Meteorology is full of technical terms that describe the atmosphere, weather events, and the science behind them. This weather glossary serves as a comprehensive reference for understanding key meteorological concepts, from everyday terms like “humidity” and “forecast” to more complex ideas like “baroclinic instability” and “vorticity.” Whether you’re a student, teacher, amateur forecaster, or simply curious about the weather, this glossary will help you decode the language of meteorology.
Use the alphabetical links below to jump to a specific letter of the glossary. Each term has a clear and concise definition, with examples and context where useful.
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Expand your meteorology knowledge with this comprehensive A–Z Weather Glossary, perfect for students, teachers, and weather enthusiasts. This free PDF resource includes:
- Over 250 clearly defined weather and climate terms
- Accurate definitions with plain-language explanations
- Useful for science classes, storm spotter training, and general reference
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A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | ZA
Absolute Humidity – The total mass of water vapor in a given volume of air, typically expressed in grams per cubic meter (g/m³). Unlike relative humidity, it does not depend on temperature.
Absolute Instability – A condition in the atmosphere where a parcel of air will continue to rise regardless of whether it is saturated or not, because it is always warmer than its surroundings.
Absolute Zero – The lowest possible temperature, 0 K (−273.15 °C or −459.67 °F), where molecular motion theoretically ceases.
Adiabatic Process – A thermodynamic process in which a parcel of air changes temperature without gaining or losing heat to its surroundings. Rising air cools adiabatically; sinking air warms adiabatically.
Advection – The horizontal movement of air or other atmospheric properties such as heat, moisture, or pollutants. Often used in terms like “cold air advection” or “moisture advection.”
Advisory (Weather Advisory) – A notice issued by meteorological services for weather conditions that are potentially hazardous but less severe than a warning.
Air Column – A vertical section of the atmosphere extending upward from a particular location, often used in model predictions.
Air Mass – A large body of air with uniform temperature, humidity, and pressure characteristics. Classified by origin (continental/maritime) and temperature (polar/tropical/arctic).
Air Parcel – A small, hypothetical volume of air used in atmospheric studies, assumed to remain isolated as it rises or sinks.
Air Pressure – The weight of the atmosphere pressing down on the Earth’s surface, measured in millibars (mb) or hectopascals (hPa).
Air Quality Index (AQI) – A measure used to describe the level of air pollution and its potential health effects.
Albedo – The percentage of incoming solar radiation that a surface reflects. Snow has a high albedo, while forests have a low albedo.
Aleutian Low – A semi-permanent low-pressure system located near the Aleutian Islands, influencing winter storm tracks in the North Pacific.
Altimeter – An instrument that measures altitude, often using air pressure. Aircraft and weather balloons rely on altimeters.
Altocumulus – Mid-level clouds that appear as white or gray patches, often forming in groups. May indicate a change in the weather.
Altostratus – Gray or blue-gray clouds covering the entire sky at mid-altitudes. Often precede a warm front and may bring light precipitation.
Anabatic Wind – An upslope wind driven by solar heating of mountain slopes. Opposite of a katabatic wind.
Anemometer – An instrument used to measure wind speed. Types include cup, vane, and sonic anemometers.
Anomaly (Weather Anomaly) – A deviation from the climatological average. For example, a positive temperature anomaly indicates warmer-than-average conditions.
Anticyclone – A weather system with high pressure at the center and winds rotating outward. In the Northern Hemisphere, winds spiral clockwise.
Anticyclonic Flow – Clockwise rotation in the Northern Hemisphere (counterclockwise in the Southern Hemisphere), associated with high pressure.
Apparent Temperature – The perceived temperature, accounting for humidity (heat index) or wind (wind chill).
Arctic Oscillation (AO) – A large-scale mode of climate variability in the Northern Hemisphere, characterized by shifting pressure patterns between the Arctic and mid-latitudes.
Arctic Outbreak – A surge of extremely cold air from the Arctic region into lower latitudes, often associated with high pressure systems.
Atmosphere – The envelope of gases surrounding Earth, divided into layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
Atmospheric River – A narrow corridor of concentrated moisture transport in the atmosphere, often delivering heavy rainfall to coastal regions.
Atmospheric Pressure – The force per unit area exerted by the weight of the air above. Standard sea level pressure is 1013.25 hPa.
Autoconversion – A microphysical process in clouds where small cloud droplets combine to form larger raindrops.
Avalanche – A mass of snow, ice, and debris that rapidly slides down a mountainside, often triggered by weather changes or temperature shifts.
B
Backing Winds – A counterclockwise shift in wind direction over time (in the Northern Hemisphere), typically associated with warm air advection.
Baroclinic Zone – A region where temperature and pressure gradients intersect, often the site of frontal development and storm formation.
Baroclinity – A measure of how much atmospheric density depends on both pressure and temperature, contributing to storm development.
Barograph – A barometer that records pressure readings over time on a rotating drum or digitally.
Barometer – An instrument used to measure atmospheric pressure. Types include mercury, aneroid, and digital.
Barotropic – An atmosphere where surfaces of constant pressure coincide with surfaces of constant temperature. Such a state produces minimal storm activity.
Beaufort Scale – A scale ranging from 0 (calm) to 12 (hurricane) that estimates wind speed based on observed conditions.
Bermuda High – A semi-permanent high-pressure system in the Atlantic Ocean that influences summer weather patterns in North America.
Beta Drift – The movement of a tropical cyclone due to variations in the Coriolis force with latitude, affecting its track.
Black Ice – A thin, nearly invisible layer of ice on roads or sidewalks, especially dangerous for driving and walking.
Blizzard – A severe snowstorm with sustained winds ≥35 mph and visibility <0.25 miles for at least 3 hours.
Blocking Pattern – A persistent atmospheric pattern (such as an Omega block) that prevents normal progression of weather systems.
Blowing Snow – Snow lifted from the ground by strong winds, reducing visibility and often contributing to ground blizzards.
Bomb Cyclone – A rapidly intensifying low-pressure system that undergoes bombogenesis, defined as a pressure drop of ≥24 mb in 24 hours.
Boundary Layer – The lowest part of the atmosphere that interacts directly with Earth’s surface, often affected by friction and heating.
Bow Echo – A radar signature of a thunderstorm line that bows outward, often indicating damaging straight-line winds.
Brine – Saltwater solution used to pre-treat roads ahead of winter storms to prevent ice bonding.
Brightness Temperature – A measure of the radiation intensity from an object, used in satellite meteorology to infer temperature or cloud properties.
Buoyancy – The force that causes air parcels to rise or sink, depending on their temperature and density relative to surrounding air.
Buys Ballot’s Law – In the Northern Hemisphere, if you stand with your back to the wind, low pressure is to your left.
C
Calm – A condition with no measurable wind (0 on the Beaufort scale).
CAPE (Convective Available Potential Energy) – A measure of atmospheric instability that quantifies the energy available for convection. High CAPE values increase the likelihood of strong thunderstorms.
Cap or Capping Inversion – A layer of warm air aloft that prevents air from rising beyond a certain level, suppressing thunderstorm development until it is broken by surface heating or dynamic lifting.
Carbon Dioxide (CO₂) – A greenhouse gas that traps infrared radiation and contributes to global warming. Also naturally present in the atmosphere at around 420 ppm (as of 2025).
Castellanus Clouds – Cumuliform clouds with turret-like tops, indicating mid-level atmospheric instability and potential for later thunderstorm development.
Ceiling – The height of the lowest cloud layer that covers more than half the sky. A critical factor in aviation.
Cell (Storm Cell) – An individual convective unit within a thunderstorm, consisting of an updraft and downdraft. Supercells, multicells, and single cells are key storm types.
Chinook Wind – A warm, dry wind descending the leeward side of mountain ranges, particularly in the western United States and Canada.
Cirrostratus – High-level, thin, ice-crystal clouds covering the sky, often producing a halo around the sun or moon.
Cirrocumulus – High-altitude clouds forming in small, white patches or ripples, composed of ice crystals.
Cirrus Clouds – Wispy, feather-like clouds at high altitudes (20,000–40,000 feet), composed of ice crystals and often signaling changes in the weather.
Clear Air Turbulence (CAT) – Turbulence that occurs in cloudless regions, usually at high altitudes, often associated with jet streams or strong wind shear.
Climate – The long-term average of weather conditions in a region.
Climatology – The scientific study of long-term weather patterns and averages over decades or centuries.
Cloud – A visible mass of condensed water vapor or ice suspended in the atmosphere.
Cloud Base – The lowest altitude of the visible portion of a cloud.
Cloudburst – A sudden, intense rainfall over a localized area, often leading to flash flooding.
Cold Air Damming – A weather phenomenon where cold air is trapped against the east side of a mountain range, influencing precipitation and temperature patterns.
Cold Core Low – A low-pressure system that is colder at the center than its surroundings, common in upper-level lows.
Cold Front – A boundary where a cold air mass replaces a warmer one, typically bringing abrupt weather changes like thunderstorms or a temperature drop.
Columnar Ice Crystals – One of the six basic shapes of ice crystals found in snow, forming at specific temperatures and humidity levels.
Condensation – The process of water vapor turning into liquid water, forming clouds, fog, or dew.
Condensation Nuclei – Tiny particles (dust, salt, smoke) in the atmosphere on which water vapor condenses to form cloud droplets.
Cone of Uncertainty – A graphical forecast used in tropical cyclones to show the probable path of the storm center, expanding over time to account for forecast uncertainty.
Conduction – Heat transfer through direct contact, not usually significant in meteorological processes except near the surface.
Confluence – The horizontal convergence of airflows, often leading to upward motion and cloud development.
Convection – The vertical movement of heat and moisture in the atmosphere, often producing cumulus clouds and thunderstorms.
Convective Inhibition (CIN) – The amount of energy preventing air from rising to the level of free convection. High CIN suppresses storm formation.
Convective Outlook – A forecast from the Storm Prediction Center (SPC) outlining the probability of severe weather over a region for the next 1–3 days.
Convergence – The horizontal inflow of air into a region, causing upward motion and possible cloud formation.
Corona – A colored ring around the sun or moon caused by diffraction of light through water droplets or ice crystals.
Coriolis Effect – The apparent deflection of moving objects (such as wind or ocean currents) caused by Earth’s rotation. Deflection is to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
Crepuscular Rays – Sunbeams that appear to radiate from the sun at dawn or dusk due to scattering by clouds or dust.
Cyclogenesis – The formation or intensification of a low-pressure system (cyclone), often occurring along baroclinic zones or frontal boundaries.
Cyclone – A large-scale air mass that rotates around a low-pressure center. In meteorology, the term includes mid-latitude storms, tropical cyclones, and polar lows.
D
Dam (Decameter) – A unit of measurement equal to 10 meters, used frequently in geopotential height maps (e.g., 500 dam = 5000 meters).
Dew – Water droplets formed by condensation of moisture on surfaces when the temperature drops to the dew point.
Dew Point – The temperature at which air becomes saturated and water vapor condenses into liquid. A key measure of atmospheric moisture.
Dew Point Depression – The difference between the air temperature and the dew point. A small depression indicates high humidity.
Diabatic Process – A process in which heat is added to or removed from an air parcel, such as through radiation or conduction.
Diurnal Cycle – Daily cycle of temperature and weather conditions due to Earth’s rotation and solar heating.
Divergence – The horizontal outflow of air from a region, often associated with descending air and surface high pressure.
Doldrums – A region near the equator with little or no prevailing wind, also known as the Intertropical Convergence Zone (ITCZ).
Doppler Radar – A radar system that detects the motion of precipitation particles and wind by measuring the frequency shift (Doppler effect).
Downdraft – A column of sinking air within a thunderstorm, often bringing heavy precipitation and gusty winds.
Downburst – A strong, localized downdraft from a thunderstorm that spreads out upon hitting the ground, capable of producing damaging straight-line winds.
Drizzle – Light liquid precipitation consisting of very small water droplets, typically with a diameter <0.5 mm.
Dry Adiabatic Lapse Rate (DALR) – The rate at which unsaturated air cools as it rises, approximately 9.8°C per kilometer.
Dry Line – A boundary separating moist air (typically from the Gulf of Mexico) from dry air (from the desert Southwest), a common trigger for severe thunderstorms in the U.S. Plains.
Dust Devil – A small, rotating column of air that lifts dust and debris, forming under clear skies and hot surface conditions.
Dust Storm – A weather event where strong winds lift large amounts of dust into the atmosphere, reducing visibility and causing hazardous conditions.
Dynamic Lifting – The vertical motion of air caused by atmospheric dynamics such as convergence, frontal boundaries, or upper-level divergence.
Dynamics (Atmospheric Dynamics) – The branch of meteorology that deals with the motion of the atmosphere and the forces that cause that motion.
E
Eddy – A circular current of air or water, often small and turbulent, that forms when fluid flow encounters an obstacle or varying pressure.
El Niño – The warm phase of the El Niño–Southern Oscillation (ENSO), characterized by anomalously warm sea surface temperatures in the central and eastern tropical Pacific, affecting global weather patterns.
El Niño–Southern Oscillation (ENSO) – A recurring climate pattern involving changes in sea surface temperatures and atmospheric pressure in the Pacific Ocean. Includes El Niño (warm phase), La Niña (cool phase), and neutral conditions.
Electrical Storm – A thunderstorm characterized by frequent lightning and thunder, often accompanied by rain, hail, or gusty winds.
Electromagnetic Spectrum – The range of all types of electromagnetic radiation, from gamma rays to radio waves. Important in satellite meteorology for remote sensing of Earth’s atmosphere.
Ensemble Forecasting – A method in which multiple model runs (using slightly different initial conditions) are used to estimate forecast uncertainty and probability.
Environment (Meteorological) – The surrounding atmospheric conditions, including temperature, humidity, and wind, in which weather systems develop and evolve.
Equilibrium Level (EL) – The level in the atmosphere where a rising air parcel becomes cooler than its environment and stops rising freely.
Equinox – The time when the sun crosses the celestial equator, resulting in nearly equal day and night lengths. Occurs around March 20 and September 22.
Evaporation – The process by which liquid water becomes vapor. A key part of the water cycle and atmospheric moisture.
Evapotranspiration – The combined process of water loss from soil (evaporation) and plants (transpiration) into the atmosphere.
Extratropical Cyclone – A large-scale low-pressure system that forms outside the tropics, often along fronts, with strong winds and precipitation.
Eye (of a Hurricane) – The calm, clear center of a tropical cyclone, surrounded by the eyewall, where the most intense winds occur.
Eyewall – The ring of intense thunderstorms surrounding the eye of a hurricane. Contains the storm’s strongest winds and heaviest rain.
F
Fallstreak Hole (Hole-Punch Cloud) – A large circular gap that forms in mid- or high-level clouds when supercooled droplets rapidly freeze and fall, often triggered by aircraft.
Fetch – The uninterrupted distance over water that wind blows, influencing wave height and energy.
Flash Flood – A rapid flooding event, typically caused by intense rainfall over a short period, often in mountainous or urban areas.
Flood Warning – Issued when flooding is imminent or already occurring in an area.
Flood Watch – Indicates conditions are favorable for flooding, and residents should be alert.
Fog – A visible suspension of water droplets near the ground, reducing visibility to less than 1 km (0.62 miles).
Foehn Wind – A warm, dry downslope wind on the leeward side of mountains, similar to a Chinook.
Forecast – A prediction of future weather conditions based on observations, models, and meteorological expertise.
Forecast Model – A computer simulation of the atmosphere using mathematical equations and initial data. Examples include the GFS, ECMWF, NAM, and HRRR.
Freezing Drizzle – Supercooled drizzle that freezes upon contact with surfaces, forming a glaze of ice.
Freezing Fog – Fog composed of supercooled droplets that freeze on contact, forming rime ice on surfaces.
Freezing Level – The altitude in the atmosphere where the temperature is 0 °C (32 °F).
Freezing Rain – Rain that freezes upon contact with cold surfaces, forming a layer of ice. Often causes power outages and travel hazards.
Front (Weather Front) – The boundary between two air masses of different temperature and humidity.
Frontal Zone – A broad region that encompasses the temperature gradient and wind shift around a front.
Frost – Ice crystals formed by deposition of water vapor directly onto cold surfaces when air temperature drops below freezing.
Frost Advisory – Issued when frost is expected and may harm crops or plants.
Fujita Scale (F-Scale) – A scale (now largely replaced by the Enhanced Fujita Scale) used to classify tornadoes based on damage.
Funnel Cloud – A rotating, funnel-shaped cloud descending from a thunderstorm, not yet in contact with the ground (unlike a tornado).
G
Gale – A strong wind, typically classified as 34 to 40 knots (39–46 mph), depending on the scale used.
Gamma Radiation – High-energy electromagnetic radiation, used in atmospheric science to detect certain upper-atmosphere processes.
Geopotential Height – The height of a pressure level in the atmosphere relative to sea level, corrected for gravity. Used in upper-air charts.
Glaze – A smooth, transparent layer of ice formed by freezing rain.
Global Climate Model (GCM) – A numerical model that simulates Earth’s climate system over long periods. Used in climate research and IPCC assessments.
Global Forecast System (GFS) – A U.S. weather prediction model run by the National Weather Service that provides global forecasts up to 16 days in advance.
Global Warming – The long-term rise in average global surface temperatures due to increasing greenhouse gases.
Graupel – Soft hail or snow pellets formed when supercooled water droplets freeze onto snowflakes, giving them a lumpy, frosted appearance.
Greenhouse Effect – The natural process by which certain gases (e.g., CO₂, CH₄, H₂O vapor) trap heat in Earth’s atmosphere, keeping the planet habitable.
Greenhouse Gases – Atmospheric gases that absorb and emit infrared radiation, contributing to the greenhouse effect. Includes CO₂, CH₄, N₂O, ozone, and water vapor.
Ground Clutter – Unwanted radar echoes caused by reflections from terrain, buildings, or other non-meteorological sources.
Ground Fog – A shallow fog, usually under 2 meters in depth, forming near the ground, especially in calm, humid conditions.
Gust – A brief, sudden increase in wind speed, usually lasting less than 20 seconds.
Gust Front – A boundary formed by outflowing air from a thunderstorm downdraft, often marked by wind shifts and temperature drops.
Gyre – A large system of rotating ocean currents, influenced by global wind patterns and the Coriolis effect.
H
Hail – Balls or irregular lumps of ice that form in strong thunderstorm updrafts. Hailstones can range in size from peas to grapefruits and cause significant damage to property and crops.
Hailstone – An individual piece of hail, formed by concentric layers of ice deposited around a nucleus during repeated circulation within a storm updraft.
Haines Index – A fire weather index that measures the potential for large wildfire growth based on atmospheric stability and humidity.
Halo – A ring or circle of light that appears around the sun or moon, caused by the refraction of light through ice crystals in cirrostratus clouds.
Hanging Valley – A smaller glacial valley suspended above a main valley, often marked by a waterfall. While a geological term, it sometimes appears in meteorological landscape analysis.
Hard Freeze – A freeze where temperatures drop below 28 °F (−2.2 °C) for at least several hours, likely killing seasonal vegetation.
Hazardous Weather Outlook (HWO) – A National Weather Service product describing potential hazardous weather conditions over the next 7 days.
Heat Advisory – Issued when the heat index is forecast to be dangerously high, usually 100–109 °F (38–43 °C), depending on local criteria.
Heat Burst – A rare, localized downdraft of hot, dry air that descends rapidly, warming adiabatically and causing a sudden spike in temperature.
Heat Dome – A high-pressure system that traps warm air over a region, leading to prolonged heatwaves and stagnant air conditions.
Heat Index – The “feels like” temperature, combining air temperature and relative humidity to reflect how hot conditions feel to humans.
Heat Lightning – Distant lightning flashes that are visible but not accompanied by audible thunder. Usually seen on warm summer nights from distant thunderstorms.
Heat Wave – A prolonged period of abnormally hot weather, often accompanied by high humidity. Definitions vary by region.
Helicity – A measure of the potential for rotating updrafts (mesocyclones) in thunderstorms. High helicity values are associated with increased tornado potential.
High Clouds – Clouds that form above 20,000 feet (6,000 meters), including cirrus, cirrostratus, and cirrocumulus.
High Pressure System – A region of relatively high atmospheric pressure, typically associated with descending air, clear skies, and calm weather.
Humidity – The amount of water vapor in the air. Common measures include relative humidity, specific humidity, and absolute humidity.
Hurricane – A large, organized tropical cyclone with sustained winds of at least 74 mph (119 km/h). Known as a typhoon in the western Pacific and a cyclone in the Indian Ocean.
Hurricane Season – The time of year when tropical cyclones are most likely to form. In the Atlantic, this runs from June 1 to November 30.
Hydrometeor – Any form of water or ice particles suspended in or falling through the atmosphere, including rain, snow, sleet, hail, fog, and cloud droplets.
Hydrology – The study of the movement, distribution, and quality of water, including rainfall, runoff, rivers, and groundwater.
Hydrosphere – All of Earth’s water, including oceans, lakes, rivers, groundwater, glaciers, and water vapor in the atmosphere.
Hydrostatic Equilibrium – A state in which the upward pressure gradient force balances the downward pull of gravity. It keeps the atmosphere from collapsing or flying off into space.
Hypothermia – A medical condition resulting from dangerously low body temperature, often due to prolonged exposure to cold weather or immersion in cold water.
I
Ice Crystals – Small, frozen particles that make up high clouds like cirrus. They can produce optical phenomena like halos and sun dogs.
Ice Fog – A type of fog composed of ice crystals, occurring at very cold temperatures (typically below −30 °C or −22 °F), common in Arctic regions.
Ice Jam – A buildup of ice in rivers or streams that can block water flow and cause flooding.
Ice Pellets (Sleet) – Frozen raindrops that bounce on impact with the ground. Formed when snow melts and refreezes before reaching the surface.
Ice Storm – A storm characterized by freezing rain that accumulates on surfaces, forming a coating of ice that can cause widespread damage.
Indian Summer – A period of warm, dry weather that occurs after the first frost of autumn. The term is dated and considered culturally insensitive in some contexts.
Induced Precipitation – Artificial stimulation of precipitation, typically by cloud seeding with silver iodide or other particles.
Infrared Radiation (IR) – Electromagnetic radiation emitted by Earth and its atmosphere. IR imagery is used in satellite meteorology to estimate temperature and cloud height.
Insolation – Incoming solar radiation received at Earth’s surface. Varies by latitude, season, and cloud cover.
Instability – The tendency of air to rise or sink. Atmospheric instability leads to convection, cloud formation, and often storms.
Intertropical Convergence Zone (ITCZ) – A region near the equator where the trade winds converge, often producing thunderstorms and heavy rainfall.
Inversion (Temperature Inversion) – A layer in the atmosphere where temperature increases with height, suppressing vertical motion and often trapping pollutants.
Ionosphere – A layer of the upper atmosphere ionized by solar radiation, affecting radio communication and satellite transmission.
Irradiance – The amount of solar energy received on a given surface area, usually measured in watts per square meter.
Isallobar – A line on a weather map connecting points of equal pressure change over time.
Isentropic Surface – A surface of constant potential temperature used in dynamic meteorology to analyze atmospheric motion.
Isobar – A line on a weather map connecting points of equal atmospheric pressure. Closer isobars indicate stronger winds.
Isodrosotherm – A line connecting points of equal dew point temperature on a weather map.
Isoheight – A line of constant geopotential height on an upper-air chart.
Isohyet – A line connecting points of equal precipitation on a map.
Isoneph – A line on a weather map connecting areas of equal cloud cover.
Isotherm – A line on a map connecting points of equal temperature.
Isotropic – Having uniform properties in all directions. In meteorology, often used to describe turbulence or radiation fields.
J
Jet Streak – A region within the jet stream where winds are strongest. Jet streaks influence upper-level divergence and vertical motion, aiding storm development.
Jet Stream – A narrow band of strong winds in the upper troposphere, typically flowing from west to east. Jet streams influence weather systems and aircraft routing.
January Thaw – A brief period of unseasonably warm weather during mid to late January, especially in eastern North America.
Joule – A unit of energy used in scientific calculations. In meteorology, it’s commonly used to express CAPE (J/kg).
Juvenile Stage (of a Storm) – The early developmental stage of a storm system, where initial convection or frontal structure begins to organize.
K
Katabatic Wind – A cold, downslope wind that flows from high elevations under the influence of gravity. Examples include the Bora and Mistral.
Kelvin–Helmholtz Instability – A dynamic phenomenon where shear between two layers of fluid creates wave-like cloud patterns.
Kelvin Scale – An absolute temperature scale starting at absolute zero. Common in scientific and thermodynamic equations.
K-H Index (K Index) – A measure of thunderstorm potential based on temperature and moisture in the lower to mid-troposphere. Values over 30 typically indicate storm potential.
Knot (kt) – A unit of speed equal to 1 nautical mile per hour, or approximately 1.15 mph (1.85 km/h). Used for wind speeds and aviation.
L
Lake Breeze – A local wind that blows from a lake toward land during the day due to temperature differences between land and water.
Lake-Effect Snow – Snowfall produced when cold air passes over a warmer lake, picking up moisture and heat, then depositing snow downwind.
Land Breeze – A nighttime wind that blows from the land toward the water as land cools more quickly than water.
Lapse Rate – The rate of temperature decrease with altitude. Key lapse rates include:
- Dry Adiabatic Lapse Rate (DALR): ~9.8 °C/km
- Moist Adiabatic Lapse Rate (MALR): ~5–7 °C/km
- Environmental Lapse Rate (ELR): The observed lapse rate at a specific location/time
Latent Heat – Heat energy released or absorbed during phase changes of water (e.g., condensation, evaporation). Drives many atmospheric processes, including storm development.
Latitude – The geographic coordinate that specifies the north–south position on Earth. Latitude influences climate and insolation.
La Niña – The cool phase of the ENSO cycle, characterized by colder-than-normal sea surface temperatures in the central and eastern Pacific, affecting global weather.
Landfall – The moment when the center of a tropical cyclone crosses a coastline.
Layered Clouds – Clouds that form in sheets or layers, typically associated with stable air and widespread precipitation (e.g., stratus, altostratus).
Leeward – The downwind side of a mountain or object. Often drier and warmer due to adiabatic warming of descending air.
Level of Free Convection (LFC) – The altitude at which a rising air parcel becomes warmer than its environment and accelerates upward without external forcing.
Lidar – Light Detection and Ranging. A remote sensing technology that uses lasers to measure particles, aerosols, or cloud height in the atmosphere.
Lifted Condensation Level (LCL) – The height at which rising air becomes saturated and condensation begins, forming cloud base.
Lifted Index (LI) – A stability index calculated by comparing the temperature of a lifted air parcel to its environment at 500 mb. Negative values indicate instability.
Lightning – A sudden electrostatic discharge between regions of opposite charge in a cloud, between clouds, or between a cloud and the ground.
Lightning Strike – The actual path or discharge channel of a lightning bolt. Can heat the air to over 30,000 °C (54,000 °F).
Longwave Radiation – Infrared radiation emitted by Earth’s surface and atmosphere. Plays a key role in Earth’s energy balance.
Low Clouds – Clouds that form below 6,500 feet (2,000 meters), such as stratus and stratocumulus.
Low-Level Jet (LLJ) – A region of strong winds in the lower atmosphere (typically 850–700 mb), often transporting moisture and energy into storm systems.
Low Pressure System – A region of lower atmospheric pressure relative to its surroundings, associated with rising air, cloud formation, and precipitation.
Lull – A temporary decrease in wind speed or weather activity.
Lysimeter – A scientific instrument used to measure evapotranspiration and water balance in soil–plant systems. Occasionally referenced in hydrometeorology studies.
M
Macroscale – The largest scale of atmospheric motion, covering thousands of kilometers. Includes global wind patterns and large extratropical cyclones.
Marine Layer – A shallow layer of cool, moist air trapped under a temperature inversion near large bodies of water, often bringing coastal fog or low clouds.
Maximum Temperature – The highest air temperature recorded during a specified time period, typically 24 hours.
Mean Sea Level Pressure (MSLP) – Atmospheric pressure reduced to sea level, used as a baseline for comparing surface pressures at different elevations.
Measured Ceiling – The lowest cloud layer (reported in feet above ground level) that covers more than half the sky, measured by automated or human observation.
Medium Range Forecast – A weather forecast typically spanning 3 to 10 days in the future.
Mesocyclone – A rotating updraft within a supercell thunderstorm, typically 2–10 km in diameter. Often a precursor to tornado formation.
Mesonet – A dense network of automated weather stations that measure surface meteorological variables at high temporal resolution.
Mesoscale – The middle scale of meteorological phenomena, ranging from a few kilometers to several hundred. Includes thunderstorms, squall lines, sea breezes, and mountain-valley circulations.
Mesoscale Convective Complex (MCC) – A large, organized cluster of thunderstorms that can persist for several hours, often overnight. Defined by size, symmetry, and duration in satellite imagery.
Mesoscale Convective System (MCS) – A general term for organized groups of thunderstorms acting as a single system, such as squall lines, MCCs, or bow echoes.
Meteorologist – A scientist who studies the atmosphere and weather processes, often specializing in forecasting, research, or broadcasting.
Meteorology – The scientific study of the atmosphere and its phenomena, including weather forecasting, climate studies, and atmospheric dynamics.
Microbarograph – An instrument that records small, rapid changes in atmospheric pressure, used for storm and wave studies.
Microburst – A small, intense downdraft from a thunderstorm that spreads out horizontally upon hitting the ground. Can be wet (with rain) or dry, and cause aircraft hazards.
Microscale – The smallest atmospheric scale, typically under 2 km. Includes turbulence, wind gusts, and small eddies.
Millibar (mb) – A unit of atmospheric pressure. 1 mb = 100 pascals. Standard sea-level pressure is 1013.25 mb.
Minimum Temperature – The lowest air temperature recorded during a given time period, typically overnight or within 24 hours.
Mist – Tiny water droplets suspended in the air, reducing visibility less than fog but more than haze. Often occurs with light winds and high humidity.
Mixing Ratio – The mass of water vapor in a given mass of dry air, usually expressed in grams per kilogram (g/kg).
Moderate Risk – A categorical risk level issued by the Storm Prediction Center (SPC), indicating a significant potential for severe weather including tornadoes or widespread damaging wind or hail.
Moisture Convergence – The accumulation of water vapor in a region due to the convergence of moist air, often leading to cloud formation and precipitation.
Monsoon – A seasonal reversal of wind accompanied by a dramatic shift in precipitation patterns. Most notably occurs in South and Southeast Asia.
Mountain Breeze – A downslope wind that occurs at night when mountain slopes cool more rapidly than valleys, causing air to flow downhill.
Mountain Wave – A wave pattern formed when stable air flows over a mountain barrier, often resulting in turbulent eddies and lenticular clouds.
Multicell Thunderstorm – A storm consisting of multiple updraft/downdraft cells in different stages of development. Can produce hail, strong winds, and isolated tornadoes.
N
National Centers for Environmental Prediction (NCEP) – A division of NOAA responsible for producing and distributing national weather forecasts and guidance.
National Hurricane Center (NHC) – A branch of the National Weather Service that monitors and forecasts tropical cyclones in the Atlantic and eastern Pacific Oceans.
National Oceanic and Atmospheric Administration (NOAA) – A U.S. federal agency responsible for weather, ocean, and atmospheric science, including the National Weather Service and NHC.
National Weather Service (NWS) – A division of NOAA that provides weather, water, and climate forecasts and warnings for the United States.
Negative Tilt Trough – A trough axis that tilts from the northwest to southeast. Often associated with enhanced storm development due to strong divergence aloft.
Net Radiation – The balance between incoming and outgoing radiation at Earth’s surface. Affects surface heating, evaporation, and climate.
Neutral Stability – A state in which an air parcel remains at its displaced altitude because it has the same temperature as its surroundings.
Nimbostratus – Thick, dark gray clouds that produce continuous precipitation and cover large areas of the sky. Typically associated with warm fronts.
Nocturnal Inversion – A temperature inversion that forms near the ground at night as the surface cools through radiation.
Nor’easter – A powerful extratropical cyclone affecting the U.S. East Coast, typically bringing heavy precipitation and strong northeast winds.
Normalized CAPE (NCAPE) – A modified form of Convective Available Potential Energy that accounts for the depth of the buoyant layer. Useful for comparing instability across different environments.
Numerical Weather Prediction (NWP) – The use of mathematical models and computer simulations to forecast the weather based on current observations.
Nowcasting – Very short-range weather forecasting (0–2 hours ahead) using real-time data such as radar, satellite, and surface observations.
Nucleation – The initial formation of cloud droplets or ice crystals around a particle (condensation nuclei or ice nuclei).
NWP Model Bias – Systematic error inherent in a forecast model due to assumptions or limitations in its physics or resolution.
O
Occluded Front – A boundary that forms when a cold front overtakes a warm front, lifting the warm air aloft. Often associated with mature extratropical cyclones and widespread precipitation.
Occlusion (Cyclone) – The process during which a developing cyclone reaches maturity, and the warm sector is completely lifted off the surface.
Offshore Flow – Winds that blow from land to water, often associated with dry conditions and sometimes leading to elevated fire danger.
Omega Block – A persistent upper-level high-pressure pattern resembling the Greek letter Ω, flanked by low-pressure systems. Known for producing stagnant weather conditions.
Open Wave – A stage in cyclone development where a low-pressure system has not yet occluded. Features well-defined warm and cold fronts.
Optical Phenomena – Atmospheric visual effects such as halos, sundogs, coronas, and rainbows, caused by interaction of light with ice crystals or water droplets.
Orographic Clouds – Clouds formed when air is forced to rise over mountains or elevated terrain, cooling and condensing in the process.
Orographic Lift – Upward motion of air caused by topography (e.g., mountains), often resulting in cloud formation and precipitation on the windward side.
Outflow – Air that flows outward from a storm system or thunderstorm, typically at or near the surface. Can reinforce new storm development.
Outflow Boundary – The leading edge of cooler air from a storm downdraft that acts like a mini cold front. Can trigger new thunderstorms.
Overcast – A cloud cover condition in which more than 90% of the sky is covered by clouds.
Overrunning – A meteorological process where warm, moist air slides up and over a cooler air mass, often producing steady precipitation.
Overshooting Top – A dome-like protrusion above the anvil of a thunderstorm, caused by a strong updraft that penetrates the tropopause. Indicates severe storm potential.
Ozone (O₃) – A triatomic molecule of oxygen that exists in the stratosphere (where it absorbs UV radiation) and near the surface (where it acts as a pollutant).
Ozone Hole – A seasonal depletion of stratospheric ozone over Antarctica, primarily due to chlorofluorocarbons (CFCs).
P
Parcel (Air Parcel) – A hypothetical volume of air used in thermodynamic analysis, assumed to be uniform in properties and isolated from its surroundings except for pressure.
Partial Pressure – The pressure exerted by a single gas in a mixture of gases. For example, water vapor exerts its own partial pressure within air.
Peak Wind – The highest instantaneous wind speed recorded during a specific observation period.
Permafrost – Permanently frozen ground found in Arctic and sub-Arctic regions. Thawing can influence local weather and release greenhouse gases.
Photochemical Smog – A type of air pollution formed by sunlight-driven chemical reactions involving nitrogen oxides and volatile organic compounds.
Planetary Boundary Layer (PBL) – The lowest part of the atmosphere directly influenced by the Earth’s surface. Turbulent and responsive to diurnal heating and friction.
Polar Front – The boundary between cold polar air and warmer mid-latitude air. Plays a major role in mid-latitude cyclone development.
Polar Jet Stream – A fast-moving ribbon of air found near the tropopause in mid- to high latitudes. Separates cold polar air from warmer air to the south.
Polar Vortex – A large-scale cyclonic circulation around the poles, strongest in winter. When disrupted, it can allow frigid Arctic air to spill southward.
Potential Energy – Stored energy due to position or configuration. In meteorology, relates to buoyancy and lifting of air parcels.
Potential Temperature – The temperature an air parcel would have if brought adiabatically to a standard pressure level (typically 1000 mb).
Precipitable Water (PWAT) – The total amount of water vapor in a vertical column of air. High PWAT values suggest potential for heavy rainfall.
Precipitation – Any form of water—liquid or solid—that falls from the atmosphere to the ground, including rain, snow, sleet, hail, drizzle, and freezing rain.
Pressure – The force exerted by the weight of the atmosphere above a point. Measured in millibars (mb) or hectopascals (hPa).
Pressure Gradient – The rate of pressure change over a given distance. Drives wind; stronger gradients produce higher winds.
Pressure Tendency – The change in atmospheric pressure over time at a location. Rising pressure usually signals improving weather; falling pressure indicates stormy conditions.
Prevailing Winds – The most common wind direction in a region. For example, westerlies prevail in the mid-latitudes.
Probability of Precipitation (PoP) – The likelihood, expressed as a percentage, that measurable precipitation will occur at a given location during a specific time window.
Psychrometer – A device with two thermometers (wet-bulb and dry-bulb) used to measure humidity.
Pulse Storm – A single-cell thunderstorm that intensifies rapidly due to high instability but has little wind shear, leading to short-lived but intense weather (e.g., hail, downbursts).
PVA (Positive Vorticity Advection) – A dynamic forcing mechanism where vorticity is transported into a region, leading to rising air and enhanced storm development.
Q
Q-G Theory (Quasigeostrophic Theory) – A simplified mathematical framework used in meteorology to describe large-scale atmospheric flow and vertical motion, assuming small deviations from geostrophic balance.
QPF (Quantitative Precipitation Forecast) – A forecast indicating the expected amount of liquid-equivalent precipitation over a specific period and area.
QPF Grid – A digital grid of QPF values used in model guidance and official forecasts.
Quasi-Stationary Front – A frontal boundary that exhibits little or no movement, often leading to prolonged periods of rain or storms on one or both sides.
Quasi-Zonal Flow – An upper-level wind pattern where the flow is mostly west-to-east with minimal north–south amplitude, leading to less dramatic weather shifts.
Quenching (Lightning) – The process by which a lightning discharge is terminated by the exhaustion of electrical potential or collision with an oppositely charged region.
Quiescent Weather – Calm and uneventful weather conditions, often under high pressure and associated with clear skies and light winds.
R
Radar – Radio Detection and Ranging. A system that uses reflected radio waves to detect precipitation, storm intensity, and motion.
Radar Echo – The return signal from radar indicating the presence of precipitation or objects. Stronger echoes often correlate with heavier precipitation.
Radiation – The transfer of energy in the form of electromagnetic waves. Includes shortwave solar radiation and longwave terrestrial radiation.
Radiation Fog – A fog that forms when the Earth’s surface cools rapidly by radiation, causing the air near the ground to reach its dew point. Common on clear, calm nights.
Radiational Cooling – The process by which the Earth’s surface loses heat via longwave radiation, often leading to nighttime temperature drops.
Radiosonde – An instrument package carried by a weather balloon that measures temperature, humidity, and pressure through the atmosphere.
Rain – Liquid precipitation that falls when atmospheric temperatures are above freezing throughout the column of air.
Rain Gauge – A device used to collect and measure the amount of rainfall over a specified period.
Rain Shadow – A dry region on the leeward side of a mountain range, created when moist air rises and condenses on the windward side, leaving dry air to descend on the other.
Rapid Intensification – A sharp increase in the strength of a tropical cyclone, defined as a ≥35 mph (30 kt) increase in maximum sustained winds over 24 hours.
Rawinsonde – A radiosonde equipped with a radio tracking system to measure wind speed and direction in addition to other atmospheric variables.
Rayleigh Scattering – The preferential scattering of short-wavelength light (blue) by small particles in the atmosphere, explaining why the sky appears blue.
Real Feel – A proprietary index combining multiple factors such as temperature, humidity, wind, and solar radiation to estimate how the weather “feels” to the human body.
Relative Humidity (RH) – The percentage of water vapor present in the air relative to the maximum amount the air can hold at that temperature.
Relative Vorticity – A measure of the local spin of air in the atmosphere due to both curvature and shear of the flow.
Residual Layer – A remnant atmospheric layer left behind after the dissipation of the daytime boundary layer. Can affect air quality and stability overnight.
Ridge – An elongated region of relatively high atmospheric pressure, usually associated with warm and dry weather.
Rime – A white, opaque deposit of ice formed when supercooled water droplets freeze on contact with surfaces. Common in freezing fog or wind-driven icing events.
Rip Current – A narrow, fast-moving channel of water flowing from the shore out to sea. Often mistaken for undertow and hazardous to swimmers.
Rossby Waves – Large-scale meanders in high-altitude winds, such as the jet stream, driven by Earth’s rotation. Influence weather patterns and the movement of storm systems.
Runoff – Water from precipitation that flows over land into rivers, lakes, or oceans rather than being absorbed into the ground.
RVR (Runway Visual Range) – The horizontal visibility distance a pilot can expect to see down a runway. Critical for aviation safety, especially in fog or low visibility.
S
Saturation – The point at which air holds the maximum amount of water vapor possible at a given temperature. Any additional moisture results in condensation.
Saturation Mixing Ratio – The maximum possible amount of water vapor (by mass) that air can contain at a specific temperature and pressure.
Scattered Clouds – A sky condition in which 25% to 50% of the sky is covered by clouds. Used in aviation and weather reports.
Sea Breeze – A local wind that blows from the sea toward land, caused by temperature differences between land and water during the daytime.
Sea-Level Pressure – Atmospheric pressure corrected to mean sea level. Used to compare surface pressures regardless of elevation.
Seiche – A standing wave in an enclosed or partially enclosed body of water, often caused by atmospheric pressure changes or strong winds.
Sensitivity (Radar) – The ability of a radar system to detect weak echoes, such as light rain or small particles.
Severe Thunderstorm – A thunderstorm that produces one or more of the following: hail ≥1 inch (2.5 cm), winds ≥58 mph (93 km/h), or a tornado.
Severe Thunderstorm Watch – Issued by the SPC when conditions are favorable for the development of severe thunderstorms over a large area.
Severe Thunderstorm Warning – Issued when a severe thunderstorm has been detected or observed and poses a threat to life or property.
Shear (Wind Shear) – A change in wind speed and/or direction over a short distance in the atmosphere. Critical in storm development and aviation safety.
Shortwave – A small-scale trough in the upper atmosphere that enhances lift and can trigger or strengthen storms.
Shower – Precipitation that is intermittent, often brief, and falls from cumuliform clouds. Can be rain, snow, or ice pellets.
Sleet – Frozen raindrops that form when snow melts in a warm layer aloft and refreezes before reaching the ground.
Sling Psychrometer – A hand-held device with two thermometers (wet and dry bulb) used to measure relative humidity by swinging it in the air.
Snow – Precipitation consisting of ice crystals that form and aggregate in the atmosphere, falling to the ground when temperatures are below freezing.
Snow Flurries – Brief and light snowfall with little or no accumulation.
Snow Squall – An intense but short-lived burst of heavy snowfall, often accompanied by strong winds and rapid visibility reduction.
Sounding – A vertical profile of temperature, humidity, and wind in the atmosphere, typically obtained from radiosonde data.
Specific Humidity – The ratio of water vapor mass to the total mass of air in a parcel. Unlike relative humidity, it does not change with temperature.
SPC (Storm Prediction Center) – A division of the National Weather Service responsible for issuing severe weather watches and forecasts in the United States.
Squall – A sudden, sharp increase in wind speed lasting minutes, often associated with a line of thunderstorms.
Squall Line – A line of thunderstorms that can stretch for hundreds of miles, producing severe winds, hail, and sometimes tornadoes.
Stability – The tendency of the atmosphere to resist or promote vertical motion. Stable air suppresses convection; unstable air enhances it.
Stable Layer – A layer in the atmosphere where vertical motion is inhibited, often due to a temperature inversion.
Stationary Front – A boundary between air masses that is not moving appreciably, often producing prolonged cloudiness and precipitation.
Steering Flow – The large-scale wind patterns in the mid- and upper-levels of the atmosphere that influence the movement of storms and tropical cyclones.
Storm – A disturbed state of the atmosphere involving precipitation, wind, thunder, lightning, or other severe conditions.
Storm Surge – A rise in sea level caused by strong winds and low pressure from a tropical cyclone. The most dangerous hazard of hurricanes.
Storm Track – The projected or historical path of a storm system.
Stratiform Clouds – Cloud formations that are generally layered and cover large areas, as opposed to cumuliform (heaped) clouds.
Stratocumulus – Low, lumpy clouds that often cover the sky in patches or layers. May produce light precipitation.
Stratosphere – The layer of the atmosphere above the troposphere, extending from about 10 km to 50 km altitude. Contains the ozone layer.
Stratus – Low, gray, and uniform clouds that often cover the sky and may produce drizzle or light snow.
Subfreezing – Air or surface temperatures below 32 °F (0 °C).
Subsidence – The downward movement of air in the atmosphere. Often associated with high pressure, warming, and cloud dissipation.
Sublimation – The direct transition of a substance from solid to gas phase without passing through the liquid phase. For example, ice turning into vapor.
Sundog – A bright spot in the sky caused by the refraction of sunlight through ice crystals, appearing as a mock sun to the left or right of the real sun.
Supercell – A highly organized, long-lived thunderstorm with a rotating updraft (mesocyclone). Capable of producing severe weather including strong tornadoes.
Surface Map – A weather map that displays observations of temperature, pressure, dew point, wind, and cloud cover at ground level.
SWA (Southwest Flow Aloft) – A synoptic setup where mid- to upper-level winds come from the southwest. Associated with moisture transport and storm development.
Synoptic Scale – The large-scale features of the atmosphere, such as fronts, troughs, and high/low pressure systems, typically hundreds to thousands of kilometers in size.
T
Temperature – A measure of the average kinetic energy of molecules in a substance. Reported in degrees Fahrenheit (°F), Celsius (°C), or Kelvin (K).
Thermal – A column of rising air created by surface heating. Often a source of lift for gliders and birds.
Thermocline – A layer in a body of water where temperature changes rapidly with depth. Important in ocean-atmosphere interactions.
Thermodynamics (Atmospheric) – The study of heat, energy, and phase changes in atmospheric processes.
Thermograph – An instrument that records temperature continuously over time.
Thermometer – A device used to measure air temperature.
Thunder – The sound caused by the rapid expansion of air heated by a lightning bolt.
Thundersnow – A rare event where snow falls during a thunderstorm. Accompanied by lightning and thunder.
Thunderstorm – A convective storm containing lightning and thunder, often with heavy rain, hail, wind, and sometimes tornadoes.
Tilted Updraft – An updraft that is slanted rather than vertical due to wind shear. Important for maintaining storm structure and preventing precipitation fallout into the inflow.
Tornado – A violently rotating column of air extending from the base of a thunderstorm to the ground. Rated on the EF-Scale.
Tornado Alley – A colloquial term for the region of the central U.S. where tornadoes are most frequent and intense, especially during spring.
Tornado Warning – Issued when a tornado has been sighted or detected by radar. Action should be taken immediately.
Tornado Watch – Issued when conditions are favorable for tornado development within the watch area.
Towering Cumulus – A large cumulus cloud with significant vertical growth, often a precursor to a thunderstorm.
Trade Winds – Steady easterly winds found in the tropics, caused by the Coriolis effect and Hadley circulation.
Transpiration – The release of water vapor from plant leaves into the atmosphere.
Tropical Cyclone – A warm-core low-pressure system that forms over tropical waters, ranging from tropical depressions to hurricanes and typhoons.
Tropical Depression – A tropical cyclone with maximum sustained winds of 38 mph (33 knots) or less.
Tropical Disturbance – A cluster of showers and thunderstorms over tropical waters with minimal organization and no closed circulation.
Tropical Storm – A tropical cyclone with maximum sustained winds of 39 to 73 mph (34–63 knots).
Tropics – The region of Earth between the Tropic of Cancer and Tropic of Capricorn, characterized by year-round warmth.
Tropopause – The boundary between the troposphere and stratosphere. Marks the top of most weather systems.
Troposphere – The lowest layer of Earth’s atmosphere, extending from the surface to the tropopause. Weather occurs here.
Trough – An elongated area of low pressure, often associated with cloudiness and precipitation. Troughs can trigger rising air and storms.
Tsunami – A series of ocean waves caused by underwater earthquakes, volcanic eruptions, or landslides. Not a meteorological phenomenon, but sometimes confused with storm surge.
Turbulence – Irregular motion of air resulting in eddies and up/down drafts. Common near mountains, jet streams, and thunderstorms.
Twister – A colloquial term for a tornado.
Typhoon – The term for a hurricane in the western Pacific Ocean. Structurally identical to a tropical cyclone or hurricane.
U
Ultraviolet (UV) Radiation – Invisible solar radiation with wavelengths shorter than visible light. Overexposure causes sunburn and skin damage.
Ultraviolet Index (UV Index) – A forecast of expected risk from UV exposure on a scale from 0 (low) to 11+ (extreme). Influenced by cloud cover, time of year, and ozone concentration.
Unstable Air – Air that is warmer and/or more humid than its surroundings, making it buoyant and prone to rising, which can lead to cloud development and storms.
Updraft – An upward current of air within a storm or cumulus cloud. Strong updrafts support hail formation and thunderstorm longevity.
Upper-Level Low – A closed low-pressure system located aloft (usually 500 mb level or above) that may not be reflected at the surface.
Upper-Air Sounding – A vertical profile of temperature, humidity, and wind, typically collected by a radiosonde balloon and used to assess atmospheric stability.
Upslope Flow – Air that moves up an incline such as a mountain slope, cooling adiabatically and often causing clouds and precipitation.
Urban Heat Island (UHI) – A localized area of higher temperature in a city due to human activity, asphalt, and reduced vegetation.
UV Radiation – See Ultraviolet Radiation.
V
Valley Breeze – A local upslope wind that develops during the daytime in mountainous areas as valley air heats and rises.
Vapor Pressure – The pressure exerted by water vapor in the air. Related to humidity and evaporation potential.
Veering Winds – Winds that change direction clockwise with height or time (in the Northern Hemisphere), often indicating warm air advection.
Vertical Wind Shear – A change in wind speed and/or direction with height. Crucial in storm organization and tornado potential.
Virga – Precipitation that falls from a cloud but evaporates before reaching the ground, often visible as streaks beneath clouds.
Visibility – The maximum distance at which an object can be clearly seen. Affected by fog, precipitation, smoke, or haze.
Vorticity – A measure of rotation in the atmosphere. Positive vorticity is associated with cyclonic (counterclockwise in the Northern Hemisphere) motion.
Vortex – A spinning, turbulent flow of air, such as in tornadoes, waterspouts, or mesocyclones.
Vorticity Advection – The transport of vorticity (spin) by the wind. Positive vorticity advection often promotes upward motion and storm development.
W
Wall Cloud – A lowered, rotating cloud base beneath the updraft of a thunderstorm. Often the location where tornadoes form.
Warm Front – The boundary where a warm air mass overtakes a retreating cooler air mass. Associated with steady, widespread precipitation.
Warm Sector – The region between the warm and cold fronts of a mid-latitude cyclone. Often unstable and favorable for severe weather.
Warning (Weather Warning) – Issued when hazardous weather is imminent or occurring. Indicates that immediate action is necessary to protect life and property.
Watch (Weather Watch) – Issued when conditions are favorable for hazardous weather to develop. Signals the need for preparedness and monitoring.
Water Vapor – The gaseous form of water in the atmosphere. A major greenhouse gas and critical to cloud and storm formation.
Waterspout – A tornado-like vortex over a body of water. Can be fair-weather or associated with strong thunderstorms.
Wave Cloud – A cloud that forms in response to atmospheric waves, often downwind of mountain ranges. Lenticular clouds are an example.
Weather – The current state of the atmosphere at a specific time and place, including temperature, humidity, precipitation, wind, and visibility. In contrast, climate is a long-term situation.
Weather Balloon – A balloon filled with hydrogen or helium that carries instruments aloft to collect upper-air observations.
Weather Front – A boundary separating two different air masses. Includes cold fronts, warm fronts, occluded fronts, and stationary fronts.
Weathering – While primarily a geological term, weathering refers to the breakdown of rocks by atmospheric processes including rain and temperature change.
Whiteout – A condition of severely reduced visibility due to snow-covered surfaces and blowing snow. Common in blizzards and polar regions.
Wind – The movement of air caused by differences in pressure, affected by Earth’s rotation and friction.
Wind Advisory – Issued when sustained winds or gusts reach levels that may be hazardous but do not meet warning criteria.
Wind Chill – The perceived decrease in air temperature due to wind, which increases heat loss from exposed skin.
Wind Gust – A brief increase in wind speed, typically lasting less than 20 seconds and exceeding the average wind speed.
Wind Shear – See Vertical Wind Shear.
Windward – The side of a mountain or object facing the wind. Receives more precipitation due to orographic lift.
Winter Storm Warning – Issued for severe winter weather including heavy snow, ice, or a combination thereof.
WMO (World Meteorological Organization) – A specialized agency of the United Nations that coordinates global meteorological observations and practices.
X
X-Band Radar – A weather radar operating at wavelengths of 2.5–4 cm. Useful for detecting small-scale precipitation but more susceptible to attenuation.
X-Ray Solar Flare – A sudden burst of high-energy radiation from the sun, which can disrupt satellite communications and GPS. Tracked by space weather agencies, not typical weather services.
Y
Yellow Snow Warning – Not an official meteorological term. Sometimes used humorously or metaphorically. “Yellow” in official warnings usually refers to moderate-level alerts in some international systems.
Y-Intercept (in Trendlines) – While not a weather term per se, it may appear in regression analysis of climate data or atmospheric trends.
Z
Zonal Flow – Atmospheric circulation where winds flow parallel to latitude lines. Leads to milder and more stable weather.
Z-R Relationship – A mathematical relationship between radar reflectivity (Z) and rainfall rate (R), used to estimate precipitation amounts from radar data.
References
- Geer, Ira W., ed. (1996). Glossary of Weather and Climate, with Related Oceanic and Hydrologic Terms. Boston, Mass.: American Meteorological Society. ISBN 1878220195.
- Smith, Jacqueline, ed. (2001). The Facts on File Dictionary of Weather and Climate. New York: Facts on File. ISBN 9780816045327.