National Weather Service, Lubbock Texas
Glossary of Some Commonly Used Weather Terms

  • Anemometer:  An instrument for measuring the force or the speed of the wind.

  • Anticyclone:  The clockwise wind flow around an area of high pressure.

  • Atmosphere:  The gaseous envelope surrounding any heavenly body.

  • Barometer:  An instrument used for measuring atmospheric pressure.

  • Blizzard:  Wind of at least 35 MPH along with considerable falling and / or blowing snow reducing visibilities to less than 1/4 mile for a period of at least three hours.

  • Cap:  A warmer layer of air above the surface which suppresses convection (thunderstorms). May be referred to as a capping inversion or lid.

  • Ceiling:  The height above the surface of a cloud deck.

  • Climate:  The weather conditions which, in  combination, characterize a region or place.

  • Climatology:  The science and study of climate, the aggregates of all weather conditions at a point over a long period of time.

  • Clouds:
    1. Cirrus:  A form of high cloud composed of ice crystals.
    2. Cumulus cloud:  A round fluffy cloud which forms in the lower levels of the atmosphere.  These clouds are often produced by convection.  If the air mass is unstable these cumulus clouds will grow vertically into cumulus congestus or cumulonimbus (thunderstorm).
    3. Stratus:  A continuous horizontal layer of cloud.
    4. Nimbus:  A cloud form in which rain falls.
    5. Scud:  Low clouds which form within the outflow of a thunderstorm.
  • Condensation:  The process in which water vapor becomes liquid.

  • Convection:  The transfer of heat ( and other properties) by movement of air; typically in the vertical by the overturning within an unstable air mass, resulting in the development of cumulus clouds.

  • Cyclone:  The counterclockwise wind flow around a center of low pressure.

  • Dewpoint:  The temperature at which air must be cooled in order for moisture in the atmosphere to condense.  The higher the moisture content in air the higher it's dewpoint. 

  • Drought:  An extended period with little or no precipitation.

  • Dryline:  A surface boundary which demarks a tight gradient in surface moisture.

  • Dust Devil:  A small but rapidly rotating column of air which is typically 1 to 50 feet wide, and of short duration that is made visible by dust, sand and small debris picked up from the ground.  Dust Devils usually develop on warm and sunny afternoons.

  • Front:  A boundary between two air masses of different temperature.

  • Funnel Cloud:  A rotating column of air which usually extends down from a a cumulonimbus cloud ( thunderstorm) that does not reach the ground.

  • El-Nino:  A large scale weather pattern which occurs when the ocean waters over the eastern pacific warm above normal readings..  This pattern causes the subtropical jet stream, which is normally located over the southern United States, to intensify.  The intense subtropical jet stream brings more upper level systems across the southern United States, causing rainfall to increase.

  • Evaporation:  The physical process in which a  liquid changes into a gas. 

  • Gust Front:  A cold surge of air produced by a thunderstorm downdraft. The more intense the thunderstorm downdraft the greater the wind surface wind behind the gust front.

  • Gustnado:  A circulation which develops vertically from the ground up along an outflow boundary or gust front produced from a thunderstorm.  Unlike a tornado the gustnado is not attached to the thunderstorm and is usually weaker than most tornadoes.

  • Hail:  Pieces of ice which form and grow through the process of riming in the super-cooled water found within a cumulonimbus cloud while suspended within in the updraft of a thunderstorm.  When the the hail grows and the weight of the hail exceeds the force of rising air within the thunderstorm, the hail will fall to the ground.  Usually the more intense a storms updraft the larger the hail.

  • Hydrometeor:  Any form of precipitation.
    1. Rain:  Liquid precipitation in the form of a drop, forms when atmospheric moisture condenses on a particulate (usually within a cloud) and grows in mass to where the force of gravity brings it to the surface.
    2. Snow:  Frozen precipitation in the form of crystalline shapes, forms when ice crystals conglomerate in clouds which are below freezing, as the snow flake grows in mass  the force of gravity will then bring the snow flake to the surface.
    3. Sleet:  Forms in the same process of rain within the cloud but falls through a sub freezing column of air which causes the liquid drop to freeze into a solid.
    4. Graupel:  Snow flakes that become rounded pellets due to riming.  Groupel is sometimes mistaken as sleet or hail.
    5. Freezing Rain:  Rain which falls to the surface and freezes on contact.  This usually occurs when a shallow cold air mass, which may be only be several feet deep, is in place.
    6. Drizzle:  Liquid drop sizes which are much smaller than rain drops that reach the surface.
  • Jet Stream:  Relatively strong winds which are concentrated in a narrow band in the atmosphere.  Jet Streams are usually 1000s of miles long and 100's of miles wide but are only a few 1000 feet thick.

  • La-Nina:  A large scale weather pattern which occurs when the ocean waters over the eastern pacific cool below normal readings. This pattern usually causes the subtropical jet stream to weaken or migrate north over the northern US and Canada.  This weather pattern brings dry and warm conditions to most of the United States.

  • Mesocyclone:  A cyclonic (counter clockwise) or anti-cyclonic (clockwise) rotating column of air found within a thunderstorm updraft.  This rotating column of air may be located at either the mid-levels or low-levels, or at both the mid and low-levels simultaneously within a thunderstorm.

  • Meteorology:  Study of the state and processes of the atmosphere

  • Occluded front:  A complex front which forms when a cold front over takes a warm front.

  • Precipitation:  The accumulated depth of rain or drizzle, and also melted water containing snow and other frozen precipitation including hail.

  • Psychrometer:  An instrument for measuring the moisture content of the air by use of a dry- and wet-bulb thermometer.

  • Relative Humidity:  The ratio of water vapor contained in air compared to the maximum amount of moisture that air can hold at a given temperature and pressure.

  • Ridge:  An elongated area of high pressure.

  • Rime:  A deposit of ice from when supercooled water droplets freeze on contact with an object.

  • Squall line:  A solid line of thunderstorms which form ahead or along a surface boundary, such as a front, dryline, or outflow boundary.

  • Stratosphere:  The second lowest of the main layers of the atmosphere; it is characterized by more or less isothermal conditions ( temperature is constant with height) and a highly stable stratification.

  • Stratus:  A continuous horizontal layer of cloud.

  • Sublimation:  The process in which ice changes directly to water vapor without melting.

  • Supercell Thunderstorm:  A thunderstorm which exhibits mid-level rotation (  i.e. a mid-level mesocyclone) and a steady state updraft.  These thunderstorms are usually severe, producing any of the following:  large hail, high winds and tornadoes.

  • Thunder:  A sound wave produced when lightning super heats a volume of air. The super heated air rapidly expands producing a sound wave which travels through the atmosphere.

  • Thunderstorm:  Cumulonimbus cloud from which thunder is heard.

  • Tornado:  A violently rotating column of air which makes contact with the ground.  Tornadoes are usually spawned by the low-level mesocyclone of a supercell thunderstorm.

  • Trough:  An elongated area of low pressure.

  • Updraft:  The area of a thunderstorm where the maximum vertical motion is occurring.

  • Upper Low:  A low pressure center located in the mid and upper levels of the atmosphere which moves from west to east within the jet stream.  These disturbances are also called upper level troughs or short-wave troughs.

  • Virga:  Precipitation that falls from clouds but evaporates in dry air beneath the cloud before reaching the ground.

  • Vertical Wind Shear:  The turning of wind direction and/or the increase of wind speed with height.  A clock wise turning with height along with an increase of wind speed with height is a key ingredient for the development of supercell thunderstorms given a high degree of atmospheric instability.

  • Wall Cloud:  A lowered cloud base under a thunderstorm.  Wall clouds that rotate around a vertical axis are called low-level mesocyclones and may be precursors to funnel clouds and potential tornadoes.

  • Wind:  The movement of air (both direction and speed) which is caused mainly by horizontal pressure differences.  Wind direction is measured from which it's blowing.


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