METEOROLOGY FLIGHT PLANNING
SHOWER(S) A descriptor, SH, used to qualify precipitation characterized by the suddenness
with which they start and stop, by the rapid changes of intensity, and usually by rapid changes in
the appearance of the sky.
SIGNIFICANT CLOUDS Cumulonimbus, cumulonimbus mammatus, towering cumulus,
altocumulus castellanus, and standing lenticular or rotor clouds.
SKY CONDITION The state of the sky in terms of such parameters as sky cover, layers and
associated heights, ceiling, and cloud types.
SKY COVER The amount of the sky, which is covered by clouds or partial obscurations in
contact with the surface.
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
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 (two to five 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 that meets
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).