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What you need to know about COVID-19: August 12, 2020
Last Friday evening, the weather was – to quote a Caper I know – not fit!
Around the supper hour, an active warm front came through the Halifax area, changing snow to rain; the wind was wild – gusting over 100 km/h. The temperature shot up to 11 C in less than an hour. I was out in it, and it felt very strange. I didn’t see anything unusual until I returned home and checked my social media channels. People who were out in it witnessed an amazing sky – a purple sky.
This email was one of many I found in my inbox:
“We have a question for you and I hope you can explain what it was that we saw. On Friday, Feb. 7 around 6 p.m., the fog outside our apartment building overlooking Hwy 102 in the Larry Uteck area was very thick and just before the heavy rain and very strong winds began, we saw the fog turn into a pinkish-purple colour. I went to the other window to make sure we weren’t imagining things. Needless to say, it was very alarming. Shortly after seeing the colour of the fog, the wind slammed against the building with a very loud bang and the rain began pouring. The fog simply disappeared once the rain started. Do you have any idea why the fog was that colour?”
Hazel and Wayne
A purple sky during a powerful wind and rainstorm is the result of a perfectly natural occurrence called Rayleigh Scattering. In the air, scattering of light by molecules of oxygen and nitrogen in the atmosphere makes the sky blue. But the magical purple colour from wind and rainstorms can form when the air is supersaturated with moisture, and the storm clouds hang low in the sky.
On Friday, the sky was saturated, and the moisture in the atmosphere refracted the light of the setting sun. Normally, only the longest wavelengths of light on the colour spectrum are visible through the clouds – that’s why sunsets often appear gold, pink, and orange. Violet is the shortest wavelength on the spectrum, which means it’s almost never visible in the sky. But the air’s high moisture content Friday evening, combined with the dense low-hanging clouds, created the perfect conditions for a rare purple sky.
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Cindy Day is the chief meteorologist for SaltWire Network