– Thunderstorms are the most common type of storm.
– These bring heavy rain, thunder, lightning, hail, and the odd tornado.
– Two conditions must exist for a thunderstorm to form:
Moisture is needed to form clouds and rain.
Warm air must be pushed up in the atmosphere to form large cumulus clouds
– As warm, moist air rises, a large cumulus cloud is created. This cloud warms the air around it therefore allowing it to rise even higher.
– During a thunderstorm, lightning and thunder are produced.
– Lightning is produced when electricity travels between negatively and positively changed parts of a cloud.
– This electricity discharges from the cloud and lightning flashes (which can create temperatures up to 27,760oC).
– When lightning occurs, air expands and contracts rapidly creating a loud noise called thunder.
– If lightning and thunder occur at the same time, why do we not hear and see the two events at the same time? This is because light travels a lot faster than sound. Therefore, when there is a large gap of time between lightning and thunder, the thunderstorm is further away.
– TRUE OR FALSE?
Never take shelter under a tree during a thunderstorm.
Lightning will ALWAYS strike the tallest object around so that it can take the shortest path possible to the ground. If you are outside during a thunderstorm, stay low and stay away from any tall object.
Lightning never strikes the same place twice.
Lightning will always strike the tallest object around. The CN Tower is struck multiple times during a thunderstorm.
– Tornadoes form when fast-rising air (which occurs in a thunderstorm) begins to spin, forming a funnel of warm air and speeds.
– As the air rises and cools, the spinning speeds up.
– The funnel eventually forms an extremely low pressure area where it touches the ground.
– The low pressure area acts like a vacuum therefore sucking up all the material around it.
– Wind speeds in the tornado can be as high as 500 km/h.
– Hurricanes are common in the late summer or early fall over warm waters just north of the equator.
– Air is warmed from the ocean and an updraft is created. The air pressure in the center of the updraft is low therefore producing a swirling, circling, counterclockwise movement.
– More warm air is continuously pulled into the centre of the storm therefore adding more energy to the storm.
– Once the winds of the storm rise above 119km/h, the tropical storm becomes classified as a hurricane.
– The center of a hurricane is called the eye. The eye of a hurricane is calm and clear.
– Hurricane winds are usually not as fast as tornado winds, however, hurricanes can last for a couple of weeks and therefore create more damage.
– Blizzards are severe snowstorms with strong winds and low temperatures.
– Blizzards occur when winds are at a speed of 55km/h, temperatures are very low, and visibility is less than 200m.
– Blizzards develop the same way as thunderstorms except the low temperatures bring snow instead of lightning.
– Due to the lake-effect (remember section 4.5 – Regional Weather?) the area around the Great Lakes experiences a lot of blizzards.
– Floods can occur anywhere in the world except Antarctica.
– Floods are an excess of water that cannot be absorbed quickly enough by the ground.
– There are two types of floods: flash floods and broadside floods.
– Flash Floods
These occur with little or no warning usually in cities where water cannot be drained away quickly enough by storm sewers.
– Broadside Floods
These cover large areas of land and can last for months.
These floods can usually be predicted in advance.
These floods may occur if a winter with heavy snowfall is followed by heavy rainfall in the spring. This can cause rivers to overflow and flood surrounding areas.
These floods can also be caused by tropical storms.