Clusters of severe thunderstorms are expected to hit Australia’s southern regions on Thursday and Friday, posing a significant threat with intense conditions forecasted. The Bureau of Meteorology has issued severe weather warnings for widespread storm activity across South Australia, Victoria, and parts of Western Australia, New South Wales, and southern Queensland.
Some areas have already reported hail the size of golf balls and fierce winds. Severe thunderstorms, though often underestimated, can cause substantial damage. The infamous 1999 Sydney storm, for example, dropped 500,000 tonnes of hail, leading to one of Australia’s most expensive natural disasters at the time.
Such storms bring risks beyond just hail, including flash flooding, particularly when heavy rainfall is concentrated over a short period. Lightning, too, remains a constant threat. In 2016, supercell thunderstorms caused a statewide blackout in South Australia, toppling power towers and leading to widespread disruption. Just this year, storms knocked out power for thousands in Victoria after taking down several towers.
What Makes a Thunderstorm Severe?
Thunderstorms require certain conditions to form, primarily moisture in the air, atmospheric instability, and a trigger to lift warm air. However, severe thunderstorms are defined by the presence of “vertical wind shear,” where wind direction and speed change with altitude. This allows thunderstorms to grow more powerful, potentially leading to hail, damaging winds, tornadoes, or flash floods.
Supercells, a type of convective thunderstorm, are among the most dangerous. These storms have rotating updrafts, making them longer-lasting and more intense.
While forecasters can predict the likelihood of severe thunderstorms days in advance, pinpointing the exact timing and location remains challenging due to the complex nature of storm development.
Unusually Widespread Storms
The current storm system is unusual in its extensive reach, spanning from Kalbarri in central Western Australia to Victoria and beyond. The storms are driven by a large low-pressure system moving across the country. Moist air from the north, combined with atmospheric instability, is priming the system for thunderstorm activity.
As the low-pressure system forces air to rise, the energy stored in warm, moisture-laden air is released, fueling the development of severe thunderstorms. These rising air currents can travel several kilometers into the atmosphere, sometimes reaching the upper levels of the troposphere.
Severe thunderstorms are more common in southern Australia during spring and summer when moisture from the tropics combines with cold fronts from the south.
Tornadoes and Fire Risks
Severe thunderstorms can also trigger tornadoes, as seen in August when a tornado caused damage in northern Victoria. Although tornadoes are rare in Australia, the country experiences an estimated 30-80 each year, often spinning out of supercell thunderstorms. In 2013, a total of 69 tornadoes resulted in almost 150 injuries.
In addition, thunderstorms can exacerbate fire conditions by bringing strong, erratic winds, which can increase the spread of bushfires. Australia’s deadliest bushfire, Black Saturday in 2009, was fueled by intense northerly winds associated with thunderstorms, causing rapid firestorms.
Climate Change and Future Storms
As the planet warms, evaporation from warmer sea surfaces is increasing, adding more water vapor to the atmosphere. This can intensify rainfall during thunderstorms. However, the impact of climate change on other storm ingredients, such as wind shear and atmospheric instability, is less clear. Changes in circulation patterns could alter where and when severe storms occur, potentially bringing more intense thunderstorms to new regions and at different times of the year.
The next 48 hours will be critical as Australians prepare for what could be another dangerous bout of extreme weather.
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