Irridescent Rainbows Among The Clouds
Janice Rae Pariza
Photograph - Photography
We've been getting several reports Wednesday afternoon of "rainbows in the sky" or clouds that are brilliant colors.
They're givien the coloquial name of "fire rainbows" and they are due high, wispy clouds that are made of tiny ice crystals, and if the cloud is at the right angle to the sun, the crystals will refract the sunlight (much like a prism) into the colors of the rainbow.
So it's very similar to a regular rainbow-when-it's-raining, only a little more rare.
These fire rainbows are rare sights in the mid-latitudes, because they can only occur when the sun is 58 degrees or higher above the horizon. For the United States in general that pretty much relegates any sightings to roughly around 6 weeks either side of the summer solstice.
This photo was taken in Ouray, Colorado at around 1PM facing South.
Local weather lore is that when you see these types of rainbow clouds or a rainbow halo around the sun, it's a signal that rain is coming within 24 hours as these cirrus clouds typically come ahead of an approaching cold front.
But just like Punxsutawney Phil isn't right every year, rain in the short term is not the case this time. These are just some high clouds drifting in from offshore. Still no rain in the forecast.
Sky watchers on occasion report seeing colors in the clouds, and sometimes our friends send photos of these rainbow colors in clouds. You�ll find some examples below. These colorful clouds are called iridescent clouds, and the phenomenon is called cloud iridescence or irisation. The term comes from Iris, the Greek personification of the rainbow. It�s similar to the colors you might see when oil lies on the surface of a puddle of water. When you see a cloud like this, you know there are especially tiny ice crystals or water droplets in the air. Larger ice crystals produce solar or lunar halos, but tiny ice crystals or water droplets cause light to be diffracted � spread out � creating this rainbow-like effect in the clouds.
Bottom line: You might on occasion see a rainbow-like cloud. They are fairly rare. They�re caused by the presence of tiny ice crystals or water droplets in the air, which cause light to be diffracted or spread out.
August 1st, 2013
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