Struck By Lightning

We are rather susceptible in Canada. Our country is mostly landscape, and we’re often roaming around it, beyond broadcast areas, beyond cover. To prepare ourselves, we have to be our own Environment Canada: we have to learn the rudiments of storms, know the terrain we’re travelling through, be able to tell a front from a squall line, a stratus cloud from a nimbus. Thunderstorms do give notice — wickedly short, usually, but always distinctive. After my brush on Georgian Bay, I boned up, taking myself to the You and Your World shelf at the library.

Storms rely on the rapid, sustained uplifting of air, especially warm, moist air. This is why they occur frequently in summer, when the ground has grown hot by late afternoon. Open fields heat faster than forests or water, rocky slopes faster than ground covered by vegetation; hence the sudden onrush of the storm we experienced, parked on the warm rock enfolding Georgian Bay, just at cocktail hour at the end of a hot day.

Convection fuels thunderstorms, either from warm air rising off the ground, or from a drop in temperature in the atmosphere. Cheery, popcorn white clouds in the sky mean unstable air has stopped rising and has reached the dew point, when its temperature equals that of the surrounding air. These cumulus clouds can persist for days or they can dissipate, but if warm thermal air keeps pushing up, they often develop into cumulonimbus clouds. When this happens, an aerial game of pinball begins. Droplets bounce around, collide, pick up grit, old volcanic ash, the detritus of life below, all of it freezing into ice crystals in the troposphere. Air travellers experience this as turbulence, their plane passing through cumulonimbus clouds, lurching in the chaos, the cabin windows dashed with rain or hail, until the aircraft emerges from the cloud.

On the ground, this intense interior action looks like a change from roly-poly clouds jogging in the sky to clouds darkening and mounting into towers. This formation means a storm is brewing. Inside the cloud, ice crystals and raindrops zing about in all directions, slamming into and fusing with one another, growing larger and heavier, until they start falling through the cloud as rain or snow or hail.

Lightning gets into the action through an electrical charge that builds during these high-wire collisions. When a beauty of a storm is brewing, a negative charge heats up at the base of the cloud. The earth’s surface tends to be negatively charged, and since like charges repel, current at the bottom of the cloud draws away from the ground, leaving a positive charge in the air. This is that pre-storm sense one gets, the hair on the head lifting slightly, the air freighted with electricity.

It’s in the nature of air to act as a buffer, to resist electrical flow, and for a time it contains the mounting charge. But it can’t hold out forever. At a certain point, the negative charge from the cloud expends itself, not all at once, which would be an atomic reaction, but haltingly, in a “stepped leader” about as thick as a pencil. This negative charge gropes toward the ground, moving in a searching way, like a lonely drunk in a bar looking for a connection. Eventually, it attracts a positive charge from something tall on the ground — a tree or a tower, a farmer on a tractor. When lightning strikes, the charges have connected in a streamer, a flood of positive current that surges back up into the cloud, spectacularly hot, so intensely superheating the surrounding air that a shock wave bulges out, faster than the speed of sound.

Thunder is the sonic boom we hear when the percussive force breaks the sound barrier. Once the stepped leader from the cloud locks to the streamer from the ground, a channel opens for pulses of electricity to pass through, producing several flashes. We see the lightning before we hear the boom, but the thunder actually occurs first; the speed of light outraces the sound of thunder to our senses.

In its defence, lightning is only doing its job. It’s the celestial housekeeper, balancing an overcharged heaven and earth.

I am standing on the north shore of Lake Superior beside my kayak, debating whether to make the twelve-kilometre crossing to the Slate Islands. The steep spruce hills on the islands are criss-crossed with caribou trails, and the wild, broken beaches on the south side face an infinity of sky and water. I’m alone, a competent paddler used to solo travel, vigilant and informed about the genesis of storms, and I’m longing to go. In the morning, I tune in to a broadcast: there’s a storm watch in effect. Driving up the day before, I noticed the blue sky beginning to sprout low cumulus clouds. Today the clouds are more altocumulus, mid-level, joined like loaves of bread. The sun is shining, but the sky to the west has a purple tinge, and a wind is gathering. It’s the height of summer. If there are clouds in the morning, an afternoon storm is a probability. Do I have time to cross?

Paddling at six kilometres an hour, I need two hours when I’m not in the storm radius and not the tallest object in this watery field. I’ve almost decided to chance it when I glimpse a flash of lightning, lovely and silent on the violet horizon to the west. There’s no thunder, which means the storm is at least sixteen kilometres off, but that’s no comfort. Lightning is so volatile it can easily strike ahead of the thunderheads from that distance. Another flash, with time-delayed thunder following. I apply the old “flash-bang” guideline, count the interval between seeing the flash and hearing the bang, divide my count, in this case twenty seconds, by five, and calculate that the storm is four miles, or six kilometres, away. I wait and count the next round, with the same result. This could mean the storm is stalled, but it might not. I glance at the enticing bulk of the Slates across the channel and know I’m not going. I’ll have to wait until whatever is coming has passed.