Dark Thunderheads

It might not be obvious but this is an example of supercellular convection. “Dark Thunderheads” was probably as close a description of supercells as one can expect from those unfamiliar with meteorology. Tom was motivated to record this weather event as it was certainly marked by nearly continuous thunder and dramatic wind shifts. Tom had a northerly view as the clouds are clearly front lit and there was some colour to be seen in those distant ridges even under the shadows of the towering thunderstorms. 

Storm Clouds, Algonquin Park or Dark Thunderheads
or Storm Cloud Spring 1916 or Lake & Lowering Sky.
Oil on composite wood-pulp board 8 7/16 x 10 9/16 in. (21.5 x 26.8 cm).
R.A. Laidlaw Thomson Collection at the Art Gallery of Ontario

Tom was quite close to this supercellular cumulonimbus cloud and was unable to fit it on to his 8.5 by 10.5  inch panel – even with the horizon placed so very low on his panel. As a result he painted the portion of the storm that interested him most. 

An Excellent Conceptual Model of the Supercell Thunderstorm

For a supercell, this happens to be the flanking line with the main updraft to the right side of the image.  The underside of the upstream anvil was barely hinted at but to a meteorologist, the large, back-sheared anvil is key to the successful application of Creative Scene Investigation, CSI.  An anvil that spreads upstream reveals that the updraft was very strong and associated with significant  wind shear. Wind shear is essential to generate a rotating supercell but that is another course in meteorology.

Graphic from my PowerPoint Showing the Portion of the
(Dark Outlined Box) Supercell Included in Tom's Weatherscape

The updraft was painted like a “barber pole” indicative of the rotating updraft. This is especially evident when one examines the original painting. Long and bold strokes of the brush alternate upward following the updraft just like the alternating colours of a barber pole. It is certain that Tom witnessed the rotation of the updraft which in itself is the fundamental definition of a supercell.

There could be a series of these thunderstorms toward the north suggesting possible organization along a squall line. However it is challenging to be certain from Tom’s painting – I suspect there is only the one supercell but can’t be sure. A lone, rogue supercell is actually more likely to be accompanied by severe conditions. This severity results from the fact that a single cell is able to access all of the heat and moisture energy in the air mass and convert that into motion. 

Top Down View of Supercell Thunderstorm
Conceptual Model 

The scud (Scattered Cumulus Under Deck) cloud in Tom’s painting is problematic. Remember that scud is formed when rain moistened air is lifted to form cloud at a level below the lifted condensation level for the air mass - the deck. This scud is certainly along the gust front from the rear flank downdraft which moved in after Tom started to paint. Thus the scud cloud appearing in the painting was purely a result of timing. Notice the scud cloud has no uniform base and is formed in the chaotic wind around the supercell and in the heavy rainfall. Tom had no choice but to paint the reality of what he witnessed, leaving it up to us to interpret those observations as best as we can. The scud cloud did hide the details of the flanking line that we know must be there feeding into the updraft. 

Notice that there was a considerable amount of wave action on the lake. There is not a clear enough signal to deduce a wind direction from those water surface gravity waves. However from the location of the updraft and knowledge of the wind profile that occurs around supercell thunderstorms, Tom would have been enjoying a warm if not hot and blustery southwesterly wind on his back when he started to paint. This wind would have shifted dramatically to the west and then northwest with the arrival of the afore-mentioned cooler, gust front winds. The gust front would have also brought the turbulent scud cloud. 

These intense and dynamic supercells are typical of spring and early summer. They are dominated by strong convective energy and wind shear. Supercells tend to be large beasts and thus Tom was able to stay south of the rain while still recording the weather observation. 

In some performance measurements studies I conducted while with Environment Canada, I detected a strong signal that La Niña years of the El Niño–Southern Oscillation (ENSO) climate pattern, were very conducive for supercell convection. The La Niña event that developed in the spring of 1916 and lasted until the spring of 1918 was the 13th strongest of the ‘classic’ La Niña events. It should not be surprising that Tom observed and painted a lot of severe convection during this period when he was at the peak of his artistic expression and tragically, the end of his career.

Singleton Lake Supercell

 Note that there was only one obvious “thunderhead” in Tom’s painting and not more as suggested by the title. The scud cloud was not a cumulonimbus cloud.  The accompanying image depicts the portion of the supercell that Tom recorded on his rather small panel using a photo of a supercell thunderstorm that I observed at Singleton Lake.  

The Singleton supercell was almost an identical twin to Tom's supercell. There was even some scud cloud that drifted into my view-finder at just the right moment but it was not nearly large enough to obscure the flanking line of the storm. All of the observations that I made of Tom’s painting, apply equally well to my photograph. This supercell had already knocked down several swaths of very large trees and cut power to the area. Our laneway was blocked by some large trees that had been felled by the damaging, downburst winds. Supercell thunderstorms can be lethal and are best viewed from a distance - preferably on radar or satellite imagery. 

This painting has been given several different names including Storm Clouds, Algonquin Park; Autumn Woods and Lake; Storm Cloud Spring 1916; Lake & Lowering Sky; and the name I preferred “Dark Thunderheads”. All of these titles miss the mark.  I would suggest that the name of this painting should be "Supercell with SCUD". This explains why I am very careful in naming my art and telling the story behind each individual painting. I also typically discus the nature and science revealed in the scene. I do all of this to eliminate the need for someone like me, making it all up years later. 

Tom painted what he saw… This painting may be viewed as part of the R.A. Laidlaw Thomson Collection in the Art Gallery of Ontario. Pay close attention to the long, bold and overlapping "rotating updraft strokes".

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”