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Spokane, Washington  Est. May 19, 1883
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News >  Idaho

Weathercatch: Somewhere over the fogbow, sun or moonlight shines

By Nic Loyd and Linda Weiford For The Spokesman-Review

Fogbows, also known as rainbow ghosts, are a work of art by Mother Nature that appear this time of year. Though not as well known or showy as rainbows, these arched ribbons of milky-white light inspire their own quiet beauty.

Fogbows are most common in fall and winter when radiation fog tends to develop. Where a rainbow forms when sunlight shines through raindrops, a fogbow is created when sunlight cuts through the fine mist that makes up fog. Fog’s tiny water droplets – much smaller than raindrops – act as miniature prisms that scatter the light waves and diffuse any colors.

According to NASA, its ghostly hue is caused when a “quantum mechanical wavelength of light smears out the colors that would be created by larger rainbow drops.”

Because fogbows need a combination of cool air, fog and sunlight to form, they’re more commonly seen among hills and mountains, ocean mists and in the Arctic. Here in Washington, they make occasional appearances this time of year when cold temperatures, lingering moisture near the ground, calm winds and somewhat clear skies converge.

Then, two more things are needed in order to see one: The sun must be behind you and the not-too-thick fog in the front. The same goes at night when fogbows are illuminated by a bright moon or a vehicle’s headlights.

Chances are, fogbows are around us more often than we think. The reason we don’t see them is because the angle from where we happen to be isn’t correct. Should you see one, consider yourself lucky and snap away with your smartphone or camera.

Supposedly there’s a pot of gold at the end of a rainbow. Could there be a pot of pearls at the end of a fogbow? Unfortunately, by the time we arrive at what appears to be the end of a fogbow, all those just-right angles and precise ingredients of water droplets and light would shift, leaving no pot of pearls in sight.

Instead, the elusive, ghostly white arc would have to stay imprinted in memory.

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Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact: ldweiford@gmail.com.

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