What is humidity? What’s a barometer and what does it tell us about the weather?
Answers to these and other commonly asked questions about the lingo Meteorologists use can be found below in ABC-7’s “Weather Talk” Definitions.
Advection – transport of an atmospheric property (such as temperature or moisture) by the wind.
Air Mass – a widespread body of air that has the same temperature and moisture distribution.
Alberta Clipper – a fast moving low pressure system that forms over Alberta, Canada. It usually has low moisture content but in the winter, it may bring significant snowfall to the Midwest and East Coast.
Almanac – a calendar with astronomical and meteorological data.
Altitude – a measure of height above the earth’s surface or above mean sea level; measured by an altimeter.
Anemometer – an instrument used to measure wind speed.
Arroyo – a small water carved channel or gully with steep banks usually present in an arid environment and most often dry due to infrequent rainfall.
Atmosphere – the air surrounding and bound to the Earth.
Atmospheric Pressure – the pressure exerted by the Earth’s atmosphere at any given point; measured by a barometer.
Autumnal (Fall) Equinox – marks the astronomical start of autumn in the Northern Hemisphere. This day usually occurs on September 20th or 21st each year. It is marked by equal amounts (12 hours) of daylight and night.
Back Door Cold Front – a cold front moving in from the East, instead of the west, here in the borderland.
Backing – a counterclockwise shift in the wind direction (for example, east winds shifting north).
Barometer – an instrument that measures atmospheric pressure.
Blizzard – a winter storm, lasting three hours or more, with winds greater than 35 miles per hour and considerable snow fall.
Breezy – 15 to 25 mile per hour winds; synonymous with blustery.
Celsius – a temperature scale in which 0 degrees is the freezing point of water and 100 degrees is the boiling point. To convert a Fahrenheit temperature to Celsius, subtract 32 and then multiply by 5/9.
Cirrus – high level, “wispy-looking” clouds.
Climate – the generally prevailing weather conditions of a particular region, throughout the year, averaged over a series of years (typically 30 years).
Climate Change – a non-random change in climate measured over several decades due to natural or human-induced causes.
Cold Front – an area where cold air is replacing warm air.
Condensation – the process in which vapor (or gas) becomes a liquid.
Convection – the vertical transport of heat and moisture in the atmosphere; thunderstorms are one kind of convection.
Cumulus – detached, generally dense clouds with sharp outlines.
Cyclone – an area of low pressure in which winds blow inward in a counter-clockwise circulation.
Dew – moisture that has condensed on objects near the ground.
Dewpoint – the temperature to which air must be cooled in order for saturation to occur. That is, for dew or frost to form.
Disturbance – a disruption of the atmosphere. This usually refers to an area of low pressure and thus is associated with inclement weather.
Drizzle – precipitation in the form of water droplets smaller than 0.5 millimeters. (Drops larger than 0.5 millimeters are referred to as rain.)
Drought – a deficiency in moisture that results in adverse impacts on people, vegetation and animals.
Dust Storm – a severe weather condition characterized by strong winds and dust filled air over an extensive area. Dust Storms are frequent around the borderland during the spring. Watch ABC-7 for your Exclusive Dust Cast.
El Nino – a warming in the average sea surface temperature in the eastern tropical Pacific that usually lasts 9-12 months and results in wetter than normal conditions for the southern states.
Evaporation – the process in which a liquid becomes a vapor (or gas).
Fahrenheit – the standard temperature scale in the United States. On this scale, water freezes at 32 degrees and boils at 212 degrees.
Flash Flood – a flood that results from intense rainfall over a small area and rises rapidly with little or no advance warning.
Flash Flood Warning – issued when flash flooding is occurring or will imminently occur in the specified area.
Flash Flood Watch – issued when flash flooding is possible in the specified area.
Flurries – short lasting, intermittent light snowfall with no measurable accumulation.
Freezing Point – 32 degrees Fahrenheit or 0 degrees Celcius.
Front – the transition zone between two air masses.
Frost – ice crystals that form on the earth’s surface or on other objects when the temperature drops below 32 degrees Fahrenheit.
Global Warming – an overall increase in the average global temperature which may be caused by additional heat being trapped by greenhouse gases (water vapor, methane, carbon dioxide and ozone).
Gulf Stream – a warm, swift, relatively narrow ocean current that flows along the east coast of the United States.
Gusts – a rapid fluctuation of wind speed.
Hail – precipitation in the form of balls or lumps of ice.
Heat Index (apparent temperature) – an accurate measure of how hot it really feels when the relative humidity is factored in the actual air temperature.
Heat Exhaustion – a mild form of heat stroke characterized by heaving sweating, dizziness and faintness.
Heat Stroke – a condition resulting from excessive exposure to intense heat characterized by high fever, collapse and sometimes convulsions or coma.
Heat Wave – a period of abnormally hot and/or humid weather typically lasting 2 or more days.
High Pressure Area – an area of maximum barometric pressure usually associated with relatively warm and dry weather.
Humidity – a measure of the water vapor content of air; usually expressed as a percentage of the moisture in air compared to what it is able to hold at a given temperature.
Hurricane – a cyclone that originates over tropical oceans and has torrential rains and winds greater than 75 miles per hour.
Instability – an atmospheric state where air rises and forms clouds which may cause rain.
Inversion – a reversal in the usually decrease in temperature with increasing height. An inversion layer is the layer of the atmosphere, typically closest to the ground, in which this occurs.
Jet Stream – a zone of winds, concentrated in the upper atmosphere, which blow from west to east in the northern hemisphere. These winds act as the “steering wheel” for our weather systems.
Knots – a unit of speed used for aviation and marine purposes; 1 knot (1 nautical mile per hour) = 1.15 miles per hour.
La Nina - a cooling in the average sea surface temperature in the eastern tropical Pacific that results in drier than normal conditions for the southern states.
Lake Effect Snow – snow showers created when cold, dry air passes over warm, moist lake (Great Lakes) picking up moisture and heat.
Lightning – a visible electric discharge from a thunderstorm.
Low Pressure Area – an area of minimum barometric pressure usually associated with inclement weather.
Meteorology – the science dealing with the atmosphere and its phenomena.
Monsoon – a name for seasonal winds. The southwestern states experience the “Mexican Monsoon” or the “North American Monsoon” in the summer months when winds shift to a more southerly direction. This shift in the winds allows moisture to flow in from the Baja which increases the humidity and helps in the development of thunderstorms.
Nor ‘easter – a strong low pressure system that affects the Mid Atlantic and New England States in the winter months.
NWS – National Weather Service.
Outflow – air that flows outward from a thunderstorm.
Overcast – term used to describe the sky when it is more than 95% covered by clouds.
Ozone Action Day – a “heads up” message issued when ozone levels in that atmosphere are expected to reach dangerous levels. This message encourages people to help prevent air pollution by not using gas powered machines such as lawn mowers and cars.
Ozone Layer – an atmospheric layer containing oxygen in the form of ozone that filters incoming ultraviolet radiation from the sun.
POP – probability of precipitation.
Precipitation – refers to all liquid and solid forms of water particles that fall from the atmosphere to the ground including rain, snow, hail, etc.
RADAR – an acronym for RAdio Detection And Ranging; Doppler Radar is used in meteorology for detecting the location and movement of storms.
Radiosonde – an instrument, carried aloft by weather balloons typically launched twice a day, that collects information about the present state of the atmosphere including temperature, pressure and humidity and sends it back through a small, expendable radio transmitter.
Rain – precipitation in the form of water droplets larger than 0.5 millimeters. (Drops smaller than 0.5 millimeters are referred to as drizzle.)
Red Flag Warning – issued by the National Weather Service when critical fire weather conditions exist indicating the potential for explosive wildfire growth. These conditions include low humidity, warm temperatures, and winds greater than 15 mph.
Ridge – an elongated area of relatively high atmospheric pressure.
Severe Thunderstorm – a thunderstorm with winds greater than 58 miles per hour and/or hail greater than 0.75” in diameter.
Severe Thunderstorm Warning – issued when a severe thunderstorm has by sighted or indicated by radar in the specified area.
Severe Thunderstorm Watch – issued when severe thunderstorms are possible in the specified area.
Shower – precipitation that is characterized by rapid starts and stops or by rapid changes in intensity.
Snow – precipitation in the form of white or translucent ice crystals.
Stable – an atmospheric state where warm air traps cold air near the surface and inhibits vertical movement of air.
Stationary Front – a zone between two air masses that shows little or no movement.
Stratus – a low, generally gray cloud layer with a fairly uniform base. Fog is usually a surface-based form of stratus.
Storm Track – the path that a low pressure area or storm follows.
Summer Solstice – the day at which the sun is farthest north in the Northern Hemisphere; marks the astronomical start of summer in the Northern Hemisphere typically on June 20th or 21st.
Temperature – a measure of the internal energy that a substance contains.
Thunder – the sound caused by rapidly expanding gases in a lightning discharge.
Thunderstorm – a local storm produced by a cumulonimbus cloud and accompanied by lightning and thunder.
Tornado – a violent, rotating column of air extending to the ground from a thunderstorm.
Tornado Warning – issued when a tornado has been reported or is indicated by radar in the specified area.
Tornado Watch – issued when tornadoes are possible in the specified area.
Tropical Air – warm, humid air that originates over tropical and subtropical areas.
Trough – an elongated area of relatively low atmospheric pressure.
Typhoon – a hurricane that forms in the Western Pacific.
Unstable Air – air that is able to easily rise and has the potential to produce clouds, rain and thunderstorms.
Vernal (Spring) Equinox - marks the astronomical start of spring in the Northern Hemisphere. This day usually occurs on March 20th or 21st each year. It is marked by equal amounts (12 hours) of daylight and night.
Virga – water falling from a cloud that evaporates before it hits the ground.
Visibility – the greatest distance in a given direction at which it is just possible to see and identify with the naked eye.
Warm Front – a zone where warm air is replacing cold air.
Waterspout – a tornado that forms over water.
Weather – the state of the atmosphere.
Wind – air in motion relative to the earth’s surface.
Wind Chill Factor – the cooling effect caused by temperature and wind on bare skin.
Wind Direction – the compass direction from which the wind is blowing.
Winter Solstice – the day at which the sun is furthest south in the Southern Hemisphere; marks the astronomical start of winter in the Northern Hemisphere typically on December 20th or 21st.
Winter Storm Warning – a winter storm is imminent.
Winter Storm Watch – a winter storm is possible.
Wx – an abbreviation for “weather”.
Zonal Flow – large-scale atmospheric flow in which the east-west component is dominant.
