| Term | Definition |
|---|
| air mass | A huge body of air that has similar temperature, pressure, and humidity throughout. |
| tropical air mass | A warm air mass that forms in the tropics and has low air pressure |
| polar air mass | A cold air mass that forms north of 50 degree north latitude or south of 50 degree south latitude and has high air pressure. |
| continental air mass | A dry air mass that forms over land. |
| maritime air mass | A humid air mass that forms over oceans. |
| front | The area where air masses meet and do not mix. |
| cold front | When a rapidly moving cold air mass runs into a slowly moving warm air mass, the denser cold air slides under the lighter warm air. The warm air is pushed upward. Depending on how much water vapor is present will determine whether precipitation occurs. |
| warm front | A moving warm air mass collides with a slowly moving cold air mass. The warm air mass moves over the cold air mass due to density. Precipitation may occur for an extended period of time if the warm air mass contains a lot of water vapor. |
| stationary front | Occurs when a warm and cold air mass meet and neither has enough energy to move the other so a 'stand off'' occurs. It can bring several days of clouds and precipitation. |
| occluded front | A warm air mass is caught between 2 cooler air masses lift the warmer air mass off of the ground. The temperature near the ground is cooler. Precipitation can occur as the warm air mass cools and water vapor condenses. |
| cyclone | A swirling center of low air pressure. |
| anticyclone | A high-pressure center of dry air. |
| 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 cloud and the ground. |
| thunder | The rapidly heated air from the lightning bolt expands suddenly and explosively causing the explosive sound 'thunder'. |
| 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 km/h or higher; typically about 600 km across. |
| eye of hurricane | The calm center part of the hurricane. |
| storm surge | A dome of water that sweeps across the coast where a hurrican lands. |
| evacuate | To move away temporarily. |
| lake-effect snow | In the Great Lakes region when a cold dry air mass moves over the lake it picks up heat and water vapor. As it reaches landfall again the air rises, cools, and snowfall occurs. |
| flash flood | A sudden, violent flood that occurs within a few hours, or even minutes, of a heavy rainstorm. |
| meteorologist | Scientists who study the causes of weather and try to predict it. |
| El Nino | An event that occurs every 2-7 years in the Pacific Ocean, during which winds shift and push warm surface 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. |
| isotherms | Lines on a map joining places that have the same temperature. |
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