THUNDERSTORMS
- 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.
TRUE!
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.
FALSE!
Lightning will always strike the tallest object around. The CN Tower is struck multiple times during a thunderstorm.
TORNADOES
- 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
- 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
- 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
- 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.