• Question: Why do pink skies at night mean that it won't rain the next day?

    Asked by Zealousy to Chris, Josh, Rebecca, Rob, Susan on 22 Jun 2015.
    • Photo: Rebecca Dewey

      Rebecca Dewey answered on 22 Jun 2015:

      The atmosphere is made up of molecules (water and air mostly), and these molecules scatter any light that travels through them – i.e. they send the light going in all different directions. Also, each time the light travels through a water droplet, its wavelength changes because it is travelling through the water.

      But in the evening (dusk) or first thing in the morning (dawn), the light has to travel through a thicker amount of atmosphere because it is coming to us from a lower angle in the sky, rather than from right over head. Because of this, a lot more scattering takes place and the sky colour changes by a greater amount. If there is cloud on the horizon, this scattering becomes even greater, so the sky turns pink.

      So if these clouds are on the horizon, then they are probably either moving away from us or moving towards us. So either it means that it won’t rain the next day, or it means that it is more likely to! Basically, it’s not a very reliable way of telling whether or not it is going to rain the next day!

    • Photo: Susan Cartwright

      Susan Cartwright answered on 22 Jun 2015:

      As I am not a meteorologist, I am just going to quote from the Met Office webpage:

      “The saying is most reliable when weather systems predominantly come from the west as they do in the UK. “Red sky at night, shepherds delight” can often be proven true, since red sky at night means fair weather is generally headed towards you.

      A red sky appears when dust and small particles are trapped in the atmosphere by high pressure. This scatters blue light, leaving only red light to give the sky its notable appearance.

      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.”

      (http://www.metoffice.gov.uk/learning/learn-about-the-weather/how-weather-works/red-sky-at-night)

Comments