Weather Blog

Red sky at night, but should sailors really care?

Red sky at night, but should sailors really care?
Dianne Horne, Blaine, WA
We had quite a few e-mails from people wondering about the brilliant red sunset Tuesday night.  Some even wondered if it was smoke from nearby wildfires that was responsible.

I'm not 100% sure, but my best guess is that it is a combination of our smoggy air and smoke from the Northern California wildfires. We do have a south wind aloft and that is likely tapping into the smoke and pulling it up our way.

But why a red sky? You normally see sunlight as white, but it's actually made up as a combination of the colors of the spectrum.

Smog, dust or dirt particles will scatter away some of those colors -- the blues, greens and violet colors have shorter wavelengths and thus more likely to hit a particle and be deflected. The reds and oranges have longer wavelengths and thus are more robust and will do a better chance of making it through the atmosphere unscathed. This is also similar physics to why the sunsets are usually brilliant colors -- the sun has to shine through a thicker part of the atmosphere when it is low on the horizon so more of the greens and blues are lost, and the sky turns red, pink and orange.

And when you've got additional factors such as that smog, dust, or even ash or smoke, the reds are enhanced as there's even more particles to scatter away the shorter-wavelength part of the spectrum.

Now, as for the title of this blog entry, you've probably heard the saying "Red sky at night, sailor's delight. Red sky at morning, sailor's take warning."

That lore is based on a clear sky at evening twilight (as in, being able to see the colors of the sunset). If you can see the sunset, that means it's clear to the west. Since weather generally moves west to east, that would mean there are no storms in your immediate future and sailors, along with sun fans and those who forgot to put their top up on your convertible, would be delighted.

The red sky at morning is a bit more dubious. That is assuming that if the weather is clear to your east (as in, you can see the sunrise) then based on natural progression of weather, it must mean a storm is due to come in from the west, and sailors should take warning.

It's reasonable advice if you are sailing in the mid-latitudes, but if you're a sailor in the tropics or, say, off the coast of Southern California, it's likely clear to the east *and* the west.

Or better yet, just enjoy the sunrise -- and get yourself a good weather radio :)