Thunderstorms

Learn about types of thunderstorms in Australia, how they form and why they can be dangerous

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Thunderstorms and severe thunderstorms

How thunderstorms form

Types of thunderstorms

Thunderstorm phenomena

Thunderstorms and severe thunderstorms

A thunderstorm is any cloud system that produces thunder and lightning. They are made up of one or more cumulonimbus clouds – very tall, puffy, dark clouds that sometimes have a distinctive anvil-shaped top.

Thunderstorms – especially severe ones – can be among nature's most dramatic sound and light shows.

A typical thunderstorm lasts for about 30 minutes to an hour. Severe thunderstorms can last many hours and travel long distances.

In northern Australia, severe thunderstorms have different characteristics to those that typically happen in southern and central Australia. Find out more about severe thunderstorms in the tropics on our Tropical severe thunderstorms page.

Video: Ask the Bureau: What is a thunderstorm?

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Definition of severe thunderstorm

While we experience many types of thunderstorms in Australia, some more intense thunderstorms are referred to as severe thunderstorms.

A thunderstorm is classified as severe if it produces any of the following:

  • large hail – 2 cm in diameter or larger
  • damaging wind gusts – 90 km/h or greater
  • tornadoes
  • heavy rainfall that may lead to flash flooding.

If we expect a thunderstorm to produce any of these phenomena, we issue a severe thunderstorm warning. Most thunderstorms don't reach the intensity needed to produce these dangerous phenomena.

When and where severe thunderstorms hit

Severe thunderstorms can happen at any time of the year.

  • In Australia's north, they are less common during the dry season.
  • In the south, they are less common during winter months. However, severe winter storms linked to cold fronts are not uncommon.

Most severe thunderstorms happen between September and March when the supply of solar energy is greatest.

How thunderstorms form

Thunderstorms need 3 main ingredients to form:

  • moisture – moist, humid air that carries a lot of water vapour
  • atmospheric instability – a rapid decrease in temperature with height – to make the moist air more buoyant
  • a lifting mechanism, such as an approaching front or low pressure trough, to make the moist air rise rapidly.

Parts of a thunderstorm

Thunderstorm clouds, called cumulonimbus, have features including a:

  • core
  • inflow – warm and moist air flowing into the storm, providing the energy for the updraft
  • anvil – a flat, often fibrous cloud sheet, above and usually downwind of the updraft, mainly made up out of ice crystals
  • outflow – cool air flowing away from the storm, produced by evaporation of rain in the downdraft.
Diagram showing the key features of a thunderstorm cloud that rises about 12 m above the ground. The top of the cloud is in a v-shape and features a back-hanging anvil and overshooting top. Below the anvil, flanking line towers rise above a shelf cloud, which produces rain and hail. Light rain falls from the forward part of the anvil. Behind this, a wall cloud produces a tornado, while the back of the storm has a rain-free base.

Diagram showing some key features of a thunderstorm

Types of thunderstorms

There are 3 general thunderstorm types: single-cell, multi-cell and supercell. Each has a distinct structure, circulation pattern, and set of characteristics.

Single-cell thunderstorm

A single-cell thunderstorm's life cycle is limited to the growth and collapse of a single updraft pulse.

The cloud forms, grows to maturity and produces a heavy downpour. It then decays as the cool outflow spreads out and descending air cuts off the original warm inflow.

These thunderstorms are most likely to happen on summer afternoons and usually last no more than an hour. They can produce strong wind gusts (microbursts). Developing single-cell storms can produce waterspouts or (over land) weak tornadoes.

It's rare to encounter a pure single-cell storm – almost all of them have some multi-cell characteristics.

Multi-cell thunderstorm

Multi-cell thunderstorms are the most common. They consist of successive, separate updraft pulses that help maintain the system's overall strength, structure and appearance. The pulses may be:

  • very close together, so the thunderstorm is quite uniform over time, or
  • widely spaced, so the thunderstorm cycles repeatedly through stronger and weaker phases.

Multi-cells can produce any of the thunderstorm phenomena but are less commonly associated with tornadoes or giant hail.

Supercell thunderstorm

This type of thunderstorm is very strong and can produce:

  • damaging and destructive wind gusts
  • heavy rainfall
  • tornadoes
  • large to giant hail.

They can last a long time, maintaining an almost steady state for many hours.

A supercell is distinguished by a deep and rotating updraft called a mesocyclone – a vortex within the thunderstorm.

Video: Ask the Bureau: What is a severe thunderstorm?

View video transcript

Thunderstorm phenomena

Thunderstorms can bring a range of phenomena – heavy rain, thunder and lightning, hail, wind gusts and even tornadoes.

Thunder and lightning

Lightning is electrical discharge. It happens when there are large voltage differences between:

  • the ground and part of the storm, or
  • between parts of the storm.

The difference in voltage needs to be several million volts. That is, large enough to overcome the insulating effect of the air.

Lightning strikes can happen within the cloud, between clouds, or between clouds and the ground.

Thunder is the sound produced by the explosive expansion of air heated by the lightning strike to temperatures as high as 30,000 °C.

To see the annual variation in thunderstorm and lightning activity across Australia, view the average annual thunder day and lightning flash density maps.

Hail

Hail is solid precipitation, in the form of balls or pieces of ice known as hailstones.

Hailstones can form in a thunderstorm with a strong updraft. This happens when small particles of snow with a thin crust of ice (called graupel) are suspended in the updraft. They can grow rapidly by 'sweeping up' small cloud droplets which freeze onto the surface of the graupel.

Hailstone diameter can range from 5 mm to more than 100 mm (10 cm), but most are smaller than 25 mm. Hailstones larger than lawn bowls have been recorded in Australia. For example, a hailstone with a maximum diameter of 133 mm (13.3 cm) was recorded during a hailstorm in Brisbane on 31 October 2020.

Damage from hailstones may include:

  • crop damage from small hail stones (less than 20 mm diameter)
  • vehicle damage from larger hailstones (more than 20 mm diameter)
  • widespread damage from giant hailstones (greater than 50 mm diameter).
Photo of 4 giant hailstones sit next to a tape measure, showing that they are more than 5 cm in diameter.

Giant hailstones measuring 5 cm across

Wind gusts

In a mature thunderstorm, the falling rain and hail drag the surrounding air downwards. Evaporation from the raindrops and melting ice cool the nearby air. This creates a cold dense bubble of air that speeds down towards the ground.

When it reaches the ground, this downdraft creates a dome of cool air. It can spread sideways very quickly, producing a cool, gusty wind that can cause damage.

The downdraft can be enhanced when there are strong winds in the lowest 2 km of the atmosphere above Earth's surface.

Tornadoes

Tornadoes do happen in Australia and have caused significant damage.

They are the rarest and most violent of thunderstorm phenomena. Learn more about Tornadoes.

 

Severe weather warnings

View the National warnings summary.