Air & Pressure
Air Mass
A large body of air with relatively similar temperature and moisture characteristics throughout.
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A7 terms
Air & Pressure
Air Pressure
The force exerted by the weight of the atmosphere on a particular area.
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Instruments
Anemometer
An instrument used to measure wind speed.
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Air & Pressure
Atmosphere
The layer of gases surrounding Earth. Most of Earth's weather occurs in the troposphere, the lowest major layer of the atmosphere.
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Air & Pressure
Atmospheric Pressure
Another term for air pressure.
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Tropical & Flooding
Atmospheric River
A long, narrow region of concentrated moisture in the atmosphere that can transport large amounts of water vapor and produce heavy precipitation when it reaches land.
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Air & Pressure
Atmospheric Instability
A condition in which air can rise readily when disturbed. Strong instability can help thunderstorms develop.
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B3 terms
Instruments
Barometer
An instrument used to measure atmospheric pressure.
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Climate & Forecasting
Blocking Pattern
A persistent atmospheric circulation pattern that can slow or divert the usual movement of weather systems, sometimes causing weather conditions to remain in one area for an extended period.
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Winter Weather
Blizzard
A severe winter storm characterized by strong winds and greatly reduced visibility caused by falling or blowing snow for a prolonged period.
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C8 terms
Climate & Forecasting
Climate
The long-term pattern of weather conditions in a particular location or region, typically studied over many years or longer.
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Clouds & Moisture
Cloud
A visible collection of tiny water droplets, ice crystals, or both suspended in the atmosphere.
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Clouds & Moisture
Cloud Cover
The portion of the sky covered by clouds at a particular time.
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Fronts
Cold Front
The boundary where a colder air mass advances and replaces a warmer air mass.
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Clouds & Moisture
Condensation
The process in which water vapor changes into liquid water.
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Air & Pressure
Convection
The transfer of heat through the movement of a fluid such as air or water. In the atmosphere, warm air rising and cooler air sinking are examples of convection.
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Clouds & Moisture
Cumulonimbus Cloud
A large, vertically developed cloud associated with thunderstorms. These clouds can produce heavy rain, lightning, hail, strong winds, and tornadoes.
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Clouds & Moisture
Cumulus Cloud
A puffy cloud with a generally rounded appearance and a relatively flat base. Small cumulus clouds are often associated with fair weather.
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D4 terms
Clouds & Moisture
Dew
Water droplets that form when a surface cools enough for water vapor near the surface to condense.
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Clouds & Moisture
Dew Point
The temperature to which air must cool for it to become saturated with water vapor and condensation to begin.
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Storms & Tornadoes
Downburst
A powerful column of sinking air from a thunderstorm that spreads outward after reaching the ground.
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Air & Pressure
Downdraft
A current of air moving downward through the atmosphere.
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E2 terms
Climate & Forecasting
El Niño
A periodic climate pattern involving unusually warm ocean surface temperatures in the central and eastern tropical Pacific Ocean. It can influence weather patterns around the world.
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Clouds & Moisture
Evaporation
The process in which liquid water changes into water vapor.
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F5 terms
Tropical & Flooding
Flash Flood
A rapid and dangerous rise of water that can occur after intense rainfall, dam or levee failure, or other sudden events.
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Tropical & Flooding
Flood
An overflow of water onto land that is normally dry.
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Clouds & Moisture
Fog
A cloud that forms at or very close to Earth's surface.
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Climate & Forecasting
Forecast
A prediction of future weather conditions based on observations, measurements, computer models, and meteorological analysis.
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Fronts
Front
A boundary between two air masses with different characteristics, especially temperature and moisture.
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G1 term
Air & Pressure
Gust
A brief increase in wind speed that occurs over a relatively short period of time.
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H5 terms
Storms & Tornadoes
Hail
Balls or irregular pieces of ice that form inside strong thunderstorms and fall to the ground.
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Climate & Forecasting
Heat Index
A measure of how hot it feels to the human body when air temperature and humidity are considered together.
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Air & Pressure
High-Pressure System
An area where atmospheric pressure is relatively high compared with surrounding areas. High-pressure systems are often associated with sinking air and generally calmer weather.
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Clouds & Moisture
Humidity
The amount of water vapor present in the air.
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Tropical & Flooding
Hurricane
A tropical cyclone with maximum sustained winds of at least 74 mph (119 km/h) in the North Atlantic, central North Pacific, or eastern North Pacific.
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I2 terms
Winter Weather
Ice Storm
A winter storm in which freezing rain creates a significant layer of ice on surfaces.
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Air & Pressure
Instability
See .
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J1 term
Climate & Forecasting
Jet Stream
A relatively narrow band of strong winds high in the atmosphere. Jet streams generally flow from west to east and can strongly influence weather patterns.
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L4 terms
Climate & Forecasting
La Niña
A periodic climate pattern involving unusually cool ocean surface temperatures in the central and eastern tropical Pacific Ocean. It can influence weather patterns around the world.
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Winter Weather
Lake-Effect Snow
Snow produced when cold air moves across a relatively warmer lake, picking up heat and moisture before producing snow downwind of the lake.
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Storms & Tornadoes
Lightning
A powerful electrical discharge that occurs within a thunderstorm, between parts of a cloud, between clouds, or between a cloud and the ground.
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Air & Pressure
Low-Pressure System
An area where atmospheric pressure is relatively low compared with surrounding areas. Low-pressure systems are often associated with rising air, clouds, precipitation, and unsettled weather.
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M6 terms
Storms & Tornadoes
Mesocyclone
A large-scale rotating column of air within a severe thunderstorm. Mesocyclones are commonly associated with supercells and can sometimes contribute to tornado development.
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Climate & Forecasting
Meteorologist
A scientist who studies the atmosphere, weather, and atmospheric processes.
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Climate & Forecasting
Meteorology
The scientific study of Earth's atmosphere, weather, and atmospheric processes.
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Storms & Tornadoes
Microburst
A small but intense downdraft from a thunderstorm that produces powerful winds spreading outward after reaching the ground.
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Clouds & Moisture
Moisture
Water present in the atmosphere, including water vapor, liquid droplets, and ice.
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Tropical & Flooding
Monsoon
A seasonal change in prevailing winds that can produce major changes in precipitation patterns. Monsoons are especially important in parts of Asia, Africa, Australia, and other regions.
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N1 term
Climate & Forecasting
Nocturnal
Occurring or developing during nighttime. In meteorology, the term is often used to describe weather processes or storms that occur primarily at night.
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O1 term
Fronts
Occluded Front
A front that forms when a cold front catches up with a warm front, lifting the warm air away from the surface.
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P3 terms
Winter Weather
Polar Vortex
A large region of cold, low-pressure air that normally circulates around the polar regions in the upper atmosphere. Changes in its behavior can sometimes influence winter weather patterns farther south.
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Clouds & Moisture
Precipitation
Water that falls from the atmosphere to Earth's surface. Precipitation includes rain, snow, sleet, and hail.
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Air & Pressure
Pressure
The force exerted by the atmosphere over a particular area.
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Q1 term
Fronts
Quasi-Stationary Front
A boundary between air masses that moves very little. It can remain over an area for an extended period and produce prolonged clouds or precipitation.
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R3 terms
Clouds & Moisture
Rain
Liquid precipitation that falls from clouds to Earth's surface.
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Clouds & Moisture
Relative Humidity
The percentage of water vapor currently in the air compared with the maximum amount of water vapor the air could hold at that temperature.
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Winter Weather
Rime
Ice that forms when supercooled water droplets freeze onto exposed surfaces.
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S9 terms
Clouds & Moisture
Saturation
The condition in which air contains as much water vapor as it can hold at a particular temperature and pressure.
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Storms & Tornadoes
Severe Thunderstorm
A thunderstorm capable of producing particularly dangerous weather. In the United States, severe thunderstorm warnings are generally associated with damaging winds, large hail, or other significant hazards.
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Winter Weather
Sleet
Small pieces of ice that form when raindrops or melted snow refreeze before reaching the ground.
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Winter Weather
Snow
Solid precipitation made of ice crystals that form in clouds and fall to the ground.
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Winter Weather
Snow Squall
A brief but intense burst of heavy snow accompanied by strong, gusty winds and rapidly reduced visibility.
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Storms & Tornadoes
Storm Cell
An individual area of thunderstorm activity containing its own circulation and updraft and downdraft regions.
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Tropical & Flooding
Storm Surge
An abnormal rise in seawater above the predicted astronomical tide, caused primarily by a storm's winds pushing water toward the coast.
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Clouds & Moisture
Stratus Cloud
A low, widespread layer of cloud that often produces overcast skies and can bring light precipitation.
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Storms & Tornadoes
Supercell
A powerful thunderstorm containing a long-lasting rotating updraft called a mesocyclone. Supercells can produce tornadoes, large hail, damaging winds, and heavy rain.
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T10 terms
Climate & Forecasting
Temperature
A measurement of how hot or cold something is. In weather, air temperature is commonly measured in degrees Fahrenheit or Celsius.
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Instruments
Thermometer
An instrument used to measure temperature.
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Storms & Tornadoes
Thunder
The sound produced when air rapidly expands and contracts after being heated by a lightning discharge.
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Storms & Tornadoes
Thunderstorm
A storm that produces lightning and thunder. Thunderstorms may also produce heavy rain, strong winds, hail, and tornadoes.
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Storms & Tornadoes
Tornado
A violently rotating column of air extending from a thunderstorm toward the ground.
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Tropical & Flooding
Tropical Cyclone
A rotating low-pressure weather system that develops over warm tropical or subtropical waters. Depending on its location and strength, it may be called a tropical depression, tropical storm, hurricane, or typhoon.
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Tropical & Flooding
Tropical Depression
A tropical cyclone with maximum sustained winds of less than 39 mph (63 km/h).
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Tropical & Flooding
Tropical Storm
A tropical cyclone with maximum sustained winds of 39 to 73 mph (63 to 118 km/h).
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Air & Pressure
Trough
An elongated area of relatively low atmospheric pressure. Troughs are often associated with rising air, clouds, precipitation, and unsettled weather.
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Tropical & Flooding
Typhoon
A tropical cyclone with maximum sustained winds of at least 74 mph (119 km/h) occurring in the western North Pacific Ocean. It is the same type of storm known as a hurricane in some other parts of the world.
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U1 term
Air & Pressure
Updraft
A current of air moving upward through the atmosphere. Strong updrafts are an important part of thunderstorm development.
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V1 term
Clouds & Moisture
Virga
Precipitation that falls from a cloud but evaporates or sublimates before reaching the ground.
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W8 terms
Fronts
Warm Front
The boundary where a warmer air mass advances and replaces a colder air mass.
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Clouds & Moisture
Water Cycle
The continuous movement of water between Earth's surface, atmosphere, and other parts of the environment through processes such as evaporation, condensation, precipitation, and collection.
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Storms & Tornadoes
Waterspout
A rotating column of air that forms over a body of water and is connected to a cloud. Some waterspouts are tornadoes that occur over water, while others form through different processes.
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Climate & Forecasting
Weather
The condition of the atmosphere at a particular place and time, including temperature, precipitation, wind, humidity, clouds, and air pressure.
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Instruments
Weather Radar
A radar system used to detect precipitation and determine its location, movement, and intensity.
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Air & Pressure
Wind
The movement of air, generally from areas of higher pressure toward areas of lower pressure.
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Winter Weather
Wind Chill
A measure of how cold the air feels on exposed skin when the effects of wind and air temperature are combined.
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Air & Pressure
Wind Shear
A change in wind speed, wind direction, or both over a relatively short distance or change in altitude. Strong wind shear can influence thunderstorm development and tornado potential.
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Z1 term
Air & Pressure
Zone of Convergence
An area where winds from different directions meet. Converging air is often forced upward, which can contribute to cloud formation and precipitation.
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