Severe Weather & Climate Notes

Fronts〉When fronts move through

an area, the result is usually precipitation and a change in wind direction and temperature.

• air mass: a large body of air where temperature and moisture content are similar throughout

• front: the boundary between air masses of different densities and usually different temperatures

Fronts• Clouds, rain, and sometimes snow can occur at

fronts.

• Front types include • warm fronts• cold fronts• stationary fronts

Thunder & Lightning• Lightning is a discharge of

atmospheric electrical energy.

• Water droplets and ice crystals in thunderclouds build up electrical charges.

• Lightning is a big spark that jumps between clouds or between clouds and Earth to equalize the charge.

• Lightning heats the air so fast that the air expands faster than the speed of sound.

• The shockwave created is thunder.

Severe Weather• Tornadoes are funnels of

high-speed wind.

• Tornado winds are the most violent winds on Earth.• Wind speeds may reach up to

500 km/h.

• Tornadoes typically form along a front between cool, dry air and warm, humid air.

• funnel cloud: a column of water droplets

Severe Weather• Hurricanes are large,

rotating tropical storm systems.

• These storms are called

• hurricanes in North America and the Caribbean• cyclones in the Indian

Ocean• typhoons in the western

Pacific

• tropical depressions: intense low-pressure areas that can become hurricanes

Climate

〉Weather changes from day to day, but climate does not change as quickly.

• climate: the average weather conditions in an area over a long period of time. Two main factors are temperature and precipitation.

Climate

• Temperatures tend to be higher close to the equator.

• Sunlight strikes the earth more directly close to the equator.

• The sun’s rays are less concentrated at the poles, and do not warm the atmosphere as much.

Climate• Earth’s tilt and rotation

account for our seasons.• When the North Pole is

tilted toward the sun, the Northern Hemisphere experiences summer.

• There is more daylight, and the temperature increases.

• Earth is farthest from the sun on July 4.

• When the South Pole is tilted toward the sun, the Southern Hemisphere experiences summer.

Climate• Earth’s surface features

affect climate.

• topography: the size and shape of the land surface features of a region, including its relief• Variations in topography affect

the climate of a region.• Mountains can trap moisture on

one side.

• Deserts may form on the dry side of a mountain.

• Broad flat surfaces allow winds to merge on the plains.

• Thunderstorms and tornados may form.

Exit Slip• Determine whether each of the following

statements describes a warm front or cold front.• Warm air mass moves above slow cold air mass• Thunderstorms and high winds characterize this type of

front• Cold air moves quickly under slow air mass• Steady rain

• Grapes grow well in areas where climate is generally mild. Would you recommend planting grapes in California or North Dakota? Explain.

Climate Change• Global climate changes

over long periods of time.

• Many factors produce changes in Earth’s climate, such as:• eruptions of volcanoes • shift of the continents• changes in Earth’s tilt

• Scientists think that increases in human-made greenhouse gases have caused the recent increase in global average temperature.