Meteorology- This is the study of the Earth's atmosphere. A
meteorologist is someone who studies the atmosphere. Physical
meteorology deals with the physical aspects of the atmosphere,
such as the formations of clouds, rain, thunderstorms, and
lightning. Synoptic meteorology is the study and anlysis of
large weather systems that exist for more than one day.
Weather forecasting is one part of Synoptic meteorology.
Precipitation- Rain or snow with a pH value of less than 5.6.
Adibiatic Temperature Change- A cooling or heating of the air
caused by expansion of contraction of air molecules, as
opposed to the gain or loss of heat. For example, adiabatic
cooling takes place as air rises.
Advection- Horizontal movement of air, moisture, or heat.
Advection Fog- Fog formed by warm, humid air flowing over
colder ground or water.
Air Mass- A
large body of air with nearly uniform temperature and moisture
Airstream- A significant body of air flowing in the same
Alberta Clipper- A small, fast-moving low-pressure system that
forms in western Canada and travels southeastward into the
United States. These storms, which generally bring little
precipitation, generally precede an Arctic air mass.
Altitude- Height expressed as the distance above a reference
point, which is normally sea level or ground level.
Anemometer- An instrument that measures wind speed.
Aneroid Barometer- An instrument built around a metal
structure that bends with changing air pressure. These changes
are recorded on a pointer that moves back and forth across a
Anti-Cyclone- A high-pressure system featuring clock-wise
Arctic Air- A mass of very dry, very cold air that develops
over the snow-and-ice-covered regions of the Far North.
Atmosphere- The mass of air surrounding the Earth.
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-Door Cold Front- A cold front that moves in from the
northeast, rather than from the normal north or northwest
Backing Wind- Shifting of the wind in a counterclockwise
direction, usually resulting from the approach of a
Barograph- An instrument that provides a continuous record of
Barometer- An instrument for measuring atmospheric pressure.
Barometric Tendency- The amount and direction of change in
barometer readings over a three-hour period.
Beaufort Wind Scale- A system used to classify wind speed,
developed in 1805 by British Admiral Francis Beaufort.
Blizzard- A severe snow storm featuring sustained winds of
more than 32 miles per hour, temperatures 10 degrees
Fahrenheit or lower, and visibility of 500 feet or less.
Ceiling- The height above the ground of the base of the lowest
layer of clouds, when at least 60 percent of the sky is
covered by clouds.
Celsius Temperature Scale (also known as Centigrade
Temperature Scale)- A temperature scale in which 0 degrees is
the melting point of ice and 100 degrees is the boiling point
Circulation- The pattern of the movement of air. General
circulation is the flow of air of large, semi-permanent
weather systems, while secondary circulation is the flow of
air of more temporary weather systems.
Climate- A statistical portrait of weather conditions in a
specific place over a long period.
Climatology- The study of climate.
Cloudburst- A sudden, intense rainfall that is normally of
Cold Front- The leading edge of a colder mass of air that
displaces a warmer mass of air.
Condensation- The change of vapor to liquid.
Condensation Nuclei- Small particles in the air around which
water vapor condenses.
Conduction- The transfer of heat by molecular action within a
substance or when two substances are in direct contact.
Continental Air Mass- An air mass that forms over land. It is
usually dry, but may be cold or warm.
Contrail- A cloud-like stream formed in cold, clear air behind
the engines of an airplane.
Convection- The transfer of by movement of the heated
material. In meteorology, it is often used to indicate the
vertical movement of warm air (as opposed to advection, the
Coriolis Effect- The curving motion of anything, such as air,
caused by the rotation of the Earth.
Cyclone- A low-pressure system in which winds spin inward in a
counterclockwise direction in the northern hemisphere.
Depression- An area of low atmospheric temperature.
Dew- Water that condenses onto grass and other objects near
Dew Point- The temperature to which a certain volume of air
must be cooled to bring the relative humidity to 100 percent.
Disturbance- An area of low-pressure in which storm conditions
Doppler Radar- Sophisticated radar that can measure the speed
and direction of moving objects, such as wind.
Downburst- A sudden, strong, downward blast of air, usually
from a thundercloud.
Drizzle- Precipitation featuring tiny water droplets, no more
than .02 inches in diameter.
Drought- Abnormally dry weather in a region over an extended
Dust Devil- A small, whirling column of wind that picks up
dirt and other loose material as it travels.
El Niņo- Linked ocean and atmospheric events, which have
worldwide effects, characterized by warming of the water in
the tropical Pacific from around the International Date Line
to the coast of Peru.
Equinox- The twice-yearly occurrence (about March 21 and
September 21) when the sun at its highest point crosses the
Extratropical Cyclone- A cyclone that forms outside of the
Evaporation- The change in a substance from a liquid or solid
state to a gaseous state.
Eye- The roughly circular area of relatively calm weather at
the center of a hurricane.
Fahrenheit Temperature Scale- A temperature scale that uses 32
degrees as the melting point of ice and 212 degrees as the
boiling point of water.
Flash Flood- Flooding caused by a rapid rise in the water
level of rivers, streams, or lakes, usually as a result of
Fog- A cloud of water droplets suspended in the air that
touches the ground.
Freezing- The change in a substance from a liquid to a solid
Freezing Nuclei- Particles suspended in the air around which
ice crystals form.
Freezing Rain- Supercooled drops of water that turn to ice
when they hit a cold surface.
Front- The boundary between two different air masses.
Frost- Ice crystals that form on grass and other objects when
the temperature and dew point fall below freezing.
Fujita Scale- A scale for estimating damage caused by the
winds of a tornado, developed by Theodore Fujita.
Glaze- A smooth coating of ice formed when supercooled water
droplets spread out on a surface before freezing.
Graupel- Precipitation formed when water droplets freeze in
layers around a falling ice crystal.
Greenhouse Effect- The warming that takes place when molecules
in the atmosphere trap heat radiating away from the surface
and redirect it back toward Earth.
Gulf Stream- A warm ocean current that flows from the Gulf of
Mexico across the Atlantic to the coast of western Europe.
Gust- A sudden, brief increase in wind speed.
Hail- Chunks of ice that form in layers in the updrafts of
Halo- A ring or arc of light around the sun or moon that is
caused by ice crystals in the atmosphere.
Haze- Particles or fine dust suspended in the air that produce
Heat Index- This index is a measure of the contribution that
high humidity makes with abnormally high temperatures in
reducing the body's ability to cool itself.
Heat Lightning- Lightning that can be seen, but is too far
away to be heard.
High- An area of higher atmospheric pressure.
Hurricane- A tropical cyclone in the western hemisphere that
has sustained wind speeds of 74 miles per hour or greater.
Hydrosphere- The Earth's water.
Hygrometer- An instrument that measures the water vapor
content of the air.
Ice Crystals- Frozen water vapor suspended in the air.
Instability- A state of the atmosphere in which convection
takes place spontaneously, leading to cloud formation and
Inversion- A condition in which air near the ground is cooler
than air above it....a condition opposite the normal decrease
in temperature with height.
Isobar- A line on a weather map that surrounds an area with
the same atmospheric pressure.
Isotherm- A line on a weather map that surrounds an area with
the same temperature.
Jet Stream- A narrow band of winds blowing high in the
troposphere at speeds in excess of 57 miles per hour or
Kelvin Temperature Scale- A temperature scale in which 0
degrees is the point at which all molecular motion ceases
Kilopascal- A metric unit of air pressure. It is simply
millibars divided by 10.
Latent Heat- The energy that is stored when water evaporates.
This energy is released when water condenses as a liquid or
Lifting- The forcing of air in a vertical direction by an
upslope in terrain or by the movement of a denser air mass.
Lightning- An electrical discharge produced by a thunderstorm.
Low- An area of low atmospheric pressure.
Maritime Air Mass- An air mass that forms over water. It is
usually humid, and may be cold or warm.
Mean Temperature- The average of a series of temperatures
taken over a period of time, such as a day or a month.
Mercury Barometer- An instrument that measures barometric
pressure by measuring the level of mercury in a column.
Mesocyclone- A large, rotating column of air that forms in a
violent thunderstorm and may spawn tornadoes.
Microburst- A downburst from a thunderstorm that is confined
to a small area.
Mid-Latitudes- The areas in the northern and southern
hemispheres between the tropics and the Arctic and Antarctic
Millibar- A metric unit of air pressure measurement.
Monsoon- A wind that in summer blows from the sea to a
continental interior, bringing copious rains.
"Next Generation Weather Radar," a system now being installed
across the country by the U.S. Weather Service, the Federal
Aviation Administration, and the Department of Defense.
Nor'easter- A low-pressure disturbance forming along the South
Atlantic coast and moving northeast along the Middle Atlantic
and New England coasts to the Atlantic Provinces of Canada.
Also called a Northeaster or Coastal Storm.
Normal- A numerical figure representing the average of
conditions at a location over a period of years.
Numerical Forecasting- Forecasting the weather through digital
computations carried out by supercomputers.
Occluded Front- A boundary between cold and warm air masses
that acts like a cold front in some areas and a warm front in
Orographic Lifting- The upward flowing of air caused by rising
terrain, such as a mountain range.
Overrunning- The flow of warm air over cold air in advance of
a warm front.
Ozone- An unstable oxygen compound that is a pollutant at
ground level, but that absorbs deadly ultraviolet rays in the
Ozone Hole- A thinning of the ozone layer over Antarctica,
which occurs each spring.
Polar Air- A mass of very cold, very dry air that forms in
Precipitation- Any liquid or solid form of water that falls
from the atmosphere and reaches the surface of the Earth.
Pressure Gradient Force- Force acting on air that causes it to
move from areas of higher pressure to areas of lower pressure.
Prevailing Wind- The direction from which the wind blows most
frequently in any location.
Psychrometer- An instrument that measures relative humidity of
Radar- Stands for "radio detection and ranging." An instrument
that detects and ranges distant objects by measuring the
scattering and reflection of radio beams.
Radiation- The transferring of energy through electromagnetic
Rain- Liquid precipitation with drops larger than .02 inches
Rainbow- An arc or circle of colored light caused by the
refraction of light by water droplets in the air.
Refraction- The bending of light as it passes through areas of
different density, such as from air through ice crystals.
Relative Humidity- A measure of the amount of water vapor
actually held by a specific volume of air in comparison to the
maximum water vapor that air could hold at a constant
Ridge- An elongated area of high pressure that normally runs
north and south.
Rime- Tiny balls of ice that form when tiny drops of water
freeze on contact with the surface.
Saffir-Simpson Hurricane Damage Potential Scale- A scale that
measures hurricane intensity, developed by Herbert Saffir and
Saturation- A condition of the atmosphere in which a certain
volume of air holds the maximum water vapor it can hold at a
Secondary Cold Front- A front that follows a primary cold
front and ushers in even colder air.
Shower- Snowfall or rainfall or brief duration that can either
be heavy or light.
Sleet- Precipitation consisting of ice particles formed when
Smog- Air pollution caused by a mixture of smoke and fog.
Snow- Precipitation consisting of clumps of ice crystals.
Solar Energy- The energy produced by the sun.
Solstice- The time of year when the sun is the farthest north
or the farthest south (about June 21 and December 21).
Squall Line- A line of thunderstorms that forms along a front.
Stable Air- Air in which temperature and humidity at various
levels discourage the formation of convection currents.
Stationary Front- The border between cold and warm air masses
that are not moving.
Storm Track- The path that storms generally follow in a given
Sublimation- The change of water vapor directly into ice
crystals or ice crystals directly into water vapor.
Supercell Thunderstorm- An unusually violent thunderstorm that
is capable of generating tornadoes.
Subsidence- The descent of a body of air, usually in a high
pressure area, that warms the lower levels of air.
Supercooled Water- Water cooled to a temperature of less than
32 degrees Fahrenheit without freezing.
Thermometer- An instrument for measuring temperature.
Temperate Zone- The area of the globe between the tropics and
the polar regions.
Thunder- The sound produced by lightning discharges.
Thunderstorms- Storms that produce lightning and thunder.
Tornado- A violently rotating column of air that reaches from
the base of a cloud to the ground.
Tropics- The area of the globe from latitudes 23.5 degrees
north to 23.5 degrees south.
Tropical Air- Warm, humid air masses that form in tropical
Tropical Cyclone- A low-pressure system that forms in the
Tropical Depression- A tropical cyclone with winds that do not
exceed 38 miles per hour.
Tropical Storm- A tropical cyclone with winds of 39-73 miles
Trough- An elongated low-pressure system that generally
stretches north and south.
Typhoon- A tropical cyclone with winds of 74 miles per hour or
greater that occurs west of the International Date Line.
Unstable Air- Air with temperature differences that encourage
the formation of convection currents that can produce clouds
Updraft- An upward current of air, usually within a
Veering Winds- Winds that shift in a clockwise direction, a
shift caused by a high-pressure system.
Visibility- The greatest distance at which one can see and
Virga- Water droplets or ice crystals that fall from high
clouds but that evaporate before hitting the ground.
Warm Front- The leading edge of a mass of warmer air that
displaces a mass of colder air.
Warning- A threatening weather condition is occuring as
indicated by a radar or spotter, or is expected to occur or
strike an area very soon.
Watch- Conditions are favorable for a certain threatening
weather condition to occur. It doesn't mean the threatening
weather condition is occuring.
Waterspout- A tornado-like formation over water, usually much
smaller and less vigorous than a true tornado. Waterspouts
tend to occur most frequently in tropical waters, although
they have been observed on the Great Lakes and on other
northern lakes in Canada and the United States.
Water Vapor- The invisible gaseous form of water.
Wave- A small cyclonic circulation in the early stages of
development that moves along a cold front.
Weather- The conditions in the atmosphere at any given time.
Wind- Air in motion that moves relatively horizontally in
relationship to the surface of the Earth.
Windchill Factor- A measure of the effect of wind in
increasing the heat loss from exposed flesh.
Wind Direction- The direction from which the wind is blowing.
Wind Shear- A sudden shift in wind direction.