Why storms happen in summer

How are storms formed?

Thunderstorms need three main ingredients from the atmosphere to form, according to the Bureau of Meteorology:

• moisture from humid air carrying water vapour 

• atmospheric instability to make the moist air more buoyant

• a lifting mechanism like heat, a low-pressure trough or an approaching front to make the moist air rise rapidly.

When the warm, moist air is thrown upwards in an ‘updraught pulse’ (also called a ‘convection cell’), a cloud forms and produces a heavy downpour of rain. Single-cell thunderstorms only experience one updraught pulse are generally short weather events, while multicell thunderstorms have multiple updraught pulses that maintain the storm over time. Supercell thunderstorms have a large, continuous updraught that allows the thunderstorm to grow in size and severity for many hours.

Storms require moisture, buoyancy and lift. Image: Matt Harvey

What are severe thunderstorms?

Intense, violent thunderstorms are classified as severe thunderstorms. They are formed when the atmosphere is particularly unstable, or when surrounding winds deliver additional energy to the storm.

In Australia, a thunderstorm is classified by the Bureau of Meteorology as a severe thunderstorm when it produces any of the following:

• heavy rainfall that could cause flash flooding

• wind gusts of 90km/h or more

• hail of 2cm diameter or more

• tornadoes

Severe thunderstorms are a threat to Australian property and safety due to their ability to cause significant damage.

Severe thunderstorms can cause flash flooding and other dangers. Image: Getty

Why are storms more common in summer?

The Bureau of Mereology reports that severe thunderstorms strike mostly between September and March.

That’s because summer has longer sunlight hours and warmer temperatures to heat the air above the ground. Summer also has higher humidity than other seasons: according to the Climate Council, for every degree of warming, the atmosphere can hold about 7 per cent more moisture. As a result, summer sees lots of warm, moist air rising into the atmosphere, where they brew into storms.

If Australia experiences a La Niña or negative Indian Ocean Dipole weather event, the atmosphere becomes even more unstable, leading to wetter and stormier weather.

Australian summers induce more thunderstorms thanks to their prevalent humid air. Image: Getty

How can I prepare for storm season?

The best way to stay safe this summer storm season is to learn how to manage stormy weather.

On the road

You can also refresh on how to drive safely in wet and stormy conditions, remembering to never drive through flood waters.

In the home

By staying tuned to weather updates from reputable sources like the Bureau of Meteorology, you can prepare ahead of time to protect your home from floods or protect your car from hail damage.

Have plans in place for how to deal with a blackout, especially if you don’t have solar batteries with a blackout mode. Finally, make sure your home insurance policy is up to date by completing a home inventory and updating your policy.

Severe thunderstorms strike mostly between September and March. Image: Getty

On holiday

If you’re going on holiday this storm season, ask a neighbour or family friend to check your property before a storm. They may be able to help secure your house, such as by tying down loose objects in the yard, and moving your car undercover.

Health and wellness

Storm season introduces thunderstorm asthma: asthma attacks triggered by pollen grains absorbing moisture during a storm. These pollen grains burst into smaller fragments, get dispersed by the wind, and then pass into your lungs, causing major health risks.

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