Thunderstorms

Thunderstorms develop in very unstable air and are produced by a cloud type called cumulonimbus. The lifecycle of a thunderstorm typically takes 1-3 hours although under some conditions, when severe storms are created, the event may last for 3-5 hours. These longer lasting storms are called “supercell” thunderstorms and are often particularly severe, capable of generating strong wind gusts, heavy rain, large hail and even tornados.

What is the difference between thunder and lightning?

Cumulonimbus clouds usually generate lightning, and lightning emits a noise that we call thunder – hence the term ‘thunderstorm’.

Lightning

Lightning is a massive electrical discharge that is generated within cumulonimbus clouds. Lightning can discharge between cloud and ground, cloud and cloud as well as within two different areas within a single cloud. A lightning discharge can generate up to 1 billion volts of electricity and explosively heat up the surrounding air to nearly 10,000°C or twice the temperature of the Sun’s surface.

Thunder

When lightning is discharged from a cloud during a thunderstorm the almost instantaneous heating of the air produces a shock wave in the air that travels outwards at the speed of sound and this is called thunder. The sound of thunder can travel considerable distances, depending on the existing atmospheric conditions but can often be heard out to 25 km from the lightning discharge.

What other elements of a thunderstorm are dangerous?

Hail

Hail is produced in cumulonimbus clouds when a liquid raindrop is carried above the freezing level by a thunderstorm updraft, after which it turns into a small pellet of ice. Eventually the hail will either become too heavy for the updrafts to support or be thrown clear of the updraft area. It will then fall to the ground in either small numbers or as a veritable “storm” of millions of hailstones. In supercell thunderstorms the hailstone may be circulated through the updraft area several times, growing untl it reaches very large dimmensions, sometimes of tennis ball size.

Tornadoes

A tornado is a violently rotating funnel of air that is usually associated with a super-cell thunderstorm. Tornadoes usually measure from 100 metres to 1 kilometre across and can generate surface winds upwards of 450 km/h. These are easily the highest surface winds encountered on the planet and can be tremendously destructive, capable of leveling even quite substantial buildings and they produce heavy loss of life around the world every year.

Downbursts

When thunderstorms reach their mature stage, downbursts are produced which can reach the ground as a massive wall of wind that spreads outwards in all directions from the base of the thunderstorm cloud. This wind surge across the surface is called a downburst, with a smaller scale version of 4 km or less referred to as a microburst.