METEOROLOGY FLIGHT PLANNING
FREEZING RAIN Rain that freezes upon impact and forms a glaze on the ground or exposed
FROZEN PRECIPITATION Any form of precipitation that reaches the ground in solid form
(snow, small hail and/or snow pellets, snow grains, hail, ice pellets, and ice crystals).
FUNNEL CLOUD A violent, rotating column of air which does not touch the ground, usually
appended to a cumulonimbus cloud (see tornado and waterspout).
GLAZE Ice formed by freezing precipitation covering the ground or exposed objects.
GRAUPEL Granular snow pellets, also called soft hail.
GUST Rapid fluctuations in wind speed with a variation of 10 knots or more between peaks
HAIL Precipitation in the form of small balls or other pieces of ice falling separately or frozen
together in irregular lumps.
HAZE A suspension in the air of extremely small, dry particles invisible to the naked eye and
sufficiently numerous to give the air an opalescent appearance.
HECTOPASCAL A unit of measure of atmospheric pressure equal to 100 newtons per square
meter, abbreviated hPa.
ICE CRYSTALS (DIAMOND DUST) A fall of unbranched (snow crystals are branched ice
crystals in the form of needles, columns, or plates.
ICE PELLETS (PL) Precipitation of transparent or translucent pellets of ice, which are round
or irregular, rarely conical, and which have a diameter of 0.2 inch (5 mm), or less. There are two
Hard grains of ice consisting of frozen raindrops, or largely melted and refrozen
b. Pellets of snow encased in a thin layer of ice which have formed from the freezing of either
droplets intercepted by the pellets or of water resulting from the partial melting of the pellets.
IN-CLOUD LIGHTNING (IC) Lightning which takes place within the thundercloud.
INDEFINITE CEILING The ceiling classification applied when the reported ceiling value
represents the vertical visibility upward into surface-based obscuration.
INSOLATION INcoming SOLar radiATION. The total amount of energy radiated by the Sun
that reaches the Earth's surface. Insolation is the primary source for all weather phenomena on