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Rain & storms are increasing in NE SA, SE NT, SW QLD & western NSW & showers are scattering across northern VIC as instability increases. Showers are continuing along the eastern seaboard in persistent, moist onshore winds. A high is keeping much of the remainder dry.
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Today, 5:04AM UTC
Record-breaking global atmospheric moisture in April
Earth just had its most moisture-laden April on record as unrivalled air and ocean temperatures caused atmospheric moisture content to surge across the planet. It has been known since the 1800s that rising global air temperature allows Earth’s atmosphere to hold more moisture. This phenomenon is explained by the Clausius–Clapeyron relation, which shows that the atmosphere can hold about 7% more moisture for every 1°C of warming. It comes as little surprise then that record-breaking global air temperatures last month occurred alongside unprecedented atmospheric moisture. The amount of moisture in Earth’s atmosphere can be represented using a value called the ‘total column water’, which refers to the total amount of water in a vertical column of the atmosphere, including vapour, cloud water and cloud ice. This does not include the moisture that is present as precipitation (e.g. rain and snow). The global total column water last month was the highest on record for the month of April, beating the previous record from 2016. Image: Average global atmospheric moisture for April between 1940 and 2024, based on ERA5 data and processed by BenNollWeather April’s record-breaking atmospheric moisture was caused by unrivalled warmth in the atmosphere, which allowed the air to hold more water, and unprecedented global ocean temperatures, which enhanced evaporation. The map below shows the distribution of moisture in April 2024, with large areas of above average moisture in both the Southern and Northern Hemispheres. Image: Total column water anomaly for April 2024, based on ERA5 data and processed by BenNollWeather One area that had well above average atmospheric moisture in April was the state of Rio Grande do Sol in southern Brazil, which was hit by deadly floods in the first week of May. There are also a few regions of drier-than-average air on the map above, including central and western Australia. However, when averaged out across the globe, Earth’s atmosphere last month was wetter than any other April on record.
Today, 2:58AM UTC
Freezing ocean temps cold comfort for South Australians
No South Australian needs to be told that it has been desperately dry in recent months across most of the state, and especially in southern parts. "Adelaide is so dry my lawn is like brown dry paper that crunches when you walk on it... Where is our rain???" asked Weatherzone Facebook community member Mara Gemini on one of our recent posts. The answer to the question "Where is our rain?" is that it has been blocked by the unrelenting blocking high pressure systems which have been centred south of the mainland for the last month or more. These systems have prevented Southern Ocean cold fronts from surging northwards to South Australia on a regular basis and delivering much-needed autumn rain. And those strong highs have caused something else too: exceptionally cold water off the SA coastline. Source: BoM. Take a look at the chart above. It shows sea surface temperature anomalies in South Australian waters – or in other words, the current water temps compared to the average. As you can see, they are up to six degrees colder than usual for this time of year. Why is the ocean off SA so much colder than usual? As mentioned, it's all to do with those persistent highs. Because of their location south of the mainland, the highs have been consistently funnelling southeasterly winds in the direction of the SA coast. Because of a phenomenon called Ekman Transport, water moves at an angle of approximately 90 degrees to the left (in the S Hemisphere) of the prevailing wind. That means that water off the SA coast has been deflected out into the Southern Ocean When surface water is deflected away from the coast, it is replaced by an upwelling of colder water. And that explains the purple zone of super cold water around Ceduna and Streaky Bay in the image above. Image: Probably not the best week to take a dip along the Nullarbor coastline. Source: iStock. What do the unusually cold ocean waters mean for SA weather? Not good things, unfortunately. Cold fronts moving aross the ocean towards pick up more moisture from warmer waters and less moisture from colder waters. So when the fronts start arriving in southern SA more regularly this winter, rain-starved parts of southern SA can expect less rain than they'd see if sea surface temps were warmer. Without wanting to cause alarm, it's still worth noting that an upwelling of nutrient-rich cold water tends to attract fish, which in turn attarcts sharks. There are probably not too many swimmers or even surfers in the chilly SA waters right now, but it's still something to be aware of. Meanwhile the graph below shows the last 12 motnhs worth of rainfall in Adelaide. You can see how the taps basically turned off after January and unfortunately, there's no rain on the horizon over the next seven days.
08 May 2024, 6:46AM UTC
More rain for thirsty southwest WA
It won't be a deluge, but at least some rain is heading the way of the parched southwest corner of Western Australia from Friday into the weekend. Last week saw the first significant rainfall in the region for many months, with falls topping 100 mm at Wandering, an hour or so southeast of Perth, and more moderate falls elsewhere including 12 mm in Perth itself in the first three days of May. Another location where locals were extremely grateful to see last week's rain was Busselton, the gateway to the Margaret River wine and surf region, which had received a paltry 0.4 mm in the first four months of the year until 32.6 mm fell last week. But all of these areas need much, much more rain, and while the coming system won't deliver heavy falls of the type that are likely to arrive during the coming wet season, any rain will still be very welcome. READ MORE: Driest 12 months on record for big chunk of WA So how much rain will fall this week? Rain should arrive with a cold front on Friday. This is not a particularly strong system but we could still see up to 10 mm in Perth and slightly heavier falls further south – although falls are expected to be lighter once you get down towards Albany and the South Coastal forecast district. Indeed as shown in the image above of accumulated rainfall by Saturday morning, falls should be heaviest in the areas mentioned earlier – from about Perth to Busselton. Most of the rain should fall on Friday so if your weekend plans revolve around dry weather, you might just get lucky. Not that too many southwest WA locals would complain about an event being ruined by rain at the moment.
Weather in Business
07 May 2024, 11:23PM UTC
How severe thunderstorms impact energy infrastructure
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
Wind returning to southeastern Australia
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.
