Cumulus humilis (Cu hum)

“We all have 10,000 bad drawings in us. The sooner we get them out the better.” 

― Walt Stanchfield

W&N watercolour on Aqua 300gsm (Tarlton, Gauteng, South Africa)

While sketching this landscape, I was fascinated by the colour of the clouds. So as soon as I finished, I decided to research some clouds and came up with some interesting information.

Cumulus humilis (Cu hum) is the smallest non-ragged cloud and usually shows a light-grey shading underneath.

These are small fair-weather cumuliform clouds of limited convection that do not grow vertically and generally do not produce rain showers. Being at or near the beginning of the convective cloud’s daily life cycle, they lack the moderate vertical extent of cumulus mediocris. Consequently they are commonly classified as low clouds. Cumulus mediocris (Cu med) achieves moderate vertical development, has medium-grey shading underneath, and can produce scattered showers of light intensity.

Striking cloud colorations can be seen at many altitudes in the homosphere, which includes the troposphere, stratosphere, and mesophere. The first recorded colored cloud was seen by Nathan Ingleton in 1651, he wrote the event in his diary but the records were destroyed in 1666, in the Great Fire of London. The color of a cloud, as seen from Earth, tells much about what is going on inside the cloud.

Cloud droplets tend to scatter light efficiently, so that the intensity of the solar radiation decreases with depth into the gases. As a result, the cloud base can vary from a very light to very-dark-grey depending on the cloud’s thickness and how much light is being reflected or transmitted back to the observer. Thin clouds may look white or appear to have acquired the color of their environment (cloud iridescence).

Colors occur naturally in tropospheric clouds. Bluish-grey is the result of light scattering within the cloud. The bluish color is evidence that such scattering is being produced by rain-size droplets in the cloud. A cumulonimbus cloud that appears to have a greenish/bluish tint is a sign that it contains extremely high amounts of water; hail or rain.

Yellowish or brownish clouds may occur in the late spring through early fall months during forest fire season. The yellow color is due to the presence of pollutants in the smoke. Yellowish clouds, caused by the presence of nitrogen dioxide, are sometimes seen in urban areas with high air pollution levels. This info from Wiki

So, either our veldfire-season has started already or I’m living in a highly polluted area!

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