Australian Weather

07 May 2024, 11:23PM UTC

Earlier this year destructive thunderstorms and winds equivalent to a category two cyclone lashed Victoria, bending towers and toppling trees and poles.  So, how can thunderstorms damage energy infrastructure, and are these events getting worse?   This event occurred during mid-February 2024, when a strong cold front generated severe thunderstorms and localised wind gusts of 130km/h after a prolonged period of extreme heat. The image below shows a squall line around 1,500km long causing lightning across four states in February.  Image: Himawari-9 satellite image, lightning and radar on Tuesday, February 13 at 3pm AEDT.  The destructive winds were caused by microbursts, which bent towers and toppled trees and poles in Vic, leaving thousands without power.   Image: Damaged transmission towers at Anakie, Source: AAP  Microbursts are a localised column of sinking air (downdraft) within a thunderstorm and is usually less than 4km wide. The cold, heavy air within this downdraft descends rapidly to the surface and then spreads out in all directions as it hits the ground. The image below shows how wind gusts are produced in thunderstorms.    Microbursts can be destructive and cause wind gusts above 100 km/h, which can be a risk for power infrastructure. The force applied to the structure is roughly proportional to the speed squared.  Fierce wind gusts from thunderstorms can:  Knock down trees, which can fall onto power lines  Topple poles  Knock out transmission towers.  Microbursts typically occur during the warmer months of the year and, unfortunately, they can develop rapidly and last for only a short period of time, making them difficult to predict and warn communities about.   Have these thunderstorm events become more severe in Victoria?   The severe thunderstorm season across southern Australia occurs during the warmer months of the year, between November and April.   While thunderstorms are more common across northern Australia, Qld, and NSW, they do occur frequently in the summer months. The map below shows the annual average lightning density in Vic between July 2014 and June 2023, with the most lightning occurring in the northeast high country each year.      Image: Weatherzone’s Total Lightning Network Annual lightning density mean between July 2014 and June 2023.  You can see in the map above that lightning is common to the north of Ballarat near Learmonth and Miners Rest, with the region seeing 37.7 pulses per year. The high country near Benalla and Whitfield recorded an average of 28.1 pulses, Thorpdale in Gippsland saw 24.5 pulses, and Melbourne only 8.2 pulses per year.    Research has shown that the warming climate is increasing the risk of heatwaves and bushfires, which can impact energy infrastructure. Unfortunately, it is unknown how global warming will affect thunderstorms and their associated destructive winds. To research climate change's impact on thunderstorms, we would need quality data that dates back well into history. Unfortunately, detecting lightning is a fairly new phenomena, so a solid climate base to compare data to is not currently existent.   According to the University of Melbourne researchers and Watt Clarity, ‘The evidence we do have suggests continued climate change may potentially increase the risk of extreme winds from thunderstorms. This is partly due to more moist and unstable air, which are essential for thunderstorms to form. We think these conditions could occur more often with climate change, in part because warmer air can hold more moisture.’   Indeed, much of Australia had an unusually stormy summer 2023/24, with Melbourne, Canberra and Brisbane all seeing 5 to 6 extra storm days a season. The map below shows that an unusually high number of thunder days were seen over most of Qld, NSW, SA, Vic, the ACT and Tas during the summer of 2023/24 compared to the average of the most recent nine years.  Image: Thunder day anomalies for summer 2023-24 versus the average thunder days for the nation’s nine most recent summers (2014/15 to 2022/23). 

23 Apr 2024, 12:07AM UTC

After a prolonged period of light winds, a surge of powerful winds and cool air will push through southeastern Australia during the next 48 hours.  As we wrote about last week the National Electricity Market (NEM) saw very low wind power generation during the seven days leading up to Thursday, April 18, with the daily wind generation having been under 41 GWh/day for this period.  Wind power has improved slightly during the past week, with wind power increasing for a few days over last weekend. The chart below shows that the winds across the NEM have already increased in response to a cold front approaching SA and Vic on Tuesday.  The increase in wind power is associated with a cold front sweeping across southeastern Australia, after a stubborn high-pressure system forced many cold fronts south for over a week.  The map below shows the cold front marching across the Bight, approaching SA on Tuesday morning. You can also see a broad area of speckled cloud in the Bight, which is a tell-tale sign that a large mass of cold polar air has broken away from the Antarctic region and is venturing into the relatively warm mid-latitudes.      Image: Himawari-9 satellite image at 9:30am AEST on Tuesday, April 23.  Northwesterly winds will continue to strengthen ahead of the cold front on Tuesday in SA and Vic before a strong southwesterly change hits Adelaide on Tuesday afternoon and Melbourne in the evening.   The images below show the wind gust forecast for Tuesday and Wednesday afternoon.      Image: Instantaneous wind gust forecast at 1pm AEST on Tuesday (top) (bottom)and Wednesday, April 23 and 24, according to ECMWF  While most of this wind should hit the wind power ‘sweet spot’, cut outs could occur at southeastern Vic and southern NSW wind farms late Tuesday into Wednesday. Generally, cut outs occur when wind speeds exceed 90km/h (25 m/s), which is when the wind turbines are turned off to prevent damage.  In the image above you can see the front and associated southerly change moving up the NSW coast on Wednesday, hitting Sydney on Wednesday afternoon.   Winds will then become light later this week as another high-pressure system moves into the Bight.   Cool change coming  Ahead of this change, much of southeastern Australia has experienced pleasant autumnal weather, with Sydney’s temperature for the next two days reaching 27°C. However, there will be a large temperature contrast ahead and behind the cold front in the next few days. The image below shows forecast air temperatures around 1.5km above sea level on Wednesday morning, showing the cool airmass moving over parts of SA, VIC, Tas.      Behind the cold front strong southwesterly winds will cause temperatures to plummet to around 2-3°C below average across southern Australia;  Melbourne and Adelaide's temperature dropping to around 16-18°C for several days following the front.   Hobart’s temperature will drop from 22°C on Tuesday to 15°C on Wednesday.   Sydney’s temperature will go from 5°C above average on Wednesday to average on Thursday.  The coolest air will move over Tas, bringing snow to the alpine region there.   Looking ahead, temperatures will recover later this week ahead of another cold front and burst of wind power early next week.