Lightning, Canoe Lake: Summer 1915

Tom Thomson and Lightning, Canoe Lake, 1915

There is no question what motivated Tom to complete this sketch. He wanted to record something that was elusive and pure weather – the flash of a lightning strike. The horizon is very near the bottom of the painting leaving no doubt that this is yet another skyscape - weatherscape. 

Lightning occurs with every thunderstorm and is responsible for more deaths than the very exciting, supercellular convection. Science and technology is still learning about the three dimensional shape in space and the four dimensional structure in time of the lightning flash. It is far more complex than meets the eye and I suspect that Tom appreciated that fact. 

Lightning, Canoe Lake, Summer 1915
(21.5x26.7 cm) 8.5x10.5 inches
oils on plywood 
Dr. J.M. MacCallum, Toronto, 1944 bequest
to the National Gallery of Canada

This painting could be looking any direction but the colour in the landscape reveals that Tom had some light on his back. Weather typically  moves from west to east with the jet stream and one can guess that Tom was looking at an approaching thunderstorm passing to his north.  It is less likely that Tom would be painting plein air just after the storm had passed. The lightning and cloud is unobstructed in his painting and this relatively clear view would only be available with the approach of the thunderstorm. After a thunderstorm there is typically an abundance of precipitation fog and mist as well as stratocumulus and SCUD (scattered cumulus under deck). The darker mass that fills the top third of Tom’s panel could be the shelf cloud of the approaching thunderstorm. The shelf cloud immediately precedes the updraft region of most thunderstorms and it is the updraft region generates most lightning. Tom's view is thus likely to be northwesterly.  

The slide from my PowerPoint along with an image of actual
lightning closely resembling what Tom saw and painted. 

The updraft of the convective cell carries small ice particles and their associated, typically positive charge into the higher reaches of the cloud. The cloud top temperatures required to create lightning processes is about minus 25 Celsius. This leaves the cloud base as a negatively charged area. Under the thunderstorm a positively charged “shadow” follows the updraft area trying to connect with the negatively charged cloud base. Short leaders of ionized air channels attempt to make that connection in jabbing strokes both from the cloud down and the land upward. When the connection is completed somewhere between the cloud and the ground, a tremendous amount of energy is exchanged and you do not want to be in its way! If the hairs on your body stand up, crouch quickly on the tips of your toes, become instantly shorter than everything around you and discard everything conductive like gold clubs and carbon fishing rods... 

Kinds of Lightning 

• There are many words to describe the different kinds of lightning. 
• In-Cloud Lightning: The most common type, it travels between positive and negative charge centers within the cumulonimbus cloud. 
• Cloud-to-Ground Lightning: This is lightning that reaches from a thunderstorm cloud to the ground. About one third of lightning strikes hit the ground. 
• Sheet Lightning: This is lightning within a cloud that light up the inside of the cloud like a sheet. 
• Ball Lightning: Rarely seen, this is lightning in the form of a grapefruit-sized, ionized ball, which lasts only a few seconds. 

What can one say about lightning? Lots! Quick Flash Facts: 

• An estimated two thousand thunderstorms are going on in the world right now... 
• There are about 100 lightning flashes around the world every second. 
• The diameter of a lightning bolt is about a half-inch to an inch wide, but can be up to five inches wide.
• The average length of a lightning bolt from a cloud to the ground is three to four miles long. 
• When lightning strikes a beach, the intense heat fuses the sand into silica glass beneath the ground. 
• A flash of lightning appears to flicker because there are usually several bolts of lightning striking at almost the same time. Together they comprise the lightning flash. 
• Flash is comprised of 6 to 8 strokes occurring in less than a second which is too fast for the eye to resolve. This is the reason for the bass sound. 
• Lightning can occur not only in thunderstorms, but also in snowstorms, sand storms, above erupting volcanoes and from nuclear explosions. 
• Electrical current of 10,000 to 100,000 amps far exceed the 15 amps it takes to toast a household fuse. 
• There are 500,000 tonnes (1,000 kilograms) of water in typical thunderstorm. 
• CN Tower gets about 70 lightning strikes each year. 
• 15 Canadians (150 Americans) die each year from lightning. (American are 10 times “better” than Canadians in almost all severe weather statistics.) 
• 40 Canadians (400 -800 Americans) injured each year from lightning 
• Lightning provides half of the world’s fertilizer. The current creates nitrogen based compounds in the air which are delivered to the ground in the precipitation. 
•  Bolt from the blue: A lightning bolt from a distant thunderstorm, seeming to come out of the clear blue sky, but really from the top or edge of a thunderstorm a few miles away.

Thunder is the sound generated by lightning. Lightning bolts are extremely hot, with equivalent temperature of 30,000 Celsius or 5 times hotter than the surface of the sun! When the bolt suddenly heats the air around it to such an extreme, the air instantly expands faster than the speed of sound itself. The shock wave we hear is an explosion of sound. There are 6 to 8 strikes within a lightning flash that lasts a fraction of a second. The frequency of these shock waves is in the lower bass frequency which explains why thunder sounds the way it does. If you are near the stroke of lightning, you’ll hear thunder as one sharp crack since the sound waves will all arrive at your ear at the same instant. When lightning is far away, thunder sounds more like a low rumble as the sound waves reflect and echo off hillsides, buildings and trees. 

This rumbling effect is enhanced if the lightning is oriented along (parallel to) your line of sight. Sound originating along the length will take different lengths of time to arrive depending upon where along that length it originates. Depending on wind direction and temperature, you may hear thunder for up to twenty miles away. Thunder is only a noise and is nothing to be afraid of but lightning is deadly dangerous.

The lightning flash that Tom painted was a negative flash from cloud to ground. The flash was oriented perpendicular to Tom’s line of sight. This means that the sound generated all along the channel arrived at Tom’s ear at about the same time making this particular flash sound like a thunder crack as opposed to a rumble.

There is a lot of wave action so Tom was probably in the gust front portion ahead of the forward flank downdraft of the thunderstorm. Tom also recorded a lot of turbulence and wind in the atmosphere under the base of the thunderstorm. This was quite an active thunderstorm.

The terrain of Canoe Lake would solve exactly where Tom was positioned to record this lightning flash as Tom was very faithful to the scene in front of him. A good guess for Tom’s vantage point would be Hayhurst Point which was one of Tom’s favourite camping places. It is also the location of Tom’s memorial cairn that was constructed by J.E.H. MacDonald and William Beatty.

Tom painted what he saw… Tom's patron Dr. J.M. MacCallum felt the truth and power of the lightning flash and kept this painting on his walls until bequeathing it to the people of Canada and the National Gallery in 1944. 

Frankly we could write another book just about lightning. Although this would be an interesting project as well, maybe it is time to move on.

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”