Bureau of Meteorology


The BOM Blog gives you the background and insider info on weather, climate, oceans, water and space weather—as well as the latest on the work of the Bureau.


We welcome participation in the comments section of our blog; however, we are not able to respond to all comments and questions and your comments may take a little time to appear. The blog is monitored from 9 am to 5 pm Monday–Friday.

Our community includes people of all ages and backgrounds and we want this to be a safe and respectful environment for all. To keep the discussion interesting and relevant, please:

  • respect other people and their opinions;
  • keep your comments on topic and succinct;
  • say why you disagree or agree with someone;
  • comment constructively—in a way that adds value to the discussion.

When commenting, please don't:

  • make defamatory, libellous, false or misleading comments;
  • use obscene, insulting, racist, sexist or otherwise discriminatory or offensive language;
  • post personal information about yourself or others, such as private addresses or phone numbers;
  • promote commercial interests;
  • violate the intellectual property rights of others;
  • violate any laws or regulations;
  • provoke others, distort facts or misrepresent the views of others; or
  • post multiple versions of the same view or make excessive postings on a particular issue.

We won’t publish comments that are not in line with these standards. Blocking/removal of content or banning of users is at our discretion.

There is no endorsement, implied or otherwise, by the Bureau of any material in the comments section. Users are fully responsible for the content they submit.

Commenting is available via a Facebook plugin, which can only be accessed by those with Facebook accounts.

You can contact us at bomblog@bom.gov.au.

Copyright | Disclaimer | Privacy


Contact our social media team at socialmedia@bom.gov.au

Cooking up a storm – how thunderstorms form

Cooking up a storm – how thunderstorms form

A thunderstorm is a form of turbulent weather accompanied by lightning and thunder. They are associated with a very tall cloud mass called a cumulonimbus cloud.

What causes thunderstorms?

Thunderstorms develop when warm, humid air near the ground receives an initial upward push from converging surface winds and rises rapidly in an unstable atmosphere. Thunderstorms can become severe when the atmosphere is particularly unstable and/or additional energy is drawn in from surrounding winds.

Storm photo

Thunderstorm in Esperance, Western Australia. Copyright: Jodie Midgley.

What is a severe thunderstorm?

While we experience many thunderstorms in Australia, more intense thunderstorms are referred to as severe thunderstorms. Severe thunderstorms can cause significant damage by wind gusts, large hail, tornadoes or flash flooding.

Thunderstorms which produce any of the following events are classified as severe in Australia:

  • hail of 2 cm diameter or more
  • wind gusts of 90 km/h or more
  • tornadoes
  • heavy rainfall that could cause flash flooding

Ingredients of a thunderstorm

The atmosphere needs 3 main ingredients to produce a thunderstorm.

  1. Moisture—sometimes indicated by low clouds or haziness in the morning or many cumulus clouds later (as shown in the image below)
  2. Atmospheric instability to make the atmosphere more buoyant
  3. A lifting mechanism such as heating or the approach of a front or low pressure trough.

Cloud photograph

A field of small cumulus clouds prior to strong convective development over the Apollo Bay coastline, Victoria. Copyright: Eleanor Joan Tralaggan.

Parts of a thunderstorm

Every thunderstorm cloud has several features, shown in the diagrams below.

  • Core: the part of the cloud where sustained strong updraughts of relatively warm and moist air condense to produce rain, hail and/or snow.
  • Flanking line: the dark flat cloud base that extends away from the core, usually to the west or north.
  • Anvil: a flat, often fibrous cloud sheet, above and usually ahead of the core.
  • Inflow-outflow region: the boundary between the warm air entering the thunderstorm and its cool outflow.

diagram of a thunderstorm

Diagram illustrating severe thunderstorm features.

Diagram showing a cross section of a tunderstorm.

Diagram showing a cross section of a tunderstorm.

Where and when do severe thunderstorms strike?

Severe thunderstorms can occur at any time of the year in Australia, although they are very rare during the dry winter months in the north. Most strike between September and March when the supply of solar energy is greatest. However severe winter storms linked to cold fronts are common in the south-west of Western Australia and south-east South Australia.

Comment. Tell us what you think of this article.

Share. Tell others.