Perhaps the coolest clouds in the world

I get a lot of mail, Facebook posts and messages. Not all start with “I have never seen anything like this in my life." That's how Corrine Kean framed her introduction, and it certainly got my attention.

The series of photos that followed was stunning. One recent evening, Corrine looked up from her backyard near Shelburne and saw streaks of colours like none other.

Clouds come in all shapes and sizes, and just when you think you've seen them all, you come across cloud iridescence.

Cloud iridescence is a rare phenomenon usually seen in altocumulus or high cirrustype clouds. The colours in the cloud are similar to those seen in oil films on puddles after it rains. The lovely display can also be described as cloud irisation; that term comes from Iris, the Greek personification of the rainbow.

Here's what happens.

When parts of clouds are thin and have similar-sized droplets, diffraction can make them shine with stunning colours. These colours are displayed in random patches or, in this case, more striking and uncommon bands. Iridescence occurs in an area of the cloud where all the droplets have a similar history and a similar size.

Because these pretty pastel patches are often in the vicinity of the sun, they can be hard to see. It's never a good idea to stare directly into the sun, so the best way to see an iridescent cloud is to place the sun behind a foreground object, like a building.

Look up, but always remember to protect your eyes!

WEATHER BY DAY

Cindy Day is chief meteorologist for Saltwire Network.