Tom's Summer Clouds

Summer Clouds, Summer 1916,
Oil on board, 8 1/4 x 10 1/4 in

The challenge of plein air painting is to catch that fleeting moment of inspiration before it vanishes. Capturing the light, colour and essence of a very transient subject in an instant, can be a daunting challenge. This is what keeps artists going out each day to paint en plein air. That challenge is always present. Changes in the subject can bamboozle the finest artist and turn a canvas into an excellent and very colourful fire starter. The Holy Grail is to create a canvas which becomes the artist’s new favourite. 

Tom Thomson was on that quest. He was frustrated more than once. His sketch box was probably hurled into the brush more times than we know. Tom would flick burning matches at his day’s painting efforts. Some of these matches would undoubtedly stick to the wet oils and the colourful flames would release the colours Tom observed and tried to paint, one last time. 

When viewing a plein air work, start with the premise that the sun is on the artist’s back. The harmful UV rays looking into the sun can blind you. If the artist is looking into the sun and especially at sunrise and sunset, they are gazing at the shadowed side of the subject. The shadowed view is back lit, dark and lacking in colours.  With the sun on your back, the artist sees the strong colours of the scene bathed with light.

Summer Clouds, Summer 1916, 8 1/4 x 10 1/4 in

This scene is looking northerly more or less with the sun on Tom’s back. The sun cannot be seen but the greens of the forest are full of colour. The sketch is also another example of a pure skyscape with a very low horizon. The clouds certainly were the subject matter of Tom’s record. 

Cumulus with Significant Turbulence
adding to the lifting of the air parcels

These front lit, cumulus clouds are typical of a fair weather day. The clouds are generated mainly through heating of the earth’s surface and convective lift but there can also be a turbulent mixing component to that lift.  The bases of the cloud become increasing ragged if turbulent mixing and the wind becomes the dominant process to lift those air parcels to saturation. The lifted condensation levels are identical over the landscape and within the same air mass. Note some of the long and level brush strokes over the distant horizon in Tom’s painting. Daytime heating was the dominant lifting process for these air parcels and the timing of this record is probably early afternoon – after lunch. The cloud bases that Tom painted were getting darker suggesting continued lift and greater cloud depths. 

The cloud tops are very white which results from the large number of liquid water cloud drops in the cloud top. These small cloud droplets result from the buoyant lift in the convectively unstable air mass. The clouds are white as a result of Mie scattering which also explains why whole milk is white. A large number of bigger scatterers reflect radiation of all wavelengths basically all directions. Forward Mie scattering is much stronger than the backward scattering and increases as the size of the scatterers increase. Skim milk tends to have a blue tint...

The density of water droplets in a typical cumulus cloud is 0.5 grams per cubic metre. If one does the math, a one kilometre cube of cloud weighs about 550 tons which is similar to the weight of a fully loaded jumbo jet. A typical cumulus cloud is about a cubic kilometre in scale regardless where it might be located vertically in the atmosphere. That is why I included a jumbo jet in my PowertPoint. 

The illumination of the cloud on the left flanks also suggests that this painting was done in the afternoon hours with the sun already past its zenith.  This also fits well with the stage of development in the cumulus. There are too many cumuli to suggest that any are going to develop to the towering cumulus stage. The abundance of cloud blocks some of the daytime heating required for stronger surface based convection. 

The other option to get deep convection requires a short-wave trough in the upper atmosphere and these cannot be observed from the ground until the convection actually occurs. CSI (Creative Scene Investigation) would require the upper air charts from this day to be certain - but there are no short-wave troughs in sight in Tom’s painting!

Vector Addition of the Updraft and the Wind 
Creates the Shape of the Cumulus Clouds
The image of actual clouds reveals the
accuracy of Tom's Record

The shape of the clouds reveals that the brisk wind is from left to right. The prevailing winds with an approaching high pressure are indeed westerly. A west wind in Algonquin during the summer is likely to be a fair weather day. A west wind is also consistent with the cloud shape and a northerly direction of view. 

An exercise would be to match the terrain of a northerly horizon to pinpoint Tom’s vantage point while he painted.

The goal of CSI is to assemble as many puzzle pieces as possible so that they fit together in a consistent picture and story of the record. The more facts available, the more confident one can be in understanding and appreciating the motivation of Tom to record this experience. Tom painted what he saw… 

Warmest regards and keep your paddle in the water,

Phil the Forecaster Chadwick

PS: For the Blog Version of my Tom Thomson catalogue raisonné, Google Search Naturally Curious "Tom Thomson Was A Weatherman - Summary As of Now" or follow this link “http://philtheforecaster.blogspot.com/2022/10/tom-thomson-was-weatherman-summary-as.html”