Tom Thomson's Burnt Land at Sunset

 

What was Tom’s motivation to “record” this particular observation? I sincerely doubt that the backlit skeletons of trees and the shadowed forest and hills were what attracted Tom's attention. I suspect that Tom was mesmerized by the colours and structures in the sunset sky. He was also possibly fascinated by the rapid motions of those cirrus clouds with the jet stream and the dramatic dissipation of the cumulus in the warmer air south of the jet stream. Please let me explain. 

Burnt Land at Sunset Summer 1915
oil on wood-pulp board
height: 21.6 cm (8.5 in); width: 26.7 cm (10.5 in)
(Tom's Paint Box Size)
Collection of the Art Gallery of Ontario

The title assumes that the burnt trees were what attracted Tom’s attention and that the low horizon was just a by-product of that composition. The following meteorological discussion will reveal that it was the dynamics of the weather that drew Tom to this scene. – so to speak.

Sunset colours in the sky confirm that this sketch was indeed an evening painting. That portion of the title is certainly appropriate and useful. The forest and trees were backlit and dark so the sun had already set although it still illuminated the sky. The brighter part of the sky was on the left side of the panel revealing the location of the sun and that Tom must have been looking westerly - more or less. One can fine-tune this direction by adjusting the location of the sunset to the season - more southwest in the winter and more northwest in the summer.  There were no leaves on the burnt trees (humour intended) so this was possibly a late autumn or even a spring “record”. The purple hues in the lee of the forest actually look like snow on the ground to me. "Summer" is used in the title but I am not convinced as Tom would have likely been fishing. 

Cirrus, cumulus and stratocumulus can all be found in this weather mix and each requires special investigation. 

Jet Stream Cirrus with Gravity Wave Billow Clouds

The structure of the white and high cirrus indicates a strong jet stream blowing from the southwest toward the northeast. The overall linear structure of the cirrus is certainly the result of a jet stream as opposed to a deformation zone. Meteorologists typically refer to this cloud as "jet stream" or "baroclinic zone" cirrus. The jet stream is the lofty result of the contrasting temperatures found across a frontal system. 

The additional clue is the transverse type banding of the cirrus directed laterally to the elongated jet stream cirrus. This gravity wave cloud structure is often called “billow cloud” and it is highly correlated with stronger jet stream winds and clear air turbulence. The transverse banding also indicates that the jet stream was strong with speeds in excess of 120 knots. This will not be on the quiz. 

The other cloud in Tom's composition was certainly backlit low cloud with bases well below 6500 hundred feet above the ground. The cloud fragments in the foreground appear distinctly different from those in the distance. 

Cumulus Fractus - Cumulus cloud dissipating into fragments 
with the setting sun. PowerPoint slide from the presentation. 

The cloud in the foreground was cumulus fractus that was dissipating with the setting sun. Convective cumulus clouds typically require daytime heating of the ground to ascend.  These bubbles of warm air stop rising as the sun sets so the convective bubbles are disorganized and only fragments of their former selves. I am troubled that it is still illuminated by the setting sun but this could reflect the time it took for Tom to record his observation. This cumulus cloud would be appropriately located on the warm or southern side of the frontal baroclinic zone. It would also be located south of the upper jet stream in this scenario. The cumulus cloud on the warm side of the jet stream is a result of the warmer, more moist and more unstable air mass to be found there.

Stratocumulus Cloud on the Cold side of the jet stream.
PowerPoint slide from the presentation. 

The low cloud bank in the distance was stratiform and stable. This layer of stratocumulus was on the cold side of the upper jet. Daytime heating is not as effective in creating a cumulus cloud in the cloudier and colder air mass which is comparatively more stable.  Subsidence was also likely occurring in the cold air mass with the approach of the ridge of high pressure. Subsiding air must warm as the pressure increases and the resulting higher temperatures are an obstacle to rising thermals. The associated subsidence inversion would thus create a strong cap on top of the stratocumulus clouds causing them to flatten out.

The three distinctly different cloud types allow us to confidently locate Tom Thomson within the weather pattern of the sunset sky. Tom was at the green circle in the following graphic, looking in the direction of the green arrow.

PowerPoint Slide from "Tom Thomson Was A Weatherman

This interpretation of the jet stream and cloud types and their relative positioning is completely consistent with their interrelated meteorology and the associated air masses. Seeing is believing and a meteorological friend created the following time-lapse video of a situation very similar to that which inspired Tom Thomson. 

The accompanying graphic  further explains what is revealed by the video.

We live at the bottom of the atmospheric ocean. The weather 
is always an inspiration and I believe that Tom witnessed weather
similar to that displayed in the time-lapse video. 

The pinks and oranges of the sky also indicate that the atmosphere was not overly moist. If the air mass had been moist between the scene and the western horizon, the clouds would have been tinted a stronger red colour. The sky itself was relatively clear blue. 

Tom's location (yellow star) within the parade of weather systems.
 A cold front might have passed by a day or so earlier but a ridge
of high pressure would bring fair conditions for the next few days. 

Note that the next day was going to be a repeat performance of that particular day although eventually, the jet stream would guide a low-pressure area across that location. Tom could have expected a storm in a few days. 

Tom did not sign or name this painting as was his custom for his plein air weather observations. Upon his passing in July 1917, this painting of dynamic weather entered his estate and changed hands a few times before ending up in the Thomson Collection of the Art Gallery of Ontario. Apparently, this work did not previously catch the eye of Dr. J.M. MacCallum (1860-1943) in which case it probably would have ended up in the National Art Gallery of Canada. 

Tom painted what he saw and the thrill of the chase and the challenge of recording the weather  was enough for him. 

Warmest regards and keep your paddle in the water,

Phil Chadwick

PS: Tom Thomson Was A Weatherman - Summary As of Now contains all of the entries to date.