Tuesday, July 24, 2018

Weather Wisdom: Yellow streaks in a sunset sky, wind and daylong rain are nigh.

Wisdom can be found in the natural world. We just need to look. Elly MacKay’s “Red Sky At Night” returns us to our rural roots. There is no need for technology. There are no equations. Simple scrutiny of nature can lead to understanding the important processes at work in the world. Some of these ancient poetic weather observations are treasures supported by modern science. Some are simply nice poems. Both are fun.
 Elly MacKay's "Red Sky At Night"
Published by Tundra Books you can find Elly MacKay’s book at this link.

One piece of weather wisdom that Elly examines is …
Yellow streaks in a sunset sky, wind and daylong rain are nigh. 

True. Cirrus clouds look like “yellow streaks” at sunset. The Latin name for these clouds mean wispy hair, which is just what they look like. These clouds are a sign of changing weather. “Nigh” in this saying means coming soon. Excerpted with permission from Elly MacKay’s Red Sky at Night (published by Tundra Books, 2018).

Yes, this is my favourite weather rhyme and very true. Those cirrus cloud lines in the sky are called deformation zones and they tell of the approach of a storm. At sunset you are looking westerly and those high cirrus clouds behind the deformation zone are coming your way. 

Deformation zones are always associated with a current of air and their characteristics reveal everything about the weather. Think of this particular current as a rising conveyor belt transporting warmth and moisture to the north. This southerly current of air follows a high pressure area while it precedes a low. Fair weather with the high must be replaced by stormy weather with the low. 

Observers of a warm conveyor belt which is the yellow diverging arrow in the above drawing, will first see the leading edge of thin cirrostratus high in the atmosphere. As the transport of heat and moisture continues this cloud will thicken behind a lower level deformation zone. Nimbostratus and rain will follow behind an even lower deformation zone when the warm conveyor belt completes its delivery of moisture. 

The image below is looking eastward at the same warm conveyor belt. The clouds on the right are a real life example of the scientific graphic on the left. I took that picture looking upward at the approaching layer of clouds from the approximate location of Phil’s green eye in the left portion of the image.
The deformation zone lines in the sky result from the stretching of the air between the opposing circulations around the high and low. The accompanying graphics hopefully saved a lot of words.
In actuality the deformation zone lines are just where quasi-horizontal layers of moisture intersect the three-dimensional skin that encapsulates the mass of air. That warm and moist air is being transported to the north as part of the energy balance of the earth. More on this later…

The atmosphere is a fluid like any other substance that flows. One can create your own deformation zone using a paddle to create a current (jet stream in the image below) in a pond. The leading edge associated with this flow is a deformation zone made obvious by the contrast between the open water and the duck weed. 

Yellow streaks of deformation zone cirrus foretell of the moisture being transported to your location by the warm conveyor belt of a storm. There is a lot of very fine science in a little prose. 

In fact art is science and science is art. I have painted a lot of deformation zones and have turned those into a science on which I based my 36 year career with Environment Canada. The weather is your friend. 
 For this and much more art.
My thanks to Elly MacKay, Tundra Books, Penquin Random House and COMET (for the scientific graphics) where I finished the last decade of my career publishing meteorological training modules. 

I am thinking of explaining the science behind more of the weather wisdom sayings as time permits. 

Phil the Forecaster Chadwick

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