1. Weather Extreme Weather

2. Summary  Thunderstorms  Tornadoes  Floods  Droughts  Hurricanes, Typhoons & Tropical Cyclones  Blizzards

4. Thunderstorms  Has lightning, thunder, heavy rain and sometimes hail  Need two conditions:  Moisture to form clouds and precipitation  Strong lifting of air to make clouds that reach high in the atmosphere.

6. Thunderstorms Cont’d  Low temperature at high altitude creates a large temperature difference with the warm air that is lower.  The warm air rises quickly because of this temperature difference.  Water vapour rises and hits the cold air where it condenses making clouds.  Once the clouds are heavy enough rain falls in the downdrafts.

9. Thunderstorms cont’d  Thunderstorm clouds can reach higher than airplanes travel so pilots must maneuver around them.  As the thunderstorm reaches its end the flow of air becomes mostly downward.

11. Tornadoes  Because of their extremely high winds tornadoes can cause more damage in a short time than any other storm on Earth.  Tornadoes are a severe component of a thunderstorm.  It is very difficult to predict their path or even exactly where they are going to occur.

12. Tornadoes cont’d  Fast rising air in a thunderstorm sometimes begins to spin forming a funnel of air and moisture.  Rising air is replaced by cooler air which increases rotation.  The funnel cloud produces a pressure difference that can pick objects up.  Wind speed can be as high as 500 km/h.

15. Floods  Excess of water when the land can’t soak up any more water.  Can’t happen in Antarctica. Why not?  Two types of floods:  Flash  Broadside

17. Flash Floods  Little or no warning.  Can happen in cities if the water can’t drain fast enough.  Happens more when mountain valleys or gorges can’t accommodate spring rain and melting snow.  Can also occur when a dam bursts or overflows

19. Broadside Floods  Can cover large areas of land for months.  Can be predicted days or weeks before.  Causes:  Rivers flood from mountain snow melting.  Winter of heavy snowfall followed by rainy spring.  More rain than normal so soil becomes saturated.  Tropical storms bring lots of rain.

21. Droughts  No precipitation for a long time.  Can cause wildfires.  Can last for long periods of time.  Sometimes places flood from lots of rain at one time and then have a drought later.

23. Hurricanes, Typhoons and Tropical Cyclones  Same type of storm just located in different places of the world.  Has to be near the equator where the water surface temperature is high enough (about 27ºC)  Happen when cyclones become large enough.  If wind speed is 63km/h its called a tropical storm; if wind speed is 119km/h its called a hurricane.  Typhoons and tropical cyclones can be worse than hurricanes.

25.  Hurricane: western Atlantic Ocean, Caribbean Sea, Gulf of Mexico or eastern Pacific Ocean  Typhoon: northwestern Pacific Ocean or China Sea  Tropical Cyclone: Australia area or Indian Ocean

26. Hurricane Development  Warm air above warm water rises quickly carrying moisture with it.  As this air reaches higher altitude the water vapour condenses releasing heat and increasing speed of rising air.  Rising air creates a low pressure area that cool dry air moves into.  Cool air at the top also swirls outward and back down to be warmed again.

28. Hurricanes cont’d  The core of the hurricane is called the eye.  The eye is the low pressure area that is calm with clear skies.  Hurricanes can carry lots of rainfall inland creating floods and destruction.

31. Blizzards  Severe snow storm with strong winds and low temperatures.  Winds must exceed 55km/h and visibility must be less than 0.5km.  Blizzards develop similarly to thunderstorms but with snow because of the cold temperatures.  What are some dangers of blizzards?