NAV Brasil Aeronautical Meteorologist key terms

The rate at which air temperature decreases with increasing height in the atmosphere, usually expressed in degrees Celsius per thousand feet or per kilometer, and compared against the dry and saturated adiabatic rates.

The fixed rate of about 9.8 degrees Celsius per kilometer at which an unsaturated parcel cools when lifted, because no latent heat is released during expansion.

The actual measured rate of temperature decrease with height in the surrounding atmosphere at a given place and time, determined from soundings rather than from parcel theory.

The temperature an air parcel would have if brought adiabatically to a standard reference pressure, usually 1000 hPa; it is conserved during dry adiabatic processes and labels air masses.

The potential temperature an air parcel would reach after all its water vapor condensed and latent heat was released; it is conserved in moist adiabatic processes and helps identify air masses and instability.

A layer in which temperature increases with height instead of decreasing, suppressing vertical mixing and often trapping moisture, haze, or pollutants beneath it.

The amount of buoyant energy, measured in joules per kilogram, that a rising air parcel can gain between its level of free convection and its equilibrium level; larger values favor stronger thunderstorms.

The height at which a lifted parcel becomes warmer than its surroundings and therefore rises spontaneously without further forcing.

The height at which a parcel lifted from the surface first becomes saturated when cooled at the dry adiabatic rate, marking the base of convective cloud.

The height at which air cooled by forced ascent reaches saturation, commonly taken as the base of stratiform or cumuliform cloud layers.

The ratio, expressed as a percentage, of the actual water vapor content of air to the maximum amount it could hold at the same temperature and pressure.

The temperature to which air must be cooled at constant pressure and moisture content for saturation to occur; a small spread between dew point and temperature indicates high humidity and possible fog or low cloud.

A suspension of water droplets near the surface that reduces horizontal visibility below 1000 meters; aviation operations require specific minima and reporting when it occurs.

The theoretical horizontal wind that results from exact balance between the horizontal pressure gradient force and the Coriolis force, blowing parallel to straight isobars above the friction layer.

An apparent force caused by the Earth's rotation that deflects moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, proportional to wind speed and latitude.

The force per unit mass that accelerates air from higher toward lower pressure; its strength depends on how closely isobars are spaced on a constant-height chart.

A line on a weather chart joining places of equal mean sea level pressure; spacing between isobars indicates the strength of the pressure gradient and hence surface wind speed.

A narrow, strong band of upper-tropospheric wind, often exceeding 60 knots, associated with sharp temperature contrasts and important for flight planning and clear air turbulence.

A large-scale meander of the upper-level westerly flow generated by variations of the Coriolis parameter with latitude, controlling trough and ridge placement and mid-latitude weather systems.

An elongated region of relatively low pressure or low height on a weather chart, typically associated with ascending motion, cloudiness, and precipitation ahead of it.

An elongated region of relatively high pressure or high height on a weather chart, usually linked to subsidence, clear skies, and generally favorable flying conditions.

The transition zone between two air masses of different temperature and humidity, classified as cold, warm, stationary, or occluded according to how it moves and evolves.

The front formed when a faster-moving cold front overtakes a warm front and lifts the warm sector air off the surface, often producing extensive cloud and precipitation.

The mechanism by which temperature contrasts between air masses generate and intensify mid-latitude cyclones and their associated frontal systems.

A change of wind speed or direction over a short vertical or horizontal distance near the surface, hazardous during takeoff and landing and reportable in specific formats.

A localized, intense downdraft from a convective cloud that spreads out at the surface, producing strong divergent winds and severe danger to aircraft on approach or departure.

Turbulence occurring in cloud-free air, most often near jet streams and upper-level frontal boundaries, invisible to the eye and to conventional weather radar.

A change in wind vector between two points in space, which can produce turbulence and abrupt changes in airspeed and lift, especially during climb and descent.

The length of path in the atmosphere over which light transmission is reduced to about five percent, used as the physical basis for measuring and reporting runway visual range.

The distance over which a pilot on the runway centerline can see markings or lights, reported in meters and used to determine takeoff and landing minima.

An instrument that measures the fraction of light transmitted across a known baseline to estimate visibility and runway visual range.

An instrument package carried aloft by a balloon that measures pressure, temperature, humidity, and wind with height, producing a sounding used in analysis and model assimilation.

A remote sensing system that detects precipitation and measures the radial velocity of hydrometeors, revealing wind structure, gust fronts, and rotation within storms.

An Earth-orbiting platform positioned over the equator at about 36,000 kilometers altitude, providing continuous imagery of the same hemisphere at intervals of minutes.

A low-altitude platform that circles the Earth in a near-polar orbit, offering higher spatial resolution imagery at fixed local times but less frequent coverage of a given area.

The technique of combining observations with a short-range model forecast to produce the best possible initial state for a numerical weather prediction run.

The use of mathematical models of the atmosphere, solved on a grid, to forecast future weather from an analyzed initial state.

Aerodrome forecast issued under ICAO provisions, giving expected conditions at an aerodrome over a stated period, including wind, visibility, weather, cloud, and significant changes.

A routine aerodrome weather report issued at half-hourly or hourly intervals, describing observed surface wind, visibility, weather, cloud, temperature, dew point, and pressure.

A special aerodrome weather report issued when significant changes in wind, visibility, weather, or cloud occur between routine reports, affecting aircraft operations.

A short statement appended to a local routine report indicating expected significant changes at the aerodrome within the following two hours.

A meteorological information message issued to warn of specified en-route weather phenomena such as severe turbulence, severe icing, volcanic ash, or tropical cyclones that may affect flight safety.

Information issued to warn of en-route weather phenomena that may affect low-level flights but fall below SIGMET severity, such as moderate turbulence or mountain obscuration.

A message, coordinated internationally, providing information on the location and movement of volcanic ash clouds that pose a hazard to aviation.

Predefined aerodrome procedures activated when visibility or cloud base falls below specified values, involving additional observations, reports, and coordination with air traffic services.

An aerodrome to which a flight may proceed if landing at the intended destination becomes impossible or inadvisable, requiring appropriate weather minima in the flight plan.