Thunderstorms require 3 ingredients to occur, and without 1 of these 3 ingredients it is very difficult (borderline impossible) for storms to occur. The 3 ingredients are instability, moisture and a trigger.
What we refer to as a trigger, is something that can ‘trigger’ a storm. This is typically in the form of a trough or frontal system (i.e cold front) – this allows the warmer air at the surface to be lifted into the atmosphere where it can produce cumulus clouds, leading to storms. Instability occurs when the temperatures in the troposphere are put under a rapid change – thus making the atmosphere unstable. Moisture comes in off the ocean, and this is required so the atmosphere can produce ice crystals which later fall as rain/hail.
There are 3 types of storms, all of which occur over South-East Queensland.
Orographic Thunderstorm: This occurs from air being forced up by a mountain or hillside (i.e Great Dividing Range)
Air Mass Thunderstorm: This occurs from localised convection in an unstable environment
Frontal Thunderstorms: These occur along the boundaries of weather fronts
These thunderstorms can become severe, and that occurs when the updrafts in the thunderstorm (air rising within the storm) become strong enough. Not all thunderstorms do become severe, as it requires much more energy, instability and moisture than regular storms. However, when they do they pose a risk of:
Heavy to Very Heavy Rain which may result in Flash Flooding
Frequent/Dangerous Cloud-to-Ground Lightning
There is another type of severe storm which occurs, and that is called a Supercell. Supercells develop when the updrafts within the storm become balanced with the downdrafts, and this develops perfect unity within the storm. Supercells pose more risk than typical severe storms, these include:
Large to Very Large Hail (anywhere from Tennis Balls to Bowling Balls)
Damaging to Destructive Winds (highest gust ever recorded in Australia was 196km/h)
Thunderstorms can occur in any month of the year, however they are more typical over the Spring and Summer months when heat and moisture are at their peak across Australia and in particular South-East Queensland/North-East New South Wales.