# Glossary of meteorology

(Redirected from Meteorological phenomena)

This glossary of meteorology is a list of terms and concepts relevant to meteorology and the atmospheric sciences, their sub-disciplines, and related fields.

## A

The horizontal transport of some property of the atmosphere or ocean, such as thermal energy, humidity, or salinity. In the context of meteorology, the related term convection generally refers to vertical transport.
actinoform
actinometer
Any idealized hypothetical process by which energy is transferred between a thermodynamic system and its surroundings only as work, without a corresponding transfer of heat or mass. In the context of meteorology, the assumption of adiabatic isolation is often used to explain the processes of adiabatic heating and adiabatic cooling, which involve changes in temperature as a parcel of air is compressed or expanded by interaction with its surroundings.
aerobiology
aerography
The production of weather charts.
aeronomy
The branch of meteorology that studies the upper regions of the Earth's or other planetary atmospheres, specifically their atmospheric motions, chemical compositions and properties, and interactions with the other parts of the atmosphere and with space.
aerosol
A suspension of fine solid particles or liquid droplets in air or another gas. Examples of natural aerosols include mist, clouds, fog, and dust.
ageostrophy
air mass
A volume of air defined by its temperature and content of water vapor.
air-mass thunderstorm
air parcel
In fluid dynamics, any amount of air that remains identifiable throughout its dynamic history while moving with an associated air flow.
Alberta clipper
almanac
An annual publication of calendar events.
altocumulus castellanus
altocumulus
altostratus
American Meteorological Society (AMS)
anabatic wind
anemometer
A scientific instrument used to measure wind speed.
annular tropical cyclone
anticyclone
anticyclonic rotation
anticyclogenesis
arcus cloud
Arctic cyclone
Atlantic hurricane
atmosphere
The various layers of gases surrounding the Earth and held in place by gravity. The Earth's atmosphere is the origin of the weather phenomena studied in meteorology. Atmospheric composition, temperature, and pressure vary across a series of distinct sublayers including the troposphere and stratosphere.
atmospheric circulation
atmospheric convection
atmospheric density
atmospheric pressure
atmospheric sciences

Sometimes called aerology.

The collective of scientific disciplines that studies the Earth's atmosphere and its processes, including the effects other systems have on the atmosphere and those the atmosphere has on other systems. Meteorology and climatology are sub-disciplines.
atmospheric sounding
A measurement of the vertical distribution of physical properties through an atmospheric column, usually including pressure, temperature, wind speed and direction, moisture content, ozone concentration, and pollution, among others.
atmospheric tide
autumn
avalanche
Aviation Area Forecast (FA or ARFOR)

Also simply called an area forecast.

A former message product of the U.S. National Weather Service issued to provide information to pilots and aviation routes about weather conditions across a large regional area within the United States. FAs were issued three times daily, valid for 18 hours and covered an area the size of several states. They were replaced by Graphic Area Forecasts (GFAs) in 2017.

## B

backscatter
The diffuse reflection of waves, particles, or signals back to the same direction from which they originated. Backscattering is the principle underlying all weather radar systems, which can distinguish radar returns backscattered from target aerosols such as raindrops and snowflakes because the strength of the returns depends largely on the size and reflectivity of the targets.
ball lightning
barbs
barograph
A scientific instrument used to measure and record changes in atmospheric pressure over time.
baroclinity

Also called baroclinicity.

barotropity

Also called barotropicity.

barometer
A scientific instrument used to measure atmospheric pressure.
Beaufort scale
Bernoulli's principle
Bishop's ring
black ice
blizzard
A severe snowstorm characterized by strong sustained winds of at least 35 mph (56 km/h) and typically lasting three hours or more. They can have an immense size, covering hundreds or thousands of square miles, and occur most often in temperate, polar, or mountainous regions during the winter.
blowing dust or sand
blowing snow
bounded weak echo region (BWER)
bow echo
A characteristic radar return from a mesoscale convective system that is shaped like an archer's bow and usually associated with squall lines or lines of convective thunderstorms. The distinct bow shape is a result of the focusing of a strong flow at the rear of the system. Especially strong bow echoes may develop into derechos.
breeze
brightband
Bulk Richardson Number (BRN)
A dimensionless ratio related to the consumption of turbulence divided by the shear production of turbulence (the generation of kinetic energy caused by wind shear). It is an approximation of the Gradient Richardson Number.
buoyancy
bushfire

## C

Canadian Meteorological and Oceanographic Society (CMOS)
The national society of individuals and organizations dedicated to advancing atmospheric and oceanic sciences and related environmental disciplines in Canada, officially constituted in 1967.
capping inversion
castellanus

Also called castellatus.

A cloud species that displays at least in its upper part cumuliform protuberances resembling the turrets of a castle, giving a crenellated aspect.
ceiling
ceiling balloon
ceiling projector
ceilometer
Center for Analysis and Prediction of Storms (CAPS)
chinook wind
cirrocumulus
cirrostratus
cirrus
clear ice
A type of solid precipitation which forms when relatively large drops of water are supercooled into a dense, transparent coating of ice without air or other impurities. It is similar to glaze and hard rime and, when formed on the ground, is often called black ice.
clear-air turbulence
climate
The statistics of weather in a given region over long periods of time, measured by assessing long-term patterns of variation in temperature, atmospheric pressure, humidity, wind, precipitation, and other meteorological variables. The climate of a particular location is generated by the interactions of the atmosphere, hydrosphere, cryosphere, lithosphere, and biosphere and strongly influenced by latitude, altitude, and local topography. Climates are often classified according to the averages or typical ranges of different variables, most commonly temperature and precipitation.
climatology

Also called climate science.

A branch of the atmospheric sciences that studies climate, defined as weather conditions averaged over an extended to indefinite period of time. Climatology incorporates aspects of oceanography, geology, biogeochemistry, and the related field of meteorology to understand the long-term dynamics of climate-influencing phenomena and to produce climate models which can be used to estimate past climates and predict future climates.
cloud
An aerosol consisting of a visible mass of minute liquid droplets, frozen crystals or other particles suspended in the atmosphere. Water or various other chemicals may compose the droplets and crystals. On Earth, clouds are formed as a result of the saturation of an air mass when it is cooled to its dew point or when it gains sufficient moisture (usually in the form of water vapor) from an adjacent source to raise the dew point to the ambient temperature. There are many different types of clouds, which are classified and named according to their shape and altitude.
cloud atlas
cloud base
The lowest altitude of the visible portion of a cloud.
cloud iridescence

Also called irisation.

cloud species
Any of a set of 14 Latin terms used to describe the shape and internal structure of tropospheric clouds. Cloud species are subdivisions of cloud genera and are themselves further subdivided into cloud varieties.
cloud tag
cloud type

Also called a cloud genus.

Any of a set of Latin names used to classify and identify clouds occurring in the troposphere, typically by characteristics such as their altitude, shape, and convective activity. A set of 10 or 12 traditional cloud types defined by the World Meteorological Organization and further subdivided into cloud species and cloud varieties is widely used in meteorology. Other classification systems have proposed many additional types.
cloudburst
coastal flooding
col

Also called a saddle point or neutral point.

The point of intersection of a trough and a ridge in the pressure pattern of a weather map. It generally takes the shape of a saddle in which the air pressure is slightly higher than that within the low-pressure regions but still lower than that within the anticyclonic zones.
cold front
cold wave

Also called a cold spell or cold snap.

cold-core low
A type of low-pressure area that forms in southeastern Colorado or northeastern New Mexico, in the United States, and then proceeds to move east across the Great Plains, often producing heavy snow and ice when occurring in the winter.
convection
See atmospheric convection.
convective available potential energy (CAPE)
convective condensation level
convective inhibition (CIN)
convective instability
convective outlooks
convective storm detection
convergence
convergence zone
corona
crepuscular rays
crosswind
Crow instability

Also called the vortex Crow instability.

An inviscid line-vortex instability most commonly observed in the skies behind large aircraft such as the Boeing 747. It occurs when the wingtip vortices interact with contrails from the engines, producing characteristic visual distortions in the shapes of the contrails.
cumulonimbus
cumulus
cumulus congestus
cumulus humilis
cumulus mediocris
cyclone
Any large-scale air mass characterized by inward spiraling winds which rotate around a strong center of low atmospheric pressure. Cyclones can form over land or water, can vary in size from mesocyclones such as tornadoes to synoptic-scale phenomena such as tropical cyclones and polar vortices, and may transition between tropical, subtropical, and extratropical phases.
cyclonic rotation
cyclogenesis
The development or strengthening of a cyclonic circulation in the atmosphere. Cyclogenesis may refer to a number of different processes that occur under a variety of conditions and at a variety of scales, all of which result in the formation of some sort of cyclone; for instance, tornadoes are a type of mesocyclone whose development may be variously described as cyclogenesis or, more specifically, tornadogenesis. Contrast anticyclogenesis.

## D

A type of specialized eyewear used by meteorologists and astronomers for adapting the eyes to the dark prior to an observation made at night, or for aiding with identification of clouds during bright sunshine or when there is a glare from snow.
dawn
daytime
The period of the day between sunrise and sunset, during which any given point on the Earth experiences natural illumination from especially direct sunlight, known as daylight.
dBZ
debris cloud
deformation
The rate of change of shape of a fluid body such as an air mass. This quantity is very important in the formation of atmospheric fronts, in the explanation of cloud shapes and in the diffusion of materials and properties through the atmosphere.
dense fog
depression
See low-pressure area.
derecho
detention basin
detention dam
dew
dew point
(Td)
dew point depression
Diablo wind
diamond dust
divergence
diffluence
disdrometer
A scientific instrument used to measure the size distribution and velocity of falling hydrometeors such as raindrops.
diurnal temperature variation
Dobson unit
doldrums
Doppler on Wheels (DOW)
downburst
A surface-level wind system that emanates from an elevated point source and blows radially in all directions upon making contact with the ground. Downbursts are created when areas of significantly rain-cooled air descend rapidly, and can produce very strong damaging winds. They are often confused with tornadoes, though a tornado causes air to move inward and upward whereas a downburst directs it downward and outward. Microbursts, macrobursts, and heat bursts are all types of downburst.
downdraft
drifting snow
drizzle
drought

Also called a drouth.

Any prolonged period of below-average precipitation in a given region that results in shortages in the local water supply, whether of atmospheric, surface water, or ground water. Droughts can last for months or even years, and may be declared after as few as 15 days; annual or seasonal decreases in precipitation, such as dry seasons in the tropics, are sometimes called droughts, though a true drought is by definition abnormal or irregular. Drought conditions result from the confluence of a wide variety of climatic factors and may be exacerbated by hot temperatures; in turn, droughts may increase the likelihood of wildfires.
dry lightning
Lightning associated with a dry thunderstorm.
dry line
dry microburst
dry punch
dry season
dry thunderstorm

Also called a heat storm.

A thunderstorm that produces thunder and lightning but in which most or all of its precipitation evaporates before reaching the ground. Dry thunderstorms occur necessarily in dry conditions, and their lightning strikes, sometimes referred to as dry lightning, are a major cause of wildfires.
DSD
dusk
dust devil
dust storm

## E

eddy
Ekman layer
The layer in a fluid in which there is a force balance between the pressure-gradient force, the Coriolis force, and turbulent drag. Ekman layers occur in both the atmosphere and the ocean.
Ekman number
Ekman spiral
Ekman transport
energy-helicity index (EHI)
El Niño
El Niño–Southern Oscillation
emagram
One of four thermodynamic diagrams used to display temperature lapse rate and moisture content profiles in the atmosphere. Emagrams have axes of temperature (T) and pressure (p). Temperature and dew point data from radiosondes are plotted on these diagrams to allow calculations of convective stability or convective available potential energy.
Enhanced Fujita scale (EF scale)
entrainment
Environmental Modeling Center (EMC)
Environmental Research Laboratories (ERL)
The predecessor agency (1965–1970) to the National Oceanic and Atmospheric Administration (1970–present).
equivalent temperature (${\displaystyle T_{e}}$)
equivalent potential temperature (${\displaystyle \theta _{e}}$)
Eulerian equations
European windstorm
explosive cyclogenesis
extratropical cyclone
extreme weather
Any weather that is unexpected, unusual, unpredictable, unseasonal, or especially severe (i.e. weather at the extremes of an historical distribution).
eye

## F

fall wind
See katabatic wind.
Fata Morgana
fetch

Also called fetch length.

The length of water over which a given wind blows. Fetch length and wind speed together determine the size of the waves that form on the surface of a body of water; the longer the fetch and the stronger the wind, the more wind energy is imparted to the water surface and the larger the resulting sea state.
field mill
fire whirl
firestorm
flash flood
Any flood which very rapidly inundates low-lying areas such as washes, rivers, dry lakes, and basins, especially one which recedes again in less than six hours. Flash flooding can be caused by heavy rain associated with severe weather, large amounts of meltwater from melting ice or snow, or the sudden collapse of a natural ice or debris dam.
flash freezing
flood
An overflow of water which submerges land that is usually dry. Flooding may occur when water bodies such as rivers, lakes, or oceans escape their boundaries by overtopping or puncturing levees, or it may occur when precipitation accumulates on saturated ground more rapidly than it can either infiltrate or run off.
flumen

Also called a beaver's tail.

fog
A visible aerosol of minute water droplets or ice crystals that is suspended in the air at or near the Earth's surface. Fog is often considered a type of low-lying cloud and is heavily influenced by local topography, nearby bodies of water, and wind conditions.
fogbow
föhn wind

Also spelled foehn wind.

A type of warm, dry, downslope wind that occurs in the lee of a mountain range.
forward-flank downdraft (FFD)

Also called a front-flank downdraft.

fractus (Fr)

Often used interchangeably with scud.

frazil ice
freezing drizzle
freezing fog
freshet
freezing rain
front
A boundary separating two masses of air of different densities and usually also of different temperatures and humidities. Weather fronts are the principal cause of meteorological phenomena outside the tropics, often bringing with them clouds, precipitation, and changes in wind speed and direction as they move. Types of fronts include cold fronts, warm fronts, and occluded fronts.
frontogenesis
frontolysis
frost
Fujita scale (F scale)
funnel cloud

## G

gale
A strong surface wind, typically used as a descriptor in nautical contexts. Gales are variously defined based on their speed; in the modern Beaufort scale, sustained winds of 28–33 kn (52–61 km/h; 32–38 mph), Beaufort number 7, are designated as near gales and those of 34–47 kn (63–87 km/h; 39–54 mph), spanning Beaufort numbers 8 and 9, as gales.
gale warning
gap wind
geopotential height
geostrophic wind
The theoretical wind that would result from an exact balance between the Coriolis force and the pressure gradient force (known as geostrophic balance). The true wind almost always differs from the geostrophic wind due to the influence of other forces such as friction from the ground.
glaze
GPS meteorology
graupel

Also called soft hail and snow pellets.

A type of precipitation that forms when supercooled water droplets are collected and freeze on falling snowflakes, forming balls of rime 2–5 mm (0.079–0.197 in) in diameter. Graupel is distinct from hail, small hail, and ice pellets.
Great Salt Lake effect
A lake-effect snow in lee of the Great Salt Lake
grease ice
green flash
Greenwich Mean Time (GMT)
ground blizzard
ground truth
Information, such as local weather conditions, provided by direct observation (i.e. empirical evidence) as opposed to information provided by inference.
gust
gust front

## H

haboob
hail
A type of solid precipitation that consists of balls or irregular lumps of ice usually 5–150 mm (0.20–5.91 in) in diameter, each of which is called a hailstone. Hail formation requires environments with strong, upward motion of air and low altitudes at which water freezes, which makes it possible within most thunderstorms. It is distinct from graupel and sleet or ice pellets.
hailstorm
Haines Index

Also called the Lower Atmosphere Severity Index.

A weather index that measures the potential for dry, unstable air to contribute to the development of large or erratic wildland fires. The index derives from data on the stability and moisture content of the lower atmosphere and is calculated over three ranges of atmospheric pressure.
halo
hard rime
Harmattan
haze
hazardous seas warning
hazardous seas watch
heat burst
heat index (HI)

Also called the apparent temperature, felt air temperature, or humiture.

A meteorological index that posits the apparent temperature perceived by the average human being who is exposed to a given combination of air temperature and relative humidity in a shaded area. For example, when the air temperature is 32 °C (90 °F) with 70% relative humidity, the heat index is 41 °C (106 °F).
heat lightning
heat wave
heavy snow warning
A type of weather warning formerly issued by the U.S. National Weather Service to alert areas in which a high rate of snowfall (generally 6 in (15 cm) or more in 12 hours) was occurring or was forecast. The warning was replaced by the Winter Storm Warning for Heavy Snow beginning with the 2008–09 winter storm season.
helicity
high-pressure area
hodograph

Also called a velocity diagram.

A vectorial visual representation of the movement of a body or a fluid, with the position of any data plotted on it proportional to the velocity of the moving particle. In the context of meteorology, hodographs are used to plot winds from atmospheric soundings: for a given vector, wind direction is indicated by the angle from the center axis and wind speed by the distance from the center.
hook echo
horseshoe vortex
humidity
A measure of the amount of water vapor present in a parcel of air. By quantifying the saturation of the air with moisture, humidity indicates the likelihood of precipitation, dew, or fog occurring. The amount of water vapor needed to achieve full saturation increases as the air temperature increases. Three primary measurements of humidity are widely employed in meteorology: absolute, relative, and specific.
humidex
humilis
hurricane
The local name for a tropical cyclone that occurs in the Atlantic Ocean or northeastern Pacific Ocean.
hurricane hunters
huayco
hydrometeor
Any particulate of liquid or solid water within the atmosphere, encompassing all types of precipitation, formations due to condensation such as clouds and haze, and particles blown from the Earth's surface by wind such as blowing snow and sea spray.
hydrometeorology
hydrosphere
The combined mass of all solid, liquid, and gaseous forms of water found on, beneath, or above the surface of the Earth, including all oceans, lakes, streams, groundwater, atmospheric water vapor, snow, ice caps, and glaciers.
hydrostatic equilibrium
hygrometer
A scientific instrument used to measure humidity.
hypsometer
hygroscopy

## I

ice
Water frozen into a solid state. Ice is abundant on Earth's surface and in the atmosphere and plays a major role in Earth's water cycle and climate. Its natural occurrence in weather phenomena takes many forms, including snowflakes, hail, frost, icicles and ice spikes.
iceberg
ice accretion indicator
ice crystals
ice fog
ice pellets
ice spike
ice storm
icicle
A long, slender spike of ice formed when water dripping or falling from an object freezes.
ideal gas law
in situ
incus
Indian summer
inflow
instrument flight rules (IFR)
International Standard Atmosphere
irisation
See cloud iridescence.

## J

jet stream
A narrow, fast-flowing, meandering air current primarily occurring in the upper part of the troposphere, at altitudes above 9 km (30,000 ft), and usually flowing from west to east. The Northern and Southern Hemispheres each have a polar jet and a subtropical jet; low-level jets and other types of jet streams can form under certain conditions.

## K

K-index
${\displaystyle K_{DP}}$
katabatic wind

Also called a drainage wind or fall wind, or spelled catabatic wind.

A wind that carries high-density air from a higher elevation down a slope under the force of gravity, usually at speeds of the order of 10 kn (19 km/h) or less but occasionally at much higher speeds.
Kelvin temperature scale
Kelvin–Helmholtz instability
khamsin
kinematics
A branch of classical mechanics that describes the motion of points, bodies, and systems of bodies without considering the forces that caused the motion.
Köppen climate classification

## L

${\displaystyle L_{DR}}$
Lagrangian equations
La Niña
lake-effect snow
A weather phenomenon produced when a cold air mass moves across long expanses of warmer lake water, which causes the lowest layers of air to pick up warm water vapor from the lake, rise through the upper layers, freeze and then precipitate on the lake's leeward shores. In combination with orographic lift, the effect produces narrow but very intense bands of precipitation, especially snow, which can deposit at very high rates and result in very large amounts of snowfall over a region. The same effect can also occur over bodies of salt water, when it is termed ocean-effect or bay-effect snow.
land breeze
landfall
landslide
landspout
A type of tornado emerging from a parent cloud that does not contain a pre-existing mid-level mesocyclone or other rotation. Landspouts share a development process and resemblance with waterspouts. They are generally smaller and weaker than supercell tornadoes and are rarely detected by Doppler weather radar.
lapse rate
lee trough
lee wave
Lemon technique
A method used by meteorologists which focuses on updrafts and uses weather radar to determine the relative strength of thunderstorm cells in a vertically sheared environment.
lenticular cloud
level of free convection (LFC)
Lidar

Also rendered as LIDAR, LiDAR, or LADAR.

A surveying method that measures the distance to a target by illuminating the target with pulsed laser light and measuring the reflected pulses with a sensor; differences in laser return times and wavelengths can then be used to create digital three-dimensional representations of the target. The name is now used as an acronym of light detection and ranging.
lifted condensation level (LCL)
lifted index (LI)
light pillar
lightning
lightning activity level
lightning detection
lightning strike
line echo wave pattern (LEWP)
low-level jet
low-pressure area (L)
low-topped supercell (LT)
lysimeter

## M

MAFOR
A North American system used in the transmission of marine weather forecasts to compress large amounts of information about meteorological and marine conditions, including visibility, expected future wind speed and direction, the "state of sea", and the period of validity of the forecast, into shorter code for convenience during radio broadcasting. MAFOR is an abbreviation of MArine FORecast.
marine cloud brightening
marine stratocumulus
mass flow
The movement of a fluid, such as an air mass, down a pressure or temperature gradient.
mesocyclone
mesohigh
mesolow
mesonet
mesoscale convective complex (MCC)
mesoscale convective discussion (MCD)
mesoscale convective system (MCS)
mesoscale convective vortex (MCV)
mesoscale meteorology
mesosphere
mesovortices
METAR
Météo-France
meteorology
A branch of the atmospheric sciences which seeks to understand and explain observable weather events, with a major focus on weather prediction. Meteorology uses variables familiar in atmospheric chemistry and atmospheric physics to describe and quantify meteorological phenomena, including temperature, pressure, water vapor, mass flow and how these properties interact and change over time.
microburst
micronet
A weather observation network even denser than a mesonet, such as the Oklahoma City Micronet.
microscale meteorology
mini-supercell
A distinct kind of supercell that is smaller than a typical supercell.
A fallacious term often used in news media to refer to damaging winds accompanying a thunderstorm, indifferently caused by tornadoes or microburst, on a small area.
misocyclone

Also called a landspout.

misoscale meteorology
mixing ratio
Modified Fujita Scale
An update to the original Fujita scale from 1971 proposed by Ted Fujita in 1992.
moisture convergence
An area where moisture concentrates due to the air flow near the surface.
mountain breeze
mountain-gap wind
multicellular thunderstorm
moisture

Also called moisture content or water content.

The presence of liquid, especially water, within a body or substance, often in trace amounts. Moisture in the air in the form of water vapor underlies the concept of humidity.
monsoon
Morning Glory cloud
mudflow
mudslide

## N

National Center for Atmospheric Research (NCAR)
National Centers for Environmental Prediction (NCEP)
National Hurricane Center (NHC)
National Oceanic and Atmospheric Administration (NOAA)
National Severe Storms Forecast Center (NSSFC)
A predecessor forecasting center to the Storm Prediction Center that was located in Kansas City, Missouri.
National Severe Storms Laboratory (NSSL)
A NOAA lab in Norman, Oklahoma tasked with researching severe weather.
The official NOAA record of all known tornadoes within the United States from 1950 to present.
National Weather Center (NWC)
National Weather Service (NWS)
National Weather Service Training Center (NWSTC)
needle ice
negative tilt
nephelometer
nephoscope
A scientific instrument used to measure the altitude, direction, and velocity of atmospheric clouds.
nimbostratus
noctilucent cloud
nor'easter

Also called a northeaster.

A macro-scale extratropical cyclone, especially one which impacts the middle and north Atlantic coasts of North America. The name derives from the direction of the winds that most strongly affect the eastern seaboard between the months of October and March. Such storms are often accompanied by very heavy rain or snow, which can cause severe coastal flooding, and hurricane-force winds.
nor'west arch

Associated with nor'wester.

a variety of föhn cloud found in the South Island of New Zealand when north-westerly winds push cooling moist air over the spine of the Southern Alps mountain range.
Novaya Zemlya effect
nowcasting
numerical weather prediction

## O

occluded front
okta

Also spelled octa.

A unit of measurement used to describe the amount of cloud cover at a given location in terms of how many eighths of the sky are covered in clouds, ranging from 0 oktas (completely clear) to 8 (completely overcast) or sometimes 9 oktas (indicating that the sky is obstructed from view).
omega equation
opacity
orographic cloud
orographic precipitation
overcast
The condition of cloud clover wherein clouds obscure at least 95% of the sky. The type of cloud cover that qualifies as overcast is distinguished from obscuring surface-level phenomena such as fog.
overshooting top
OU-PRIME
outflow
outflow boundary
outflow jet
ozone depletion
ozone layer

## P

paleoclimatology
pan evaporation
pancake ice
A form of ice that consists of round, flat pieces of ice with elevated rims, diameters ranging from 30 cm (12 in) to 3 m (9.8 ft), and thicknesses of up to 10 cm (3.9 in).
pannus

Also called scud; often used interchangeably with fractus.

pampero
parhelia
See sun dog.
partial pressure
Particularly Dangerous Situation
pascal (Pa)
The SI derived unit of pressure, defined as one newton per square metre. In meteorology, measurements of atmospheric pressure are often given in kilopascals (kPa).
Pascal's law
Pearson scale

Also called the Fujita-Pearson scale or F-P-P scale.

A tornado rating scale developed by Allen Pearson differentiating path length (P) and path width (P) to accompany NOAA Fujita scale (F) ratings.
permafrost
photometeor
Any bright object or other optical phenomenon appearing in the Earth's atmosphere when sunlight or moonlight creates a reflection, refraction, diffraction, or interference under particular circumstances. Common examples of photometeors include halos, rainbows, coronas, crepuscular rays, and sun dogs.
Phi_DP (${\displaystyle \Phi _{DP}}$)
pileus
pilot balloon
pilot report (PIREP)
polar low
polar mesospheric clouds
polar stratospheric cloud
polar vortex
Either of the two very large, persistent, rotating, upper-level low-pressure areas suspended in the Earth's atmosphere near the geographic poles. The polar vortices predictably strengthen during their local winter and weaken during their local summer as the temperature contrast between the poles and the Equator changes. When either vortex is weak, high-pressure zones of lower latitudes may push poleward, driving the vortex, jet stream, and masses of cold, dry polar air into the mid-latitudes, which can cause sudden, dramatic drops in temperature known as cold waves.
potential temperature (${\displaystyle \theta }$)
potential vorticity
power flash
A sudden bright light caused when an overhead power line is severed or especially when a transformer explodes. Severe weather is one of the most common causes.
precipitable water
pressure system
precipitation
Any product of the condensation of atmospheric water vapor that falls by gravity, the main forms of which include rain, sleet, snow, hail, and graupel. Precipitation occurs when a portion of the atmosphere becomes locally saturated with water vapor such that the water condenses into liquid or solid droplets and thus "precipitates" out of the atmosphere.
precipitation types
prevailing winds
psychrometer
psychrometrics
pulse storm
pyranometer
A type of actinometer used to measure solar irradiance on a planar surface and solar flux density in the hemisphere above.
pyrgeometer
pyrheliometer

## Q

Q-vector
quantitative precipitation estimation (QPE)
A method of estimating the approximate amount of precipitation that has fallen at a location or across a region.
quantitative precipitation forecast (QPF)
The expected amount of melted precipitation accumulated over a specified time period within a specified area.
quasi-geostrophic equations
quasi-linear convective system (QLCS)
quasistatic approximation

## R

A battery-powered scientific instrument released into the atmosphere, usually by a weather balloon, which measures various atmospheric parameters and transmits them by radio telemetry to a ground receiver. Radiosondes are essential sources of meteorological data, and hundreds are launched all over the world everyday.
rain
A type of precipitation that occurs when liquid water in the form of droplets condenses from atmospheric water vapor, becoming heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth.
rainbow
raindrop size distribution
rain and snow mixed
rain gauge
rain of animals
rain showers

Often simply called showers.

Short, intense periods of rainfall, especially when occurring in widely scattered locations.
Rankine vortex
rapid intensification
rear flank downdraft (RFD)
relative humidity
remote sensing
The acquisition of information about an object or phenomenon without making physical contact with the object and thus in contrast to on-site observation. In meteorology, satellite- or aircraft-based sensor technologies are widely used to detect and classify objects on the surface or within the atmosphere or oceans based on propagated electromagnetic signals.
Rho_hv (${\displaystyle \rho _{hv}}$)
ridge
rime
A coating of ice on the surface of an object. See hard rime and soft rime.
rogue wave
roll cloud
Rossby number
Rossby wave
rotation
See cyclonic rotation.

## S

sandstorm
See dust storm.
sastrugi

(sing.) sastruga; also spelled zastrugi

Sharp, irregular grooves or ridges formed on a snow surface by wind erosion, saltation of snow particles, and deposition, usually parallel to the prevailing winds. They are often found in the polar regions and in large, open areas such as frozen lakes in cold temperate regions.
scud
See pannus.
sea breeze
sea spray
sea state
season
Any division of the year marked by changes in weather, ecology and the duration of daylight. Seasons result from the Earth's orbit around the Sun and its axial tilt relative to the ecliptic plane. In temperate and polar regions, four calendar-based seasons – spring, summer, autumn and winter – are generally marked by significant changes in the intensity of sunlight that reaches the Earth's surface; these changes become less dramatic as one approaches the Equator, and so many tropical regions have only two or three seasons, such as a wet season and a dry season. In certain parts of the world, the term is also used to capture the timing of important ecological events, such as hurricane seasons, flood seasons and wildfire seasons.
severe thunderstorm
severe weather
Any dangerous meteorological phenomena with the potential to cause damage on the ground surface, serious social disruption, or loss of human life. There are many types of severe weather, including strong winds, excessive precipitation, thunderstorms, tornadoes, tropical cyclones, blizzards, and wildfires. Some severe weather may be more or less typical of a given region during a given season; other phenomena may be atypical or unpredictable.
shelf cloud
shortwave trough
SIGMET
simoom
single cell thunderstorm
sirocco
skew-T log-P diagram
Skywarn

Sometimes stylized as SKYWARN.

The storm-spotting program of the U.S. National Weather Service. Skywarn organizations have also been formed in Europe and Canada.
sleet
slush
snow
A type of solid precipitation in the form of ice crystals which precipitate from the atmosphere and subsequently undergo changes on the Earth's surface. Snow occurs when snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets, which freeze in hexagonal-shaped crystals; upon reaching the ground it may then accumulate into snowpack or snowdrifts and, over time, metamorphose by sintering, sublimation, and freeze-thaw mechanisms. Unless the local climate is cold enough to maintain persistent snow cover on the ground, snow typically melts seasonally.
snow gauge
snow grains
snow roller
snowbelt
snowdrift
snowflake
snowsquall
snowstorm

Often used interchangeably with winter storm.

A type of winter storm accompanied particularly by heavy precipitation in the form of snow. Very large snowstorms with strong winds and meeting certain other criteria are called blizzards.
SODAR
solarimeter
sounding
See atmospheric sounding.
sounding rocket
specific humidity
spindrift

Also called spoondrift.

Sea spray blown from cresting waves during a gale. This spray "drifts" in the direction of the gale and is distinct enough that it is sometimes used to judge wind speed at sea.
spring
sprite
squall line
St. Elmo's fire
standard atmosphere
station model
stationary front
steam devil
Stevenson screen
storm
Any disturbed state of an environment or atmosphere especially affecting the ground surface and strongly implying severe weather. Storms are characterized by significant disruptions to normal atmospheric conditions, which can result in strong wind, heavy precipitation, thunder and lightning (as with a thunderstorm), among other phenomena. They are created when a center of low pressure develops within a system of high pressure surrounding it.
storm cell
An air mass which contains up and down drafts in convective loops and which moves and reacts as a single entity. It functions as the smallest unit of a storm-producing weather system.
storm chasing
Storm Data and Unusual Weather Phenomena (SD)

Also simply abbreviated to Storm Data.

A National Climatic Data Center (NCDC) publication beginning in 1959 which details quality-controlled tornado and other severe weather summaries as the official NOAA record of such events.
storm shelter
storm spotting
storm surge
Storm Prediction Center (SPC)
Storm Track
straight-line wind

Also called a plough wind, thundergust, or hurricane of the prairie.

Any very strong and potentially damaging wind that lacks the rotational damage pattern associated with the winds of a tornado and hence is said to blow in a "straight line". Straight-line winds commonly accompany the gust front of a thunderstorm or originate with a downburst and may gust as high as 130 mph (210 km/h).
stratocumulus
stratosphere
stratus
summer
Stüve diagram
sun dog
sunshine recorder
sunshower
A meteorological phenomenon in which rain falls while the sun is shining.
supercell
subtropical cyclone
surface weather analysis
surface weather observation
sustained wind
synoptic scale meteorology

## T

tail cloud

Also called a cauda.

A ragged band of cloud and/or fractus extending from a wall cloud toward the precipitation core.
temperature
A physical quantity expressing the thermal motion of a substance, such as a mass of air in the atmosphere, and proportional to the average kinetic energy of the random microscopic motions of the substance's constituent particles. Temperature is measured with a thermometer calibrated in one or more temperature scales: the Kelvin scale is the standard used in scientific contexts, but the Celsius and Fahrenheit scales are more commonly used in everyday contexts and for weather forecasting.
temperature inversion
tephigram
terminal aerodrome forecast (TAF)
thermal

Also called a thermal column.

A column of rising air in the lower altitudes of the Earth's atmosphere. It is a form of atmospheric updraft created by the uneven heating of the Earth's surface by solar radiation, and an example of atmospheric convection.
thermal wind
thermo-hygrograph
thermodynamics
thermodynamic diagrams
thermometer
An instrument used to measure temperature or a temperature gradient.
thermosphere
thunder
thundershower
A relatively weak thunderstorm.
thundersnow
thunderstorm

Also called an electrical storm or lightning storm.

A storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Thunderstorms result from the rapid upward movement of warm, moist air, often along a front. They can develop in any geographic location but are most common in the mid-latitudes. They are usually accompanied by strong winds and heavy rain; especially strong or severe thunderstorms can produce some of the most dangerous weather phenomena, including large hail, downbursts, and tornadoes.
thunderstorm asthma
tilted updraft

Also called a twister, whirlwind, or cyclone.

A rapidly rotating column of air that is in contact with both a parent cloud and the surface of the Earth. Tornadoes come in many shapes and sizes, and they are often visible in the form of a condensed funnel originating from the base of a cumulonimbus cloud, usually during a thunderstorm, with a cloud of rotating dust and debris beneath it. The most extreme tornadoes can achieve wind speeds of more than 300 mph (480 km/h), span more than 2 mi (3.2 km) in diameter, and stay on the ground for dozens of miles (more than 100 km) before dissipating.
Tornado and Storm Research Organisation (TORRO)
TORRO scale
training
tropical cyclone

Variously called a hurricane, typhoon, tropical storm, cyclonic storm, or simply cyclone.

A very large, rapidly rotating storm system characterized by a low-pressure center surrounded by a closed low-level atmospheric circulation, strong winds, and continuous spiral bands of thunderstorms that produce heavy rain. Tropical cyclones develop almost exclusively over and derive their strength from warm tropical seas. The strongest systems can last for more than a week, span more than 1,000 mi (1,600 km) in diameter, and cause significant damage to coastal regions with powerful winds, storm surges, and concentrated precipitation that leads to flooding. Depending on its location and strength, a tropical cyclone may be referred to by different names and categorized within a variety of classes.
tropical cyclone scales
tropical cyclogenesis
tropical depression
tropical disturbance
tropical storm
tropical wave
tropics
tropopause
troposphere
The lowest layer of the Earth's atmosphere, within which nearly all weather phenomena occur. The troposphere contains approximately 75% of the atmosphere's total mass and 99% of its water vapor and aerosols. The average height of the troposphere above the Earth's surface varies between 6 and 18 km (3.7 and 11.2 mi) depending on latitude.
trough
trowal
tsunami
turbulence
twilight
1.  The indirect illumination of the lower atmosphere caused by the scattering of sunlight when the Sun itself is not directly visible because it is below the horizon.
2.  The time period during which such illumination occurs, either between astronomical dawn and sunrise or between sunset and astronomical dusk.
TWISTEX
An acronym for Tactical Weather-Instrumented Sampling in/near Tornadoes EXperiment.
typhoon
The local name for a tropical cyclone that occurs in the northwestern Pacific Ocean, between 180° and 100°E in the Northern Hemisphere.

## U

unstable airmass
updraft

Also called a vertical draft.

upper-air chart
upper-air sounding
upper-air trough
upper-level low
upper-level outflow
upslope fog
urban heat island
US Standard Atmosphere
University Corporation for Atmospheric Research (UCAR)
UTC

## V

valley breeze
valley exit jet
vertical draft
See updraft.
vertically integrated liquid (VIL)
vertical wind shear
virga
virtual temperature
visibility
visual flight rules (VFR)
A set of regulations under which a pilot operates an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going, as opposed to instrument flight rules, under which operation of the aircraft primarily occurs through referencing the onboard instruments rather than through visual reference to the ground and environs.
Von Kármán constant
Von Kármán vortex street
Von Kármán wind turbulence model
vortex

(pl.) vortices or vortexes

A region within a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices are a major component of turbulence and may be observed in many types of meteorological phenomena, including the winds surrounding a tropical cyclone, tornado or dust devil.
vorticity

## W

wall cloud

Also called murus or a pedestal cloud.

A large, localized, persistent, and often abrupt lowering of cloud that develops beneath the surrounding base of a cumulonimbus cloud and from which tornadoes sometimes form.
warm front
Warning Decision Training Branch (WDTB)
water vapor
Water in its gaseous state. Water vapor is ubiquitous in the atmosphere, being continuously generated by evaporation and removed by condensation, and plays a major role in numerous meteorological processes.
waterspout
weak echo region (WER)
weather
The state of the atmosphere at a given time and location. Weather is driven by a diverse set of naturally occurring phenomena, especially air pressure, temperature, and moisture differences between one place and another, most of which occur in the troposphere.
weather balloon
weather bomb
weather forecasting
The application of science and technology to predict the conditions of the atmosphere at a given time and location. Weather forecasts are made by collecting quantitative data about the current state of the atmosphere at a given place and then using meteorology to project how the atmosphere will change. Forecasting is important to a wide variety of human activities, including business, agriculture, transportation, recreation and general health and safety, because it can be used to protect life and property.
weather front
See front.
weather map
A map which displays various meteorological features across a particular area for a particular point or range of time. Weather maps often use symbols such as station models to conveniently present complicated meteorological data. They are used for both research and weather forecasting purposes.
weather modification
Weather Prediction Center (WPC)
1.  In the United States, WSR-1, WSR-57, WSR-74, and WSR-88D.
weather reconnaissance
weather satellite
weather spotting
The act of observing weather, often on the ground, for the purpose of reporting to a larger group or organization, such as the U.S. National Weather Service.
weather station
weather vane
Weatherwise
A photographically adorned general interest weather magazine that frequently publishes articles on tornadoes and other severe weather.
wet-bulb temperature
wet-bulb globe temperature
wet season
whirlwind
wildfire
willy-willy
See dust devil.
wind
The bulk movement of air within the Earth's atmosphere. Wind occurs on a wide range of scales, from very strong thunderstorm flows lasting tens of minutes to milder local breezes lasting a few hours to global atmospheric circulations caused by the differential heating of the Equator and the poles and the Earth's rotation. Winds are often referred to by their strength and direction; the many types of wind are classified according to their spatial scale, their speed, the types of forces that cause them, the regions in which they occur, and their effects.
wind chill
wind direction
The direction from which a wind originates; e.g. a northerly wind blows from the north to the south. Wind direction is usually reported using cardinal directions or in azimuth degrees measured clockwise from due north. Instruments such as windsocks, weather vanes, and anemometers are commonly used to indicate wind direction.
wind gust
wind profiler
wind shear

Sometimes used interchangeably with wind gradient.

Any difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal.
wind speed
windstorm
windsock
winter
winter storm

Often used interchangeably with snowstorm.

1.  Any storm which occurs during the local winter.
2.  Any meteorological event in which varieties of precipitation which can only occur at low temperatures are formed, such as snow, sleet, or freezing rain. Such events are not necessarily restricted to the winter season but may occur in late autumn or early spring, or very rarely in the summer, as well.
winter waterspout

Also called a snowspout.

World Meteorological Organization (WMO)

X band
xerochore

yellow wind
Younger Dryas

## Z

Z-R relation
Zdr
zastrugi
See sastrugi.
zephyr
zonal flow
Zonda wind
zud

Also spelled dzud.