-known old sailor’s rhyme goes: “Red sky at night, sailor’s delight. Red sky in morning, sailors take warning.” This rhyme summarizes the idea that red skies in the morning often indicate that poor weather is coming, while red skies in the evening suggest that fair weather is on the way.
What causes red skies?
Red skies are caused by the scattering of sunlight through dust particles and water droplets in the atmosphere. Different factors can contribute to red skies at different times of day:
- In the evening, sunlight scattering through dust and moisture particles in the west often produces vivid red colors as the sun sets.
- In the morning, red skies are often caused by dust particles and moisture in the east ahead of an approaching weather disturbance like a storm system.
The sinking motion of air in high pressure areas causes dust and moisture to accumulate, while rising air in low pressure disturbs the atmosphere. That’s why red skies at night around high pressure often mean fair weather is coming, while morning red skies with approaching storms tend to mean unsettled weather.
The science behind “red sky at night”
Let’s look closer at the science behind the “red sky at night” part of the saying first. Here’s a quick overview of why red evening skies often mean fair weather is coming:
- High pressure systems have sinking air that allows dust, moisture, and pollution particles to accumulate overhead.
- The sinking air is warmer and drier, meaning fair weather.
- Sunlight scattering through those particles creates vivid red hues as it passes through the atmosphere in the west at sunset.
- The clear, stable air means good visibility for enjoying those sunset colors.
- Therefore, red skies at dusk imply fair weather ahead under the high pressure region.
In essence, the dry, stagnant air in high pressure areas provides ideal conditions for vivid sunsets. Let’s look at an example to see how this works:
| Time | Weather Conditions | Explanation |
|---|---|---|
| Day 1 | A high pressure system is centered west of your location. Sinking air causes warm, dry conditions. Dust and moisture accumulate overhead. | The sinking air traps dust and moisture. Stable conditions set the stage for red sunset skies. |
| Evening | Skies turn vivid red and orange during sunset. Excellent visibility provides great sunset viewing. | Sunlight scatters through the dust and moisture particles overhead, creating a vivid red sky. |
| Day 2 | The high pressure system moves overhead, bringing sunny, fair weather. | The red sky at dusk was a sign of the fair weather conditions to come under the high pressure. |
In this example, the red sunset sky on Day 1 was a visual clue that fair weather was on the way as the high pressure system approached on Day 2, just as the saying suggests.
The science behind “sailors take warning”
Now let’s examine why red morning skies are often a warning sign for sailors:
- Low pressure systems have rising air that disturbs dust and moisture.
- The rising air forms clouds and precipitation associated with storms.
- Sunlight scattering through those disturbed particles creates a reddish sky in the east ahead of the storm.
- Therefore, red mornings are a warning that unsettled weather is approaching from the west.
Rising unstable air ahead of a storm system stirs up the atmosphere, causing the red morning light sailors would want to heed as a warning. Here’s an example scenario:
| Time | Weather Conditions | Explanation |
|---|---|---|
| Day 1 | A low pressure system is approaching from the west, with unstable air. Moisture and dust are lifted upwards. | The rising air disturbs particles high in the atmosphere ahead of the storm. |
| Morning | Skies turn red in the east around sunrise. Clouds increase through the day. | Sunlight scatters through the disturbed air, creating a red eastern sky. |
| Day 2 | The low pressure system brings rain and wind. Unsettled weather lingers. | The morning red sky was a warning sign of the approaching storm’s poor weather. |
Here the red colors visible in the east before the storm arrived served as a tell-tale warning for sailors that disturbed weather was on the horizon.
How accurate is the saying?
The general principles behind the red sky saying are scientifically sound. However, like any weather lore, there are exceptions. Here are some caveats:
- Red skies happen for reasons besides winds associated with pressure systems, like dust storms or forest fire smoke.
- Red morning skies don’t always mean storms later that day. It may take 18-24 hours for an approaching system to arrive.
- Similarly, red evening twilights don’t guarantee the next day will be sunny and fair, just that high pressure is nearby.
- The rhyme is most applicable to mid-latitude regions. In the tropics, localized weather dominates over large-scale pressure systems.
The saying is not 100% foolproof, but it summarizes a general rule. A red sky at night linked to high pressure often does indicate fair weather to come for at least a day or so. Meanwhile, vivid red mornings suggest unstable conditions that typically precede a low pressure storm system by a day or more.
Conclusion
The old sailor’s saying about red skies contains wisdom gained from generations of observation. While not perfect, it captures the typical warning signs of rough weather approaching and hints of fair weather returning. This rhyme remains popular because it neatly summarizes the different red sky conditions caused by rising and sinking air masses. So while red skies alone may not say everything about what’s ahead, they remain a useful visual clue for reading changing weather patterns.
