Weather I. The air around us A. atmosphere is a layer of gases that wrap around the Earth like a blanket. II. Weather Temperature Humidity Air pressure Wind 1. contains the air we breathe, protects us from the sun s harmful radiation, and helps the planet recycle its water supply 2. made up mostly of nitrogen (78%) and oxygen (21%) 3. also made up of tiny particles of soil, pollen grains, and soot from fires 4. carbon dioxide and water vapor are green house gases carbon dioxide absorbs Earth s heat to keep the planet warm and water vapor helps form clouds that are part of the water cycle A. We can observe and describe the weather by measuring properties of air. 1. temperature 2. humidity 3. air pressure 4. wind B. We can also use these properties to predict weather in the future Property Definition Drawing
C. Properties 1. temperature is how hot or cold something is 2. humidity is the amount of water vapor air can hold a. air that is humid holds a lot of water vapor b. air often feels wetter in summer because warm air holds more water vapor than cold air c. humid air is more likely to produce clouds and precipitation d. dry air is more likely to be associated with fair weather 3. air pressure is the force of the weight of air pressing down on Earth a. air has weight, so the more air there is above you, the more air pressure there is b. air pressure is not always the same sometimes it can be low and sometimes it can be high 1. Lows temperature affects air pressure. When air gets warmer, gas particles spread apart, and the air gets lighter and rises. Rising air presses down with less force, so that is an area of low air pressure 2. Highs when air gets cooler, the particles get closer together, so the air is heavier and it sinks. This is an area of high pressure. Clouds can t form when air is sinking, so with a high pressure system, the weather is usually clear. On the other hand, when a low forms, clouds tend to form and there will often be rain 4. wind is the movement of air from areas of high pressure to areas of low pressure
a. when the difference in air pressure is great, wind blows faster, when the difference is small, the wind blows slower III. Observing weather patterns A. Scientists use weather instruments to collect weather data and predict weather 1. Thermometer measures the temperature in degrees 2. Anemometer measures wind speeds 3. Wind vane measures the direction the wind is blowing a change in wind direction can mean a change in weather 4. Hygrometer measures the humidity in the air 5. Barometer measures air pressure 6. Rain gauge measures the amount of rainfall B. Scientists also use other weather tools 1. Satellites to study the movement of storms 2. Weather balloons are used to collect data on temperature, air pressure, and humidity 3. radar looks inside clouds IV. Air masses A. air moves as huge masses 1. several miles thick and 1,000 miles across 2. temperature and humidity is about the same throughout an air mass 3. a neighboring air mass may have a different temperature, humidity, and weather
4. every mass takes on the properties of the area where it is formed 5. cold air masses are formed in cold air regions warm air masses are formed in warm regions 6. some masses are formed over land and some over water 7. when they move, they affect the weather of places they pass over 8. masses that form over land are usually dry over water they are usually humid V. Fronts A. where two air masses meet 1. the edge of a moving mass of cooler air is a cold front 2. the edge of a moving mass of warm air is a warm front A warm front: a. brings warmer temperatures b. fast moving warm air mass meets a cold air mass 1. the lighter warm air mass rides up over the heavier cold air 2. as the warm air rises, and cools, the water vapor condenses to form clouds 3. the sky fills with thicker lower clouds and there can be light rain that lasts for hours or days A cold front: 1. brings cooler temperatures 2. forms where a faster moving cold air mass meets a warm air mass
3. the faster, heavier cold air plows under the warm air and it pushes the warm air up sharply 4. water vapor condenses to form clouds 5. these bring severe weather, including tormadoes VI. Climate A. Climate is the general weather of an area over a long period of time 1. some places have warmer climates than others and some places have cooler climates 2. The range of temperatures and the amount of precipitation a place experiences determines its climate 3. Each type of climate has certain weather patterns that are the same or repeated year after year 4. The climate of a region also affects the environment found there a. deserts are very dry, but can be either hot or cold b. swamps are usually found in warm and wet environments c. mountains have different climates 1. tops of mountains have cool temps and low humidity 2. the base of a mountain will usually have the same climate as the surrounding area B. Factors affecting climate 1. Average temperatures and precipitation are the key parts a. latitude, elevation, and nearness to large bodies of water 1. latitude is the distance north or south of the equator, which affects temperature
2. elevation is how above sea level an area is a. air gets cooler as it rises, so higher elevation usually means lower temperatures 3. large bodies of water temperatures are usually milder near oceans and large lakes because water heats and cools at a slower rate than land VII. Severe weather A. Hurricanes 1. Earth s biggest storms hundreds of kilometers wide with winds that can top 155 mph 2. Warm ocean water and high humidity feeds the storm a. Hurricane watch the storm is still a couple of days away (it can hit the area or change paths) b. Hurricane warning the storm will hit every family should have an emergency plan: 1. a place where everyone meets in an emergency 2. names and phone numbers of people to contact 3. addresses and phone numbers of people to contact 4. name and phone number of family doctor or hospital 5. name and date of birth of each family member 6. any special needs of family members, such as medications or allergies 7. plan for any pets in your family
B. Tornadoes 1. Tornadoes are among the most destructive storms 2. Winds can be up to 250mph 3. Often form at fronts, where very cold air masses meet very warm air masses a. tornado watch conditions are right for a tornado to form b. tornado warning a tornado has been spotted 1. take cover right away lowest part of the house in an inside room with no windows C. Winter storms 1. In northern areas 2. These storms can bury roads and buildings and create icy and snowy conditions that are dangerous for people 3. Can last for days a. keep an emergency supply kit in the car and in the house to be prepared for several days without power or heat D. Floods 1. Floods happen when there is more precipitation than usual in a region ground cannot absorb the water and it runs into rivers and streams 2. They can also happen when there is a prolonged period of rain and the ground is saturated and cannot absorb any more water a. have an emergency plan b. have an emergency supply kit