Lightning

Lightning southwest of Brandon, MB. Summer 2000. Photo: Dan Lewis (Black Tree Photography)

Thunder is the noise caused by the explosive expansion of air due to the heat generated by a lightning discharge. Thunder may have a sharp cracking sound when lightning is close by, compared to a rumbling noise produced by more distant strokes.

Because light travels at a faster speed than sound, you can see a lightning bolt before the sound of thunder reaches you.

To judge how close lightning is, count the seconds between the flash and the thunder clap. Each second represents about 300 metres. If you can count less than 30 seconds between the lightning strike and the thunder, the storm is less than 10 km away and there is an 80 percent chance the next strike will happen within that 10 km. If you count less than 30 seconds, take shelter, preferably in a house or all-metal automobile (not a convertible top) or in a low-lying area.

Lightning may strike several kilometres away from the parent cloud and precautions should be taken even if the thunderstorm is not directly overhead.

Learn the 30-30 rule

• Take appropriate shelter when you can count 30 seconds or less between lightning and thunder.
• Remain sheltered for 30 minutes after the last thunder.

If caught outdoors:

• Keep a safe distance from tall objects, such as trees, hilltops, and telephone poles.
• Avoid projecting above the surrounding landscape. Seek shelter in low-lying areas such as valleys, ditches and depressions but be aware of flooding.
• Stay away from water. Don't go boating or swimming if a storm threatens and land as quickly as possible if you are on the water. Lightning can strike the water and travel some distance from its point of contact. Don't stand in puddles even if you are wearing rubber boots.
• Stay away from objects that conduct electricity , such as tractors, golf carts, golf clubs, metal fences, motorcycles, lawnmowers and bicycles.
• Avoid being the highest point in an open area. Swinging a golf club or holding an umbrella or fishing rod can make you the tallest object and a target for lightning. Take off shoes with metal cleats.
• You are safe inside a car during lightning , but don't park near or under trees or other tall objects which may topple over during a storm. Be aware of downed power lines which may be touching your car. You are safe inside the car, but you may receive a shock if you step outside.
• In a forest , seek shelter in a low-lying area under a thick growth of small trees or bushes.
• Keep alert for flash floods , sometimes caused by heavy rainfall, if seeking shelter in a ditch or low-lying area.
• If caught in a level field far from shelter and you feel your hair stand on end, lightning may be about to hit you. Kneel on the ground immediately, with feet together, place your hands on your knees and bend forward. Don't lie flat.
• If you are in a group in the open , spread out, keeping people several yards apart.

Indoor Precautions:

• Before the storm hits , disconnect electrical appliances including radios and television sets. Do not touch them during the storm.
• Don't go outside unless absolutely necessary.
• Keep away from doors, windows, fireplaces , and anything that will conduct electricity, such as radiators, stoves, sinks, and metal pipes. Keep as many walls as possible between you and the outside.
• Don't handle electrical equipment or telephones. Use battery operated appliances only.