Appendix A: Glossary of Selected Meteorological Terms -Cont.

AVIATION WEATHER

APPENDIX A

distribution of atmospheric pressure reduced to sea level or the pressure at some specified

altitude.)

ISOTACH A line joining points of equal wind speed.

ISOTHERM A line on a chart or diagram drawn through places or points having equal

temperature.

LOW DRIFTING A descriptor, DR, used to describe snow, sand, or dust raised to a height of

less than six feet above the ground.

LOW DRIFTING DUST Dust raised by the wind to less than six feet above the ground;

visibility is not reduced below seven statute miles at eye level, although objects below this level

may be veiled or hidden by the particles moving nearly horizontal to the ground.

LOW DRIFTING SAND Sand raised by the wind to less than six feet above the ground;

visibility is not reduced below seven statute miles at eye level, although objects below this level

may be veiled or hidden by the particles moving nearly horizontal to the ground.

LOW DRIFTING SNOW Snow raised by the wind to less than six feet above the ground;

visibility is not reduced below seven statute miles at eye level, although objects below this level

may be veiled or hidden by the particles moving nearly horizontal to the ground.

MANUAL STATION A station, with or without an automated surface weather observing

system, where the certified observers are totally responsible for all transmitted meteorological

reports.

METAR/SPECI An evaluation of select weather elements from a point or points on or near the

ground according to a set of procedures. It may include type of report, station identifier, date and

time of report, a report modifier, wind, visibility, runway visual range, weather and obstructions

to vision, sky condition, temperature and dew point, altimeter setting, and remarks.

MILLIBAR (Bar a unit of pressure equal to 1,000,000 dynes per square centimeter.) A

millibar is equal to 1/1,000 of a bar.

MIST A hydrometer consisting of an aggregate of microscopic and more-or-less hygroscopic

water droplets or ice crystals suspended in the atmosphere that reduces visibility to less than six

statute miles but greater than or equal to 5/8 statute mile.

MOIST ADIABATIC LAPSE RATE See Saturated Adiabatic Lapse Rate.

NON-UNIFORM SKY CONDITION A localized sky condition varying from that reported in

the body of the report.

NON-UNIFORM VISIBILITY A localized visibility varying from that reported in the body of

the report.

Glossary of Selected Meteorological Terms A-5