Presented by VE3LXV .. 2003

Severe Storms

Severe Thunderstorms Lightning, Heavy Rain & Hail

A thunderstorm develops in an unstable atmosphere when warm moist air near the earth’s surface rises quickly and cools. The moisture condenses to form rain droplets and dark thunder clouds called cumulonimbus clouds. These storms are often accompanied by hail, lightning, high winds, heavy rain and tornadoes. Thunderstorms are usually over in an hour, although a series of thunderstorms can last for several hours.

Lightning

The air is charged with electricity during a thunderstorm.   The most striking sign of this is lightning. Bolts of lightning hit the ground at about 40,000 kilometres per second - so fast that the lightning appears to be a single main bolt with a few forks when actually the opposite is true. The main bolt is a whole series of lightning strikes all taking the same path but at such a pace that the eye cannot distinguish between them. To estimate how far away the lightning is, count the seconds between the flash of lightning and the thunderclap. Each second is about 300 metres. If you count fewer than 30 seconds, look around for shelter; if fewer than five seconds, take shelter urgently. Lightning is near and you do not want to be the tallest object in the area. It is recommended to wait 30 minutes after the last lightning stroke in a severe storm before venturing outside again.

What To Do During A Severe Lightning Storm

What to do if you are in a building.

Stay inside. Stay away from windows, doors, fireplaces, radiators, stoves, metal pipes, sinks or other elecrical charge conductors. Unplug TVs, radios, toasters and other electrical appliances. Do not use the phone or other electrical equipment. ( You can use a cellular telephone. ) Do not go out to rescue the laundry on the clothesline as it conducts electricity.

What to do if you are outside.

Seek shelter in a building, cave or depressed area. If you are caught in the open, kneel with your feet close together and your head down ( the leap-frog position ). Do not lie flat - by minimizing your contact with the ground you reduce the risk of being electrocuted by a ground charge. Keep away from telephone and power lines, fences, trees and hilltops. Do not ride bicycles, motorcycles, tractors or golf carts or use metal shovels or golf clubs as they conduct electricity. If swimming or in a boat, get back to shore immediately.

What to do if you are in a car.

Stop the car and stay in it. Do not stop near trees or power lines that could fall.

Heavy Rain

A heavy rain fall can result in flooding. This is particularly true when the ground is still frozen or already saturated from previous storms. Floods may also result if a heavy rain coincides with the spring thaw. If you know there is flooding or the possibility of flooding in your area, keep your radio on to find out what areas are flooded, what areas are likely to be flooded as well as what roads are safe, where to go and what to do if the local emergency team asks you to leave your home. Generally speaking, it is a good idea to avoid driving through flooded roads and underpasses. The water may be a great deal deeper than it looks and you could get stuck. You may also want to avoid crossing bridges if the water is high and flowing quickly.

Hail

Hail forms when updrafts in thunderclouds carry raindrops upwards into extremely cold areas of the atmosphere. The raindrops freeze and are bounced around in the powerful winds within thunderclouds while new layers of ice are added.   Eventually, the hailstones grow too heavy to be supported by the updrafts and fall to the ground. Some hailstones are the size of peas while others can be as big as grapefruits.   Take cover when hail begins to fall.   Do not go out to cover plants, cars or garden furniture or to rescue animals.   Hail comes down at great speed, especially when accompanied by high winds. Although no-one in Canada has ever been killed by hail, people have been seriously injured by it.