Appendix A: Glossary of Selected Meteorological Terms -Cont.

APPENDIX A

AVIATION WEATHER

FUNNEL CLOUD A violent, rotating column of air, which does not touch the ground and

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 ten knots or more between peaks

and lulls.

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

main types:

Hard grains of ice consisting of frozen raindrops, or largely melted and refrozen

snowflakes.

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 thunder-cloud.

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 Sun radiated energy

reaching the Earth's surface. Insolation is the primary source for all weather phenomena on the

Earth.

INTENSITY QUALIFIER Intensity qualifiers are used to describe whether a phenomena is

light (), moderate (no symbol used), or heavy (+).

ISOBAR A line on a chart or diagram drawn through places or points having the same

barometric pressure. (Isobars are customarily drawn on weather charts to show the horizontal

A-4

Glossary of Selected Meteorological Terms