Sitting at my desk and watching the sunset It made me think of “red sky at night shepherds delight” which prompted the questions “Why do we say it? and “Is it true, can it predict the coming weather?”.
The First question “why?” is fairly straightforward to answer because throughout history memorable rhymes and sayings have been used to predict the weather based on human repeated experience. These sayings are more prevalent within occupations or communities that rely on knowing the weather to bring in the harvest or shelter from a storm at sea.
So Let us begin with question two “Is it true?”…
The History
“Red sky at night, shepherd’s delight. Red sky in the morning, shepherd’s warning” Is probably one of the most famous weather related sayings, and one most people would be familiar with, probably due to the very obvious identification of a red sky. The saying first appears in the Bible in the book of Matthew. (16 v2-3,) Jesus (apparently) said, “When in evening, ye say, it will be fair weather: For the sky is red. And in the morning, it will be foul weather today; for the sky is red and lowering”. Throughout the generations it has stuck and transformed into the various versions we know today.
In order to understand why the developed saying of “Red sky at night, (enter a profession here) delight. Red sky in morning, (enter a profession here) warning” can predict the weather, we must understand more about weather and the colors in the sky.
NB: Usually, weather moves from west to east. In the mid-latitudes, the prevailing winds are westerlies. This means storm systems generally move in from the West.
The Colour
The colors we see in the sky are due to the rays of sunlight being split into colors of the spectrum as they pass through the atmosphere and ricochet off the water vapor and particles in the atmosphere.
The amounts of water vapor and dust particles in the atmosphere are good indicators of weather conditions.
During sunrise and sunset the sun is low in the sky, and it transmits light through the thickest part of the atmosphere. A red sky suggests an atmosphere loaded with dust and moisture particles. We see the red, because red wavelengths (the longest in the color spectrum) are breaking through the atmosphere. The shorter wavelengths, such as blue, are scattered and broken up.
The Science
It would seem that the saying is most reliable when weather systems predominantly come from the west as they do in the UK and most of Europe. “Red sky at night” can often be proven true, since red sky at night means fair weather is generally headed towards you.
A red sky at sunset means high pressure is moving in from the west, so therefore the next day will usually be dry and pleasant.
“Red sky in the morning, shepherds warning” means a red sky appears due to the high-pressure weather system having already moved east meaning the good weather has passed, most likely making way for a wet and windy low-pressure system.
What is it going to be tonight?