Weather Patterns

Air Masses and Fronts - Vocabulary Air Mass – A huge body of air that has similar temperature, pressure, and humidity throughout. Tropical – A warm air mass that forms in the tropics and has low air pressure. Polar – A cold air mass that forms north of 50° north latitude or south of 50° south latitude and has high air pressure. Maritime – A humid air mass that forms over oceans. Continental – A dry air mass that forms over land.

Air Masses and Fronts - Vocabulary Front – The area where air masses meet and do not mix Occluded – Cut off, as the warm air mass at an occluded front is cut off from the ground by cooler air beneath it. Cyclone – A swirling center of low air pressure. Anticyclone –A high-pressure center of dry air.

Air Masses and Fronts – Main Ideas Four major types of air masses influence the weather in North America: maritime tropical, continental tropical, maritime polar, continental polar. When air masses collide, they form four types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts. Cyclones and decreasing air pressure are associated with storms and precipitation.

Air Masses and Fronts – Review Questions What two main characteristics are used to classify air masses? What is a front? Name and describe four types of fronts. What is a cyclone? What type of weather does it bring? Why do maritime polar air masses have more effect on the West Coast than the East Coast?

Storms - Vocabulary Storm – A violent disturbance in the atmosphere Lightning – A sudden spark, or energy discharge, caused when electrical charges jump between parts of a cloud or between a cloud and the ground. Tornado – A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth’s surface, usually leaving a destructive path. Hurricane – A tropical storm that has winds of 119 kilometers per hour or higher; typically about 600 kilometers across.

Storms - Vocabulary Storm surge – A dome of water that sweeps across the coast where a hurricane lands. Evacuate – To move away temporarily.

Storms – Main Ideas Thunderstorms and tornadoes form within large cumulonimbus clouds. During thunderstorms, avoid touching metal objects. A hurricane begins over warm water as a low-pressure area. If you hear a hurricane warning and are told to evacuate, leave the area immediately. Snow falls when humid air cools below 0°C. If you are caught in a snowstorm, try to find shelter from the wind.

Storms – Review Questions What weather conditions are most likely to cause thunderstorms and tornadoes? What is the most common path for the hurricanes that strike the United States? What safety precautions should you take if a tornado is predicted in your area? If a hurricane is predicted?

Floods - Vocabulary Flash flood – A sudden, violent flood that occurs within a few hours, or even minutes, of a heavy rainstorm.

Floods – Main Ideas Floods occur when so much water pours into a stream or river that it overflows its banks on either side of the channel. The first rule of flood safety: Move to higher ground and stay away from flood waters.

Floods – Review Questions How can precipitation cause flooding? What should you do to stay safe during a flood? What is the difference between a flood watch and a flood warning? Name three tools that supply information used in forecasting floods and providing flood information.

Predicting the Weather - Vocabulary Meteorologist – Scientist who study the causes of weather and try to predict it. El Niño – an event that occurs every two to seven years in the Pacific Ocean, during which winds sift and push warm water toward the coast of South America; it can cause dramatic climate changes. Isobar – Lines on a map joining places that have the same air pressure. Isotherm – Lines on a map joining places that have the same temperature.

Predicting the Weather – Main Ideas Meteorologists interpret weather information from local weather observers, instruments carried by balloons, satellites, and weather stations around the world. Changes in weather technology have occurred in two areas: gathering weather data and using computers to make forecasts. Standard symbols on weather maps show fronts, areas of high and low pressure, types of precipitation, and temperatures.

Predicting the Weather – Review Questions What kinds of technology do meteorologists use to help predict the weather? Name at least three types of information you could get from a weather map of your area. What lines on a weather map connect points that have the same temperature?