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Ask 2 Weather: Is a “hailbow” a real thing?

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HOUSTONAt KPRC 2, we’re dedicated to keeping Houstonians informed. As part of our new Ask 2 series, the newsroom will answer your questions about all things Houston.

The question: Is a “hailbow” a real thing?

The answer: This question was posed by a viewer who, at the time, was reading a book to a group of 7th graders. One of the characters referred to a “hailbow” and the viewer wanted to know if they are real. Indeed, hailbows produced from hailstones are possible, but raindrops are much more likely to produce rainbows. To understand why, let’s discuss the basic science of rainbows.

Rainbows and hailbows are created the same way. The same physics applies to both. They form when sunlight refracts, reflects and disperses while passing through a droplet of water (or ice). The water acts as a prism. It has a different refractive index than air. When the light enters a droplet, its path is bent at an angle. More specifically, each color (or wavelength) of light bends at a different angle. This causes the rainbow (ROYGBIV) effect. The diagram below, courtesty of NOAA SciJinks, shows the process.

Refraction, reflection and dispersion of sunlight in a water droplet to form a rainbow.  Image courtesy of NOAA SciJinks
Refraction, reflection and dispersion of sunlight in a water droplet to form a rainbow. Image courtesy of NOAA SciJinks

Light is refracted as it enters a water droplet. It is then reflected off the back side of the droplet. Finally, it is refracted again as it translates out of the droplet and back into the air. When you are viewing a rainbow, you are seeing the refracted, reflected and dispersed light bouncing back at you from a the raindrops or hailstones.

Here is an interesting side note: Because of how a rainbow forms, you will only be able to view a rainbow when the sun is at your back!

Rainbow formation.  Image courtesy of NOAA SciJinks
Rainbow formation. Image courtesy of NOAA SciJinks

NOAA SciJinks explains the process in further detail and is a great resource for students looking to understand the science.

Now, let’s get back to the question of rainbows forming in hailstorms. Because light has to pass through a water droplet or ice pellet in order to form a rainbow, the water or ice has to be clear so that light can transmit through it easily. Water droplets are almost always clear and colorless and are great for producing rainbows. Hailstones are not. Hailstones can be clear and colorless, milky white or completely opaque -- much like ice cubes in your freezer. Those that are clear can easily allow light to pass through and would be great hailbow producers. But those that are milky white or completely opaque don’t easily allow light through and, therefore, would not produce a hailbow.

Here is another example of how ice particles create a rainbow effect: Cirrus clouds, made up of tiny ice particles floating high in the atmosphere, often refract and reflect visible light to form a halo around the sun or moon.

Halo around the sun created from the refraction and reflection of light by ice crystals in cirrus clouds.
Halo around the sun created from the refraction and reflection of light by ice crystals in cirrus clouds.

Do you have a burning H-Town-related question? Send it our way, and we will try to hunt down an answer.

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