Australian Weather

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. 

18 Apr 2024, 3:20AM UTC

A weeklong stretch of low wind power was broken on Wednesday evening, as a weak cold front marched across southern Australia.  The chart below shows that the National Electricity Market (NEM) has endured a weeklong stretch of low wind generation, with wind power providing around 6% of the NEM’s electricity, down from last year’s average of 13.1% (Mon, April 15 to Wed, April 17).    The daily wind generation has been under 41 GWh/day for the last seven days leading up to Thursday, April 18. The calmest winds occurred on Sunday, April 14 with only 24 GWh/day produced or 4.6% of grid demand.   To put this in perspective, the average daily wind generation during the last year up to Wednesday, April 17, 2024, was 71 GWh/day, according to data from the open NEM.  This prolonged period of low wind was caused by blocking high pressure systems sitting over southern Australia, forcing cold fronts or strong wind further south.  The image below shows the Mean Sea Level Pressure chart on the calmest day, Sunday, April 14, with high pressure stubbornly sitting over the southern half of the country.  Image: Mean Sea Level Pressure Analysis at 4am AEST on Sunday, April 14. Source: Bureau of Meteorology.  As we mentioned earlier today, a positive Southern Annular Mode (SAM) has led to consistent high pressure systems positioned over latitudes well south of Australia during the first three months of the year and during this week. This has kept cold fronts south of the mainland, and even south of Tasmania.   READ MORE: WHAT IS THE SAM?   The period of light winds ended abruptly on Wednesday evening, with WattClarity reporting that wind production peaking above 3,000 MW at 9:10pm AEST.  The increased wind power on Wednesday night, was caused by a couple of factors;  A weak cold front swept across the southeast on Wednesday, bringing stronger winds.  A very shallow temperature inversion formed in the early evening protecting the surface from the stronger winds, but the wind turbine hub-height (150 metres above the ground) winds remained strong at around 28-38 km/h in SA.  Temperature inversions form at night when the ground cools quicker than the air above it, meaning that the temperature increases with height for a thin layer of the atmosphere.   During autumn, the temperature inversions are commonly shallow meaning that while the wind could be weak at the surface, the hub heights could continue to experience strong winds.  A similar phenomenon could happen again tonight across southern Australia, with another cold front passing across the south.  Looking ahead, light winds are expected to continue from Friday as a stubborn high-pressure system builds over the Bight until early to mid-next week.