What is a Fire Rainbow? How Rare is It to See Fire Rainbows?

Have you ever been driving your RV or hiking a trail and notice a cool looking rainbow resembling a flame? You’ve just witnessed a rare phenomenon referred to as a Fire RainbowBut, did you know a fire rainbow is actually not a rainbow as you may be familiar with? And a fire rainbow has nothing to do with fire?

Cover Photo Source: Almanac.com

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I’m always looking at the sky. I admit, I’m a tripping hazard. It’s not because I’m clumsy. And, it’s not because I’m in Lala Land or carelessly walking with my nose to the phone.

It’s because I’m always looking up at the sky. Dan often notices that I gaze at the sky more than where I should be stepping or walking.

Ever having been a ship’s navigator, I learned everything from actually steering and maneuvering a ship or boat. But I also studied weather and how to read the sky. You know, the clouds?

Recollecting back to my navigation school, most of the time I can read the sky and tell what the weather is going to be…and be correct!

If I see something weird going on up there that I’m unfamiliar with (like weird looking clouds), I will look it up so I can make big bucks on Jeopardy someday.

And so this brings me to a strange heavenly phenomenon we witnessed while we were road tripping up in Minnesota.

Looking through the windshield, I noticed a strange looking rainbow that wasn’t the typical arc form that we’re all used to seeing after rain. You know, the one on the Lucky Charms cereal box?

So, when we got back to our campsite, I dove right in to learn about this so called flame-shaped rainbow in the sky also known as a Fire Rainbow.

What I learned about fire rainbows is actually intriguing; thus, why I’m sharing it here.

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What is a Fire Rainbow?

How Rare is It to See Fire Rainbows?

Fire Rainbow - Tiffany Jenks REX - Always On Liberty
Fire Rainbow – Image Source: Mirror  –  Image by: Tiffany Jenks/REX)

What is a Fire Rainbow?

A fire rainbow, also called a circumhorizontal arch, is an optical phenomenon from ice halos.

Fire rainbows always occur at a fixed location in relation to the Sun or Moon, whereas cloud iridescence can occur in different positions in the sky.

Even more interesting, the varigated color bands always run horizontally with red at the top and violet at the bottom per the VIBGYOR color spectrum.


Why are they called fire rainbows?

While fire rainbows, or rainbow fire clouds, have nothing to do with fire, they are called fire rainbows because of their flamelike appearance with brilliantly colorful radiance.

What causes a Fire Rainbow?

Fire Rainbow - Formation of circumhorizontal arcs - Always On Liberty
Formation of Circumhorizontal Arcs or Fire Rainbows – Image via North Coast Journal.

Fire rainbows form in high altitude Cirrostratus or Cirrus clouds by refracting sunlight through plate-shaped ice crystals that suspend in the atmosphere. The clouds are what makes the colors appear soft and wispy.

Cirrostratus or Cirrus clouds are fair weather clouds that look like wispy mare’s tails or soft willowy feathers in the sky. These high altitude clouds are the first inclination of an upper level jet stream or approaching warm front.

Cirrus clouds are typically more concentrated. Whereas Cirrostratus clouds are more widespread across the sky; oftentimes looking like white wedding veil.

At least that’s a simple way it was put to us in our weather class in my nautical navigation school.

What’s this Cloud explains,

“Cirrus and Cirrostratus clouds are found at the same altitude and both can be fibrous in nature. When deciding between the two, remember that a cirrostratus cloud generally covers the sky and is more of a pale, veil-like layer cloud, where you’ll generally see more individual elements in a cirrus cloud, such as comma shapes, fishbone-like shapes, and other wispy shapes.”

Even more interesting, a fire rainbow phenomenon can also occur at night. The same way the light refracts from the sun can equally happen as the moon’s light refracts through those high altitude ice crystals.

What is light refraction?

Light Refraction Diagram - Wikipedia
Light refracting through a water drop. Source: Wikipedia

What is light refracting, you ask? In layman’s terms and according to the National Weather Service and National Oceanic Atmospheric Administration (NOAA), refraction is the change in direction of a wave, such as sunlight or moonlight, due to a change in its speed.

This most commonly occurs when a wave passes from one medium to another at any angle other than 90° or 0°.

So, when light is refracted inside an ice crystal or water droplet in the air, its broken into its color spectrum. This creates the rainbow effect.

What is the difference between fire rainbow and rainbow?

The phenomenon of a fire rainbow differs from the common rainbow. Though a fire rainbow may look like an actual rainbow, fire rainbows are not rainbows. Oddly, hence their name, fire rainbows have nothing to do with fire.

Unlike the common rainbow, fire rainbows are, instead, a halo formed by light refracting from the sun through the clouds.

As best compared, fire rainbows refract light through ice crystals. Whereas, a typical arched rainbow refracts light through water droplets.

Fire Rainbow - Dehk at Wikipedia
Fire Rainbow – Image Source: Dehk at Wikipedia

How rare are fire rainbows?

To observe a fire rainbow is actually quite rare because certain atmospheric conditions must align systematically for the fire rainbow phenomenon to occur.

One important note though. Fire rainbows aren’t seen just anywhere from the globe. Unfortunately, if you’re position is north of 55N or south of 55S, your chances of getting to see a fire rainbow are almost nonexistent.


Is a fire rainbow the same as a sun dog?

Sundogs Over Winter Landscape - Always On Liberty
Sundogs over winter landscape – Photo source: Canva

A rainbow forms after or during rain when sunlight bends when it moves through minuscule water droplets. A fire rainbow forms in high altitude when the sun (or moon) lights refracts through ice crystals but displays the color spectrum horizontally in the sky.

In contrast to a fire rainbow or the common rainbow, a sundog typically forms on days of high altitude clouds with no precipitation.

A sundog, also known as a perihelia or mock sun, means with the sun. Sundogs are colored spots of light or vertical rainbows that occur when sunlight scatters and refracts through plate-like, hexagonal-shaped ice crystals in high altitude cirrus or cirrostratus clouds.

The vertical rainbow colors typically start with red closest to the sun, out to blue on the outside of the sundog. 

According to Space.com, sun dogs occur at high altitudes above 20,000 feet or 6,000 meters and higher, up to 40,000 feet or 12,000 meters.

Much like prisms, the crystals that refract light align vertically which creates a rainbow streak affect. On really cold days, they may appear like diamond dust that literally glistens in the sky.

Where can you see Sundogs?

Sundogs are located approximately 22 degrees either left, right, or both, from the sun, depending on where the ice crystals are present,” says Weather.com.

What are the conditions for a fire rainbow to occur?

For a fire rainbow to occur, the conditions for them to form must be extremely precise. Recapping, three things must align perfectly. And this is precisely why circumhorizontal arcs or fire rainbows are such rare phenomenon to see.

      • The sun must be at an elevation of 58 degrees or greater
      • High altitude cirrus or cirrostratus clouds must be present with ice crystals
      • Sunlight must enter the ice crystals at a specific angle to refract the light

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Final thoughts on what is a fire rainbow

Hopefully you’ve seen a fire rainbow throughout your travels. You may have thought it was just a weird looking rainbow. But, as you see, there’s a bit more science than that of the common rainbow you see after rain when the sun comes out.

What are Fire Rainbows - Always On Liberty

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