1. Severe Weather
S6E4 b. Relate unequal heating of land and water surfaces to form large global wind systems and weather events such as tornados and thunderstorms.
S6E4c. Relate how moisture evaporating from the oceans affects the weather patterns and weather events such as hurricanes.

2. Weather vs. Climate
Weather is the condition of the atmosphere at a certain time and place
Weather reports may not always be right, but are specific
Climate is the average weather conditions of an area over a long period of time.
Usually described in terms of temperature and precipitation

3. Thunderstorms
Thunderstorm- a usually brief, heavy storm that consists of rain, strong winds, lightning, and thunder
They can occur along cold fronts, and in other places as well
Two atmospheric conditions are required for thunderstorm: warm moist air near Earth’s surface and an unstable atmosphere
Unstable atmosphere = surrounding air colder than the rising air mass.

4. Thunderstorms cont.
The atmosphere is unstable where cold air is above and around warm wet air. This instability allows the air masses to move, which leads to the formation of clouds
When lightning strikes, energy is released. This energy is transferred to the air and causes the air to expand rapidly and send out sound waves
Thunder is the sound that results from the rapid expansion of air along the lightning strike.

5. Tornadoes Happen in only 1% of all thunderstorms
Tornado is a destructive, rotating column of air that has very high wind speeds, is visible as a funnel-shaped cloud, and touches the ground
Produce most of Earth’s most powerful winds
Presence of dust and debris reason funnel cloud looks dark, causes most damage to buildings

6. Hurricanes
Hurricane is a large, rotating low-pressure system that forms over the warm waters of oceans near the equator
Happen summer or fall, when oceans have most heat energy
Form over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico
Similar storms are called cyclones or typhoons

7. Hurricanes
Hurricane starts as a low over warm waters of Atlantic, it gains energy from the warm humid air above the water
As is stays over the ocean, it continues to pick up energy which increases the speed of rotating air, increasing the wind speeds
When a wind speed reaches 120 km/hr the storm is called a hurricane
Due to global wind patterns, hurricanes often strike islands in Caribbean sea or the eastern coast of the U.S.
When hurricanes reach land, it weakens without the energy from the ocean. When wind speeds decrease, the hurricane is called a tropical storm or depression
Atlantic hurricane season is from Apr. to Nov.

8. Eye of a Hurricane A hurricane has a typical shape.
The eye of a hurricane is a place of very low pressure with no clouds above it.
In the eye, it is very calm and sunny.
The most violent winds in a hurricane form the wall of the hurricane’s eye.

9. Quick Check
A high speed, spinning cloud in shape of a funnel is _________________
What causes thunder_____________________
A thunderstorm is most likely to occur when the weather is
A. cool and dry
B. Hot and dry
C. Cool and humid
D. Hot and humid