When you see large, dark flat clouds beginning to cover the skies, get set to watch the show – celestial fireworks.
The best time to watch a lightning show is at dusk, when it is light enough to see the contours of the clouds yet dark enough to appreciate the light sparks and flickers. Look for the earliest flashes near the top of the thunderclouds; then observe as the flashes move deeper and deeper into the cloud.
As you watch the storm (hopefully from inside the comforts of your house), you will witness the most powerful light source in nature, carrying enough energy to power 20,000 toaster ovens. Following the light, you hear the crack and rumble of thunder – the shock wave of air exploding in the 27,000 degree Celsius heat of the flash.
How Lightning Forms
Lightning forms when positive and negative charges become separated. The positive charges stay near the top of the large, flat-topped cloud, while the negative charges accumulate near the bottom. When the cloud’s bottom charge becomes strong enough, a flow of electricity zigzags down toward the ground. This flow of energy is not the lightning stroke, however. Barely visible and lasting only a microsecond, this is called a stepped leader. Because opposites attract, positive charges from the ground come racing towards the negatively charged stepped leader. The region of positive charge moves up through any conducting objects in the area, including trees, electrical wires and people. It is this brilliant return stroke, coming from the Earth to the sky, that closes the electrical circuit, causing the celestial fireworks of lightning. The flash appears to be going down because it retraces the downward-forking path of the stepped leader. What seems to be a single flickering flash is actually often a dozen or more strokes, each one only ten-thousandths of a second long, in the same path.
The sounds of lightning come a few seconds after the light because sound travels slower. The closer the lightning, the more rapid the report of the thunder. Light travels at 300,000 km/sec whereas sound travels at 0.3 km/sec. You can calculate the distance of the lightning strike. After the flash of lightning, begin counting off the seconds until the thunder is heard. Divide the seconds by three to arrive at the distance in km.
Canada averages over 2 million lightning strikes are each year. And, despite our relatively short lightning season, 9 to 10 people are killed and between 100 and 150 people are injured each year by lightning in Canada. This compares to an average of 57 deaths per year in the United States. To stay safe, the best place to be is Inside a house which has plumbing and wiring or an all-metal vehicle (not a convertible). Stay away from electrical appliances and equipment, doors, windows, fireplaces, and anything else that will conduct electricity, such as sinks, tubs and showers. Picnic shelters, dugouts, small buildings without plumbing or electricity are NOT safe.