Appendix A: Glossary of Selected Meteorological Terms -Cont.

APPENDIX A

AVIATION WEATHER

SMOKE A suspension in the air of small particles produced by combustion. A transition to

haze may occur when smoke particles have traveled great distances (25 to 100 statute miles or

more) and when the larger particles have settled out and the remaining particles have become

widely scattered through the atmosphere.

SNOW Precipitation of snow crystals, mostly branched in the form of six-pointed starts; for

automated stations, any form of frozen precipitation other than hail.

SNOW GRAINS Precipitation of very small, white opaque grains of ice; the solid equivalent

of drizzle.

SNOW PELLETS Precipitation of white, opaque grains of ice. The grains are round or

sometimes conical. Diameters range from about 0.08 to 0.2 inch (2 to 5 mm).

SPRAY An ensemble of water droplets torn by the wind from an extensive body of water,

generally from the crests of waves, and carried up into the air in such quantities that it reduces

the horizontal visibility.

SPECI A surface weather report taken to record a change in weather conditions meeting

specified criteria or is otherwise considered to be significant.

SQUALL A strong wind characterized by a sudden onset in which wind speeds increase to at

least 16 knots and are sustained at 22 knots or more for at least one minute.

STANDARD ATMOSPHERE A hypothetical vertical distribution of the atmospheric

temperature, pressure, and density, which by international agreement is considered to be

representative of the atmosphere for pressure-altimeter calibrations and other purposes

(29.92 in-Hg or 1013 Pa).

STANDING LENTICULAR CLOUD A more or less isolated cloud with sharp outlines

generally in the form of a smooth lens or almond. These clouds often form on the lee side of and

generally parallel to mountain ranges. Depending on their height above the surface, they may be

reported as stratocumulus standing lenticular cloud (SCSL), altocumulus standing lenticular

(ACSL), or cirrocumulus standing lenticular cloud (CCSL).

STATION ELEVATION The officially designated height above sea level to which station

pressure pertains. It is generally the same as field elevation at an airport station.

STATION IDENTIFIER A four-alphabetic-character code group used to identify the observing

location.

STATION PRESSURE Atmospheric pressure computed for the level of the station elevation.

SUMMATION LAYER AMOUNT A categorization of the amount of sky cover at and below

each reported layer of cloud.

A-8

Glossary of Selected Meteorological Terms