\', Stephenson County Emergency Management Agency, \' - \', , \' Clouds & Lightning
Create an Account or Login
Site Navigation
Storm Images
Shelf Cloud 6-19-14
Distracted Driving
Don't text and drive
Login
Nickname

Password


Don't have an account yet? You can create one. As a registered user you have some advantages like theme manager, comments configuration and post comments with your name.
Stephenson County Emergency Management Agency Frequently Asked Questions



Category: Main -> Weather Terms

Question
·  Accessory Clouds
·  Acid Rain
·  Advection
·  Advisory
·  Air Mass
·  Air Pressure
·  Altitude
·  Anemometer
·  Anvil Cloud
·  Atmosphere
·  Atmospheric Pressure
·  Back-building Thunderstorm
·  Ball lightning
·  Barometric pressure
·  Beaufort Scale
·  Beaver Tail
·  Black Ice
·  Blizzard
·  Bow echo
·  Cap (or Capping Inversion)
·  Ceiling
·  Cirrus Clouds
·  Climate
·  Cloud Base
·  Cold-air Funnel
·  Cumulonimbus Cloud
·  Cumulus Cloud
·  Debris Cloud
·  Depression
·  Derechoe
·  Dew point
·  Downburst
·  Downdraft
·  Drought
·  El Nino
·  Evaporation
·  Fahrenheit
·  Flood
·  Front
·  Fujita Scale
·  Funnel Cloud
·  Gustnado (or Gustinado)
·  Hail
·  High
·  Hook Echo
·  Hygrometer
·  Inflow Bands (or Feeder Bands)
·  Inflow Jets
·  Instability
·  Isobar
·  Jet Stream
·  Knot
·  La Nina
·  Leeward
·  Lightning
·  Low
·  Macroburst
·  Mamma Clouds
·  Mesocyclone
·  Microburst
·  Millibar
·  Multicell Cluster Thunderstorm
·  Multivortex Tornado
·  Outflow
·  Outflow Boundary
·  Precipitation
·  Prevailing Wind
·  Radar
·  Rain-Free Base
·  Rain Guage
·  Relative Humidity
·  Saturation
·  Scud Clouds
·  Severe Thunderstorm
·  Shelf Cloud
·  Squall
·  Squall Line
·  Straight Line Winds
·  Supercell Thunderstorm
·  Sustained Winds
·  Tail Cloud
·  Thunder
·  Thunderstorm
·  Tornado
·  Trough
·  Twister
·  Updraft
·  Vertical Shear
·  Virga
·  Vortex
·  Wall Cloud
·  Warning
·  Watch
·  Weather
·  Wedge (or Wedge Tornado)
·  Wind Chill
·  Wind Direction
·  Wind Shear
·  Wind Vane
·  Where can I find more weather terms?

Answer
·  Accessory Clouds

Clouds that are dependent on a larger cloud system for development and continuance.  Accessory clouds associated with the thunderstorm include roll, shelf, mammatus, and wall clouds.

[ Back to Top ]

·  Acid Rain

Cloud or rain droplets containing pollutants, such as oxides of sulfur and nitrogen, to make them acidic (e.g. pH < 5.6). 

[ Back to Top ]

·  Advection

The horizontal transport of air, moisture or other atmospheric properties.  Commonly used with temperatures, i.e., "warm air advection".

[ Back to Top ]

·  Advisory

Advisories are issued for weather situations that cause significant inconveniences but do not meet warning criteria and, if caution is not exercised, could lead to life-threatening situations.  Advisories are issued for significant events that are occurring, are imminent, or have a very high probability of occurrence. 

[ Back to Top ]

·  Air Mass

A large body of air that has similar horizontal temperature and moisture characteristics. 

[ Back to Top ]

·  Air Pressure

(atmospheric pressure) air  pressure is the force exerted on a surface by the weight of the air above it.  The internationally recognized unit for measuring this pressure is the kilopascal. 

[ Back to Top ]

·  Altitude

Height expressed as the distance above a reference point, which is normally sea level or ground level. 

[ Back to Top ]

·  Anemometer

An instrument that measures wind speed. 

[ Back to Top ]

·  Anvil Cloud

The flat, spreading top of a cumulonimbus cloud, often shaped like an anvil.  Thunderstorm anvils may spread hundreds of miles downwind from the thunderstorm itself, and sometimes may spread upwind. 

[ Back to Top ]

·  Atmosphere

The mass of air surrounding the earth and bound to it more or less permanently by the earth''s gravitational attraction. 

[ Back to Top ]

·  Atmospheric Pressure

(also called air pressure or barometric pressure) The pressure asserted by the mass of the column of air directly above any specific point. 

[ Back to Top ]

·  Back-building Thunderstorm

A thunderstorm in which new development takes place on the upwind side (usually the west or southwest side), such that the storm seems to remain stationary or propagate in a backward direction. 

[ Back to Top ]

·  Ball lightning

A relatively rarely seen form of lightning, generally consisting of an orange or reddish ball of the order of a few cm to 30 cm in diameter and of moderate luminosity, which may move up to 1 m/s horizontally with a lifetime of a second or two. 

[ Back to Top ]

·  Barometric pressure

The actual atmospheric pressure value indicated by a pressure sensor. 

[ Back to Top ]

·  Beaufort Scale

A scale that indicates the wind speed using the effect wind has on certain familiar objects. 

[ Back to Top ]

·  Beaver Tail

A particular type of inflow band with a relatively broad, flat appearance suggestive of a beaver''s tail.  It is attached to a supercell''s general updraft and is oriented roughly parallel to the pseudo-warm front, i.e., usually east to west or southeast to northwest.

[ Back to Top ]

·  Black Ice

thin, new ice that forms on fresh water or dew covered surfaces; it is common on roadways during the fall and early winter and appears "black" because of its transparency. 

[ Back to Top ]

·  Blizzard

Includes winter storm conditions of sustained winds or frequent gusts of 35 mph or more that cause major blowing and drifting of snow, reducing visibility to less than one-quarter mile for 3 or more hours.  Extremely cold temperatures often are associated with dangerous blizzard conditions.

[ Back to Top ]

·  Bow echo

A radar echo which is linear but bent outward in a bow shape.  Damaging straight-line winds often occur near the "crest" or center of a bow echo.  Areas of circulation also can develop at either end of a bow echo which sometimes can lead to tornado formation - especially in the left (usually northern) end, where the circulation exhibits cyclonic rotation.

[ Back to Top ]

·  Cap (or Capping Inversion)

A layer of relatively warm air aloft (usually several thousand feet above the ground) which suppresses or delays the development of thunderstorms.  Air parcels rising into this layer become cooler than the surrounding air, which inhibits their ability to rise further.  As such, the cap often prevents or delays thunderstorm development even in the presence of extreme instability. 

[ Back to Top ]

·  Ceiling

The height of the lowest layer of broken or overcast clouds. 

[ Back to Top ]

·  Cirrus Clouds

High clouds, usually above 18,000 feet, composed of ice crystals and appearing in the form of white, delicate filaments or white or mostly white patches or narrow bands. 

[ Back to Top ]

·  Climate

The prevalent long term weather conditions in a particular area.  Climatic elements include precipitation, temperature, humidity, sunshine and wind velocity and phenomena such as fog, frost, and hail storms.  Climate cannot be considered a satisfactory indicator of actual conditions since it is based upon a vast number of elements taken as an average. 

[ Back to Top ]

·  Cloud Base

For a given cloud or cloud layer, it is the lowest level in the atmosphere where cloud particles are visible. 

[ Back to Top ]

·  Cold-air Funnel

A funnel cloud or (rarely) a small, relatively weak tornado that can develop from a small shower or thunderstorm when the air aloft is unusually cold (hence the name.  They are much less violent than other types of tornadoes. 

[ Back to Top ]

·  Cumulonimbus Cloud

A vertically developed cloud, often capped by an anvil shaped cloud.  Also called a thunderstorm cloud, it is frequently accompanied by heavy showers, lightning, thunder, and sometimes hail or gusty winds.  

[ Back to Top ]

·  Cumulus Cloud

A cloud in the shape of individual detached domes, with a flat base and a bulging upper portion resembling cauliflower. 

[ Back to Top ]

·  Debris Cloud

A rotating "cloud" of dust or debris, near or on the ground, often appearing beneath a condensation funnel and surrounding the base of a tornado. 

[ Back to Top ]

·  Depression

A region of low atmospheric pressure that is usually accompanied by low clouds and precipitation. 

[ Back to Top ]

·  Derechoe

A widespread and usually fast-moving windstorm associated with convection.  Derechoes include any family of downburst clusters produced by an extratropical mesoscale convective system (MCS) and can produce damaging straight-line winds over areas hundreds of miles long and more than 100 miles across. 

[ Back to Top ]

·  Dew point

The temperature to which the air must be cooled for water vapor to condense and form fog or clouds. 

[ Back to Top ]

·  Downburst

A strong downdraft resulting in an outward burst of damaging winds on or near the ground.  Downburst winds can produce damage similar to a strong tornado. 

[ Back to Top ]

·  Downdraft

A column of generally cool air that rapidly sinks to the ground, usually accompanied by precipitation as in a shower or thunderstorm.

[ Back to Top ]

·  Drought

Abnormally dry weather in a region over an extended period, sufficient to cause a serious hydrological (water cycle) imbalance in the affected area.  This can cause such problems as crop damage and water-supply shortage. 

[ Back to Top ]

·  El Nino

A major warming of the equatorial waters in the eastern Pacific Ocean.  El Nino events usually occur every 3 to 7 years, and are related to shifts in global weather patterns.  

[ Back to Top ]

·  Evaporation

The process of a liquid changing into a vapor or gas. 

[ Back to Top ]

·  Fahrenheit

The standard scale used to measure temperature in the United States, in which the freezing point of water is thirty-two (32) degrees and the boiling point is two hundred and twelve (212) degrees. 

[ Back to Top ]

·  Flood

A condition that occurs when water overflows the natural or artificial confines of a stream or river; the water also may accumulate by drainage over low-lying areas. 

[ Back to Top ]

·  Front

The boundary or transition zone between two different air masses.  The basic frontal types are cold fronts, warm fronts and occluded fronts. 

[ Back to Top ]

·  Fujita Scale

System developed by Dr. Theodore Fujita to classify tornadoes based on wind damage.  Scale is from F0 for weakest to F5 for strongest tornadoes. 

[ Back to Top ]

·  Funnel Cloud

A rotating, cone-shaped column of air extending downward from the base of a thunderstorm but not touching the ground.  When it reaches the ground it is called a tornado. 

[ Back to Top ]

·  Gustnado (or Gustinado)

Gust front tornado, usually weak and short lived, that occurs along the gust front of a thunderstorm.   Often it is visible only as a debris cloud or dust whirl near the ground.

[ Back to Top ]

·  Hail

Precipitation in the form of balls or irregular lumps of ice produced by liquid precipitation, freezing and being coated by layers of ice as it is lifted and cooled in strong updrafts of thunderstorms.  

[ Back to Top ]

·  High

An area of high pressure, usually accompanied by anticyclonic and outward wind flow.  Also known as an anticyclone. 

[ Back to Top ]

·  Hook Echo

A radar pattern sometimes observed in the southwest quadrant of a tornadic thunderstorm.  Appearing like a fishhook turned in toward the east, the hook echo is precipitation aloft around the periphery of a rotating column of air 2-10 miles in diameter.  

[ Back to Top ]

·  Hygrometer

An instrument used to measure humidity. 

[ Back to Top ]

·  Inflow Bands (or Feeder Bands)

Bands of low clouds, arranged parallel to the low-level winds and moving into or toward a thunderstorm. 

[ Back to Top ]

·  Inflow Jets

Local jets of air near the ground flowing inward toward the base of a tornado. 

[ Back to Top ]

·  Instability

A state of the atmosphere in which convection takes place spontaneously, leading to cloud formation and precipitation. 

[ Back to Top ]

·  Isobar

A line of equal barometric pressure on a weather map. 

[ Back to Top ]

·  Jet Stream

Strong winds concentrated within a narrow band in the upper atmosphere.  It normally refers to horizontal, high-altitude winds.  The jet stream often "steers" surface features such as front and low pressure systems. 

[ Back to Top ]

·  Knot

A measure of speed.  It is one nautical mile per hour (1.15 mph).  A nautical mile is one minute of one degree of latitude. 

[ Back to Top ]

·  La Nina

A cooling of the equatorial waters in the Pacific Ocean. 

[ Back to Top ]

·  Leeward

Situated away from the wind; downwind - opposite of windward. 

[ Back to Top ]

·  Lightning

Any form of visible electrical discharges produced by thunderstorms. 

[ Back to Top ]

·  Low

An area of low pressure, usually accompanied by cyclonic and inward wind flow.  Also known as a cyclone. 

[ Back to Top ]

·  Macroburst

Large downburst with a 2.5 mile or greater outflow diameter and damaging winds lasting 5 to 20 minutes. 

[ Back to Top ]

·  Mamma Clouds

Also called mammatus, these clouds appear as hanging, rounded protuberances or pouches on the under-surface of a cloud.  With thunderstorms, mammatus are seen on the underside of the anvil.  These clouds do not produce tornadoes, funnels, hail, or any other type of severe weather, although they often accompany severe thunderstorms. 

[ Back to Top ]

·  Mesocyclone

A storm-scale region of rotation, typically around 2-6 miles in diameter and often found in the right rear flank of a supercell (or often on the eastern, or front, flank of an high percipitation storm).  The circulation of a mesocyclone covers and area much larger than the tornado that may develop within it. 

[ Back to Top ]

·  Microburst

A strong localized downdraft from a thunderstorm with peak gusts lasting 2 to 5 minutes. 

[ Back to Top ]

·  Millibar

A metric unit of atmospheric pressure. 1 mb = 100 Pa (pascal).  Normal surface pressure is approximately 1013 millibars. 

[ Back to Top ]

·  Multicell Cluster Thunderstorm

A thunderstorm consisting of two or more cells, of which most or all are often visible at a given time as distinct domes or towers in various stages of development. 

[ Back to Top ]

·  Multivortex Tornado

A tornado in which two or more condensation funnels or debris clouds are present at the same time, often rotating about a common center or about each other.  Multi-vortex tornadoes can be especially damaging. 

[ Back to Top ]

·  Outflow

Air that flows outward from a thunderstorm. 

[ Back to Top ]

·  Outflow Boundary

A storm-scale or mesoscale boundary separating thunderstorm-cooled air (outflow) from the surrounding air;; similar in effect to a cold front, with passage marked by a wind shift and usually a drop in temperature.  

[ Back to Top ]

·  Precipitation

 Liquid or solid water that falls from the atmosphere and reaches the ground.

[ Back to Top ]

·  Prevailing Wind

The direction from which the wind blows most frequently in any location. 

[ Back to Top ]

·  Radar

An instrument used to detect precipitation by measuring the strength of the electromagnetic signal reflected back. (RADAR = Radio Detection and Ranging). 

[ Back to Top ]

·  Rain-Free Base

A horizontal, dark cumulonimbus base that has no visible precipitation beneath it.  This structure usually marks the location of the thunderstorm updraft.  Tornadoes most commonly develop from wall clouds that are attached to the rain-free base, or from the rain-free vase itself.  This is particularly true when the rain-free base is observed to the south or southwest of the precipitation shaft. 

[ Back to Top ]

·  Rain Guage

An instrument used to measure rainfall amounts. 

[ Back to Top ]

·  Relative Humidity

The amount of water vapor in the air, compared to the amount the air could hold if it was totally saturated (Expressed as a percentage). 

[ Back to Top ]

·  Saturation

A condition of the atmosphere in which a certain volume of air holds the maximum water vapor it can hold at a specific temperature. 

[ Back to Top ]

·  Scud Clouds

Small, ragged, low cloud fragments that are unattached to a larger cloud base and often seen with and behind cold fronts and thunderstorm gust fronts.  Such clouds generally are associated with cool moist air, such as thunderstorm outflow. 

[ Back to Top ]

·  Severe Thunderstorm

A strong thunderstorm with wind gusts in excess of 58 mph (50 knots) and / or hail with a diameter of 3/4" or more.  A thunderstorm with winds of greater than 39 mph and / or hail greater than 1/2 inch is defined as approaching severe. 

[ Back to Top ]

·  Shelf Cloud

A low-level horizontal accessory cloud that appears to be wedge-shaped as it approaches.  it is usually attached to the thunderstorm base and forms along the gust front.  The leading edge of the shelf is often smooth and at times layered or terraced.  It is most often seen along the leading edge of an approaching line of thunderstorms, accompanied by gusty straight winds as it passes overhead and followed by precipitation.  The underside is concave upward, turbulent, boiling or wind-torn.  Tornadoes rarely occur with the shelf cloud.

[ Back to Top ]

·  Squall

A strong wind characterized by a sudden onset in which the wind speed increases at least 16 knots (18.5 mph) and is sustained at 22 knots (25 mph) or more for at least one minute.

[ Back to Top ]

·  Squall Line

Any non-frontal line or narrow band of active thunderstorms.  The term is usually used to describe solid or broken lines of strong or severe thunderstorms. 

[ Back to Top ]

·  Straight Line Winds

Thunderstorm winds most often found with the gust front.  They originate from the downdrafts and can cause damage which occurs in a "straight line", as opposed to tornadic wind damage which has circular characteristics.

[ Back to Top ]

·  Supercell Thunderstorm

A severe thunderstorm whose updrafts and downdrafts are in near balance allowing the storm to maintain itself for several hours.  Supercells often produce large hail and tornadoes. 

[ Back to Top ]

·  Sustained Winds

The wind speed obtained by averaging the observed values over a one minute period. 

[ Back to Top ]

·  Tail Cloud

A low tail-shaped cloud extending outward from the northern quadrant of a wall cloud.  Motions in the tail cloud are toward the wall cloud with rapid updraft at the junction of tail and wall cloud.  This horizontal cloud is not a funnel or tornado. 

[ Back to Top ]

·  Thunder

The sound caused by a lightning stroke as it heats the air and causes it to rapidly expand. 

[ Back to Top ]

·  Thunderstorm

A storm with lightning and thunder, produced by a cumulonimbus cloud, usually producing gusty winds, heavy rain and sometimes hail. 

[ Back to Top ]

·  Tornado

A violent rotating column of air, in contact with the ground, pendant from a cumulonimbus cloud.  A tornado does not require the visible presence of a funnel cloud.  It has a typical width of tens to hundreds of meters and lifespan of minutes to hours. 

[ Back to Top ]

·  Trough

An elongated area of relatively low atmospheric pressure surface or aloft.  Usually not associated with a closed circulation, and thus used to distinguish from a closed low.  The opposite of ridge. 

[ Back to Top ]

·  Twister

A colloquial term for a tornado. 

[ Back to Top ]

·  Updraft

A small-scale current of rising air.  This is often associated with cumulus and cumulonimbus clouds. 

[ Back to Top ]

·  Vertical Shear

The rate of change of wind speed or direction, with a given change in height. 

[ Back to Top ]

·  Virga

Precipitation falling from the base of a cloud and evaporating before it reaches the ground. 

[ Back to Top ]

·  Vortex

An atmospheric feature that tends to rotate.  It has vorticity and usually has closed streamlines. 

[ Back to Top ]

·  Wall Cloud

A local and often abrupt lowering of a rain-free cumulonimbus base into a low-hanging accessory cloud, for 1 to 4 miles in diameter.  The wall cloud is usually situated in the southwest portion of the storm below an intense updraft marked by the main cumulonimbus cloud and associated with a very strong or severe thunderstorm.  When seen from several miles away, many wall clouds exhibit rapid upward motion and rotation in the same sense as a tornado, except with considerably lower speed.  A rotating wall cloud usually develops before tornadoes or funnel clouds by a time which can range from a few minutes up to possibly an hour.

[ Back to Top ]

·  Warning

Forecast issued when a particular weather or flood hazard is "imminent" or already occurring (e.g., tornado warning, flash flood warning, severe thunderstorm warning).  A warning is used for conditions posing a threat to life or property.

[ Back to Top ]

·  Watch

Forecast issued well in advance to alert the public of the possibility of a particular weather related hazard (e.g. tornado watch, flash flood watch, severe thunderstorm watch).  The occurrence, location and timing may still be uncertain. 

[ Back to Top ]

·  Weather

State of the atmosphere with respect to heat or cold, wetness or dryness, calm or storm, clearness or cloudiness.  Also, weather is the meteorological day-to-day variations of the atmosphere and their effects on life and human activity.  It includes temperature, pressure, humidity, clouds, wind, precipitation and fog.

[ Back to Top ]

·  Wedge (or Wedge Tornado)

A large tornado with a condensation funnel that is at least as wide (horizontally) at the ground as it is tall (vertically) from the ground to cloud base. 

[ Back to Top ]

·  Wind Chill

The additional cooling effect resulting from wind blowing on bare skin.  The wind chill is based on the rate of heat loss from exposed skin caused by the combined effects of wind and cold.  The (equivalent) wind chill temperature is the temperature the body "feels" for a certain combination of wind and air temperature. 

[ Back to Top ]

·  Wind Direction

The direction from which the wind is blowing. 

[ Back to Top ]

·  Wind Shear

Variation in wind speed and/or direction over a short distance.  Shear usually refers to vertical wind shear, i.e., the change in wind with height, but the term also is used in Doppler radar to describe changes in radial velocity over short horizontal distances. 

[ Back to Top ]

·  Wind Vane

An instrument that determines the direction from which a wind is blowing. 

[ Back to Top ]

·  Where can I find more weather terms?

This is a short list of weather terms that can be found at the National Weather Service website. 

[ Back to Top ]



 
Page Generation: 0.14 Seconds

:: fisubice phpbb2 style by Daz :: PHP-Nuke theme by www.nukemods.com ::
:: fisubice Theme Recoded To 100% W3C CSS & HTML 4.01 Transitional & XHTML 1.0 Transitional Compliance by RavenNuke™ TEAM ::

:: W3C CSS Compliance Validation :: W3C HTML 4.01 Transitional Compliance Validation :: W3C XHTML 1.0 Transitional Compliance Validation ::