Glossary of Weather Phenomena

This glossary describes the weather phenomena reported by Truganina Weather, if and when observed.


Lightning is caused by electrical discharge in a Cumulonimbus (thunder) cloud. The electrical discharge, which may either be cloud-to-cloud, cloud-to-air or cloud-to-ground, produces intense heating of the air that ultimately results in an audible shockwave, which we call thunder.

Lightning and thunder will always occur together, however if lightning is seen but thunder is not heard it is usually because the thunder is more than 20 km away.


Thunder is caused by the intense heating of the air in a lightning strike. The heated air rapidly expands into the surrounding cooler air creating an audible shockwave, which we call thunder.

Thunder and lightning will always occur together, however if thunder is heard but lightning is not seen it is likely that the lightning is cloud-to-cloud and hidden from view.


Hail is solid precipitation in the form of pieces of ice that falls from Cumulonimbus (thunder) clouds. Water droplets are continuously moving up and down though the cloud and freeze when they get to the top of the cloud where it is very cold. Once formed, the hailstones are in constant motion due to the updraughts and continue to grow as they become coated with more layers of ice. Eventually the weight of the hailstones will become too great for the updraughts and they fall to earth.


Fog is caused by tiny water droplets suspended in the air near the ground, reducing visibility to less than 1,000 m. Radiation fog is the most common of the four types of fog and usually occurs in winter, aided by clear skies and calm conditions. The cooling of the land overnight by thermal radiation cools the air close to the surface. This reduces the ability of the air to hold moisture, allowing condensation and fog to occur. Radiation fog usually dissipates soon after sunrise as the ground warms.


Frost is normally formed on still, clear and cold nights. The cool air causes water vapour in the air to condense and form droplets on the ground. When the temperature of the ground or surface is below 0° C the moisture freezes into ice crystals.

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