Rainbows are quite common, but mostly during our warmer months. Perhaps that’s why Karen Lannan decided to drop me a line after she spotted what she described as a cloud bow in the Cobequid Pass area of Nova Scotia just a few days before Christmas.
A cloud bow sounds pretty but what Karen saw was in fact a snowbow, a cousin of the more popular rainbow.
We’ll start with the rainbow.
A rainbow can only occur if there are raindrops in the air – as they are caused by the refraction and dispersion of the sun’s light by rain or other water droplets in the atmosphere.
It was cold enough to have flurries in the air when Karen spotted her “bow” but there also had to be some liquid moisture in the air, that had not yet frozen.
You see, snowflakes just don’t cut it. Snowflakes are beautiful, incredibly complex, six-sided branched crystals; each one is different, but they cannot form a “snowbow.” Snowflakes are often aggregates or a collection of multiple snowflakes all clumped together as they fall from the sky. Light refracts off of these more randomly and so the wavelengths are not scattered out in an orderly fashion. Rainbows need spherical raindrops. Sunlight enters a drop, refraction changes the light’s direction, and it bounces off the sphere’s opposite side before leaving the drop.
In the photo Karen took, it doesn’t appear to be snowing or raining but there has to be some moisture droplets in the air to split the light into a pretty bow.
Imagine seeing a rainbow during a snowstorm? It’s possible, especially along coastal areas. When it’s not too cold out, small raindrops occasionally accompany snow and could form a rainbow that shines through the snow.
No word on whether Karen tracked down the elusive pot of gold…
If you come across something unusual and would like to know more about it, snap a photo and send it to me at: [email protected]. I’ll do my best to explain it.
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Cindy Day is the chief meteorologist for SaltWire Network
