Red sky at night, shepherd's delight?

Imagine a world where immediate access to reliable weather forecasts did not exist. How many layers would you wear today? Would you pack an umbrella? It's likely you'd get caught out by the weather a little more, but after living in a pre-weather-forecast-world for a little while, you may start to develop your own predictions for the weather. It was from human experience that old forecasting phrases were born, and we still know these sayings today because some of them often worked and helped our ancestors plan for the upcoming weather. So is there any meteorological foundation to the saying "red sky at night, shepherd's delight; red sky in the morning, shepherd's warning"?

The sky appears a glorious pink/red when aerosols (small particles) in the atmosphere preferentially scatter the blue part of the Sun's light spectrum, meaning our eyes receive a more reddish colour from the sky. The preferential scattering requires a low incident angle from the Sun, hence why this phenomena occurs at sunrise or sunset. Also required are the small atmospheric particles, which often exist in greater concentrations when high pressure dominates.

If there is red sky whilst the sun sets in the west, there is likely to be high pressure to the west of our location. If the high pressure is moving east it will soon reach our location, often bringing pleasant, stable conditions with it - a shepherd's delight. Because weather systems predominantly come from the west in the UK, red sky at night is often followed by high pressure and calm weather.

Red sky at night over the University of Leeds on 30/11/16.

However, red sky as the sun rises in the east tells us at there is likely to be high pressure to the east of our location. Under the predominantly easterly-moving weather systems over the UK, the high pressure departs further east of our location and as it moves out, low pressure often takes it place. Low pressure systems are associated with more wet, windy weather, so the morning red sky comes as a warning - poor weather conditions are coming!

Red sky in the morning over Leeds on 05/12/16

Unfortunately, the complex nature of the atmosphere makes this old saying not so straight forward. Weather systems reach the UK from every direction, not just from the west. Small particles do not only exist in the atmosphere under high pressure, either, so it is possible to have a red sky when low pressure is present in the direction of the Sun.

Nevertheless, this saying, like other old weather proverbs and stories, give us an idea of what weather forecasting consisted of before today's meteorological understanding and accuracy.