| Ablation | Depletion of snow and ice by melting and evaporation. … | |
| Absorption | The process in which incident radiant energy is retained by a substance by conversion to … | |
| Accretion | The growth of a precipitation particle by the collision of a frozen particle with a … | |
| Adiabat | A line on a thermodynamic chart relating the pressure and temperature of a substance (such … | |
| Adiabatic | Changes in temperature caused by the expansion (cooling) or compression (warming) of a body of … | |
| Adiabatic Lapse Rate | The rate of decrease of temperature experienced by a parcel of air when it is … | |
| Advection | Transport of an atmospheric property by the wind. … | |
| Air Mass | A body of air covering a relatively wide area and exhibiting horizontally uniform properties. … | |
| Air Mass Thunderstorm | Generally, a thunderstorm not associated with a front or other type of synoptic-scale forcing mechanism. … | |
| Albedo | Reflectivity; the fraction of radiation striking a surface that is reflected by that surface. … | |
| Alberta Clipper | A fast moving low pressure system that moves southeast out of Canadian Province of Alberta … | |
| Aleutian Low | A semi-permanent, subpolar area of low pressure located in the Gulf of Alaska near the … | |
| Altostratus | A cloud of a class characterized by a generally uniform gray sheet or layer, lighter … | |
| Anemometer | An instrument used for measuring the speed of the wind. … | |
| ANOMALOUS PROPAGATION | Non-standard atmospheric temperature or moisture gradients will cause all or part of the radar beam … | |
| Anticyclone | A large-scale circulation of winds around a central region of high atmospheric pressure, clockwise in … | |
| Anvil | The flat, spreading top of a cumulonimbus cloud, often shaped like an anvil. Thunderstorm anvils … | |
| Arctic Oscillation | The Arctic Oscillation is a pattern in which atmospheric pressure at polar and middle latitudes … | |
| Arcus | A low, horizontal cloud formation associated with the leading edge of thunderstorm outflow (i.e., the … | |
| Azores High | Alternate term for Bermuda High – a semi-permanent, subtropical area of high pressure in the … | |