Weather Glossary – A


ACID RAIN – Cloud or rain droplets containing pollutants, such as oxides of sulfur and nitrogen, to make them acidic.

ADIABATIC – changes in temperature caused by the expansion (cooling) or compression (warming) of a body of air as it rises or descends in the atmosphere.

ADNLY– Additionally

ADVECTION – The horizontal transport of air or atmospheric properties. Commonly used with temperatures, i.e., “warm air advection”, or moisture, i.e., “moisture advection”.

ADVISORY- Issued for weather situations that cause significant inconveniences but do not meet warning criteria and, if caution is not exercised, could lead to life-threatening situations

AGL– above ground level.

AIR MASS – A large body of air having similar horizontal temperature and moisture characteristics.

ALERT– Automated Local Event Reporting in Real Time. Network of automatic raingauges that transmit via VHF radio link when precipitation occurs. Some sites are also equipped with other sensors such as temperature, wind, pressure, river stage or tide level.

ALBEDO -The percentage of light reflected by an object.

ALTOCUMULUS (AC) – Mid-altitude clouds with a cumuliform shape.

ALTOSTRATUS -Mid-altitude clouds with a flat sheet-like shape.

AMPLIFICATION: (AMPLFCTN)– Building, or sharpening, of an upper level high pressure ridge or low pressure trough.

ANABATIC – wind flowing up an incline, such as up a hillside; upslope wind.

ANEMOMETER– An instrument that measures wind speed.

ANGULAR MOMENTUM – the energy of motion of a spinning body or mass of air or water.

ANTICYCLONE– A large area of high pressure around which the winds blow clockwise in the Northern Hemisphere.

ARCTIC AIR – a mass of very cold, dry air that usually originates over the Arctic Ocean north of Canada and Alaska.

ARCTIC HIGH – a very cold high pressure that originates over the Arctic Ocean.

ASOS -Automated Surface Observing System. Observes sky conditions, temperature and dewpoint, wind direction and speed, and barometric pressure.

ATMOSPHERE – the mass of air surrounding the earth and bound to it more or less permanently by the earth’s gravitational attraction.

ATTM– AT The Moment

ATWC -Alaska Tsunami Warning Center, located in Palmer, AK.

AVALANCHE – a large mass of rapidly moving snow down a steep mountain slope.

AVHRR – Advanced Very High Resolution Radiometer. Main sensor on U.S. polar orbiting satellites.

AVN – Aviation Model generated every 12 hours by NCEP.

AWIPS – Advanced Weather Information Processing System. New NWS computer system integrating graphics, satellite and radar imagery.