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Weather Why: Red Sky at Night, Sailors’ Delight…

We’ve all heard it.

Red sky at night, sailors’ delight. Red sky in the morning, sailors take warning.

But what if I were to tell you that this old saying actually has a bit of truth to it!

The Lore

The lore itself dates all the way back as far as the bible!

Jesus himself 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.”

Don’t believe me? Go look it up– Matthew Chapter 9, verses 2 – 3!

It wasn’t just the Bible, Shakespeare himself passed on the old proverb.

But is there any truth to it?

The Science

Believe it or not, atmospheric science actually supports this old bit of wisdom.

High and Low Pressure

In a very broad sense, if your trace a latitude around the globe you will find ridges and troughs. Or more colloquially, High and Low pressure centers.

  • Low Pressure
    Associated with stormy weather, a low pressure center is an area of rising air in the atmosphere. The rising motion relieves the pressure down on the surface (thus lower pressure) but also causes the formation of clouds and storms.
  • High Pressure
    Associated with dry weather and sun, a high pressure is an area of sinking air in the atmosphere. The sinking or subsidence in the atmosphere is what keeps the skies clear (for simplicity) but also causes a higher concentration of atmospheric particulates or aerosols down near the surface.

Aerosols

Aerosols are the tiny particles in the atmosphere that you can’t typically see with your naked eye. And they actually play a huge role in our weather and climate as well.
Don’t believe me?

This old proverb was about aerosol concentration long before we knew anything about it!

In an area of high pressure the subsidence means more aerosols down near Earth’s surface. These aerosols actually scatter the incoming sunlight, keeping different wavelengths of light from reaching us as observers.

Sunlight or white light comes in as a full color spectrum of the rainbow. Shorter wavelengths are on the blue end of the color spectrum while longer wavelengths are on the red end of the spectrum.
The concentration of aerosols keeps the shorter wavelengths of light from reaching our eyes. While the longer wavelengths like the reds push through, acting almost like an aggressive Instagram filter in real life!

Put It All Together

Since we are only focusing on the red sunrises and sunsets, we only need to talk about high pressure when it comes to this particular bit of lore.

Assuming predominately westerly flow (between 30 and 60 degrees latitude) it all works out quite nice.

Red Sky at Night

A red sunset means there is a ridge of high pressure to the west. (Sun sets to the west)
And since weather patterns move west to east, the red sunset means high pressure is moving in.
Thus clear skies and a sailors delight!

Red Sky in the Morning

A red sunrise means there is a ridge of high pressure to the east. (Sun rises in the east)
And since weather patterns move west to east, the red sunrise means high pressure is moving out.
Thus, a low pressure center must be moving in, and along with it storms!

Take Note

This doesn’t just happen out at sea!
You too can observe this neat little bit of weather lore in your own backyard!

So get out the camera and let us know what kind of weather you are seeing associated with these red sunrises and sunsets!

 

For WeatherNation, Meteorologist Jeremy LaGoo

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