Long-range weather prediction failure

What’s happened to the El Niño that experts warned earlier could mean warmer and drier weather and increased bushfire risk for much of Australia this summer? The Australian Bureau of Meteorology (BOM) declared the El Niño in September 2023, three months after US weather agency NOAA and two months after the UN’s World Meteorological Agency. The El Nino weather cycle is often linked to hotter and drier springs and summers for Australia, but the torrential and damaging storms and floods on the east coast in recent weeks have been anything but dry.

However, the BOM has defended its long-range forecasting after a predicted hot and dry summer turned into widespread rain and flooding.

Summer weather predictions

On 19 September the BOM said (Appendix A):
– “Warmer and drier conditions will be more likely over spring (September – November) and summer (December – February) for parts of Australia”.
– “An established El Niño and positive Indian Ocean Dipole (IOD) reinforces our confidence in those predictions. Based on history, it is now also more likely that warm and dry conditions will persist over eastern Australia until autumn.”

On 30 November the BOM said (Appendix B):
– “a high chance of warmer than usual days and nights across Australia, below average rainfall likely for much of the tropics and Western Australia, and an average rainfall for the rest of the continent.”
– “El Niño is predicted to continue over summer when its influence varies across the continent.”
– “El Niño is typically associated with a drier than average wet season in parts of Australia’s tropical north while its influence on rainfall over southern parts of Australia wanes over summer”. It was expected to be drier than usual because of an El Niño weather cycle.

So, the prediction for the eastern Australia in summer was:
– Below average rainfall / drier that normal (made three months before mid-summer).
– Average rainfall (made one month before mid-summer).

In early December 2024, the following prediction was made for summer (King and Dowdy, 2023). “We usually see fewer tropical cyclones during El Niño summers, noting that tropical cyclones can cause extreme rainfall in northern Australia. The seasonal outlook reflects this, with an 80% chance of a below-average number of tropical cyclones.” So, they still predicted below-average rainfall.

Actual summer weather

Northern Queensland was flooded in December 2023 by tropical Cyclone Jasper. Inland Queensland was flooded in January 2024 by tropical Cyclone Kirilly, which also flooded NSW in February 2024 (Appendix C). South-east Queensland was flooded in December 2023 and January 2024. And regional Victoria was flooded in December 2023. Many parts of Victoria and South Australia have recorded an entire summer’s worth of rainfall already, and others face flooding emergencies.

For thousands of people around Australia the Christmas of 2023 will be remembered not as a season of joy and goodwill, but for torrential storms and flash floods that claimed lives and tore through homes. At least seven people died in storms in Queensland and Victoria from flood waters and falling debris, and three more were lost from a yacht in Brisbane’s Moreton Bay.

The ongoing rains are making a mockery of spring headlines of dangerous bushfires and water shortages and have set the pattern for Australia to record a wetter than normal summer. Victoria has just experienced its wettest start to a year since records began early last century, New South Wales has been lashed by phenomenally heavy rainfall and Queensland’s rainfall average during December was 22% above the mean range.

The actual October to December 2023 rainfall in eastern Australia was generally above average, whereas it was predicted to be below average.

According to the BOM the rainfall in December 2023:
– was above average for much of northern, eastern and south-western Queensland, most of Victoria and South Australia, parts of southern New South Wales, and areas in south-eastern Western Australia and the western Top End in the Northern Territory,.and
–  was below average for large parts of western and northern Western Australia, Northern Territory and north-western Queensland, and for an area of western New South Wales extending into eastern South Australia.

So, the 3-month ahead forecast of drier weather this summer was totally wrong and the one month ahead forecast of average rainfall was wrong in eastern Australia, including the tropics.

In January 2004 the BOM did a new forecast for January to March 2024. It had above median rainfall in parts of south-east Queensland, eastern NSW and Victoria. “Neutral rainfall” over the interior and southern parts of the country. And drier than average conditions for most of WA, parts of the NT and some parts of Queensland.

But Tully in north Queensland flooded when it recorded 458 millimetres overnight on 23-24 February 2024. And some weather stations in the area recorded the highest levels of rainfall in 25 years.

Discussion

The BOM forecasted warmer temperatures than usual and less rainfall than usual for this summer (2023-24). However, many areas have received more rainfall than usual, which shows how difficult it is to predict the weather 1-3 months ahead (Appendix D).

South Australian Cattle Company Managing Director Tim Burvill says the BOM has “lost all credibility in the farming industry” as a result of their inaccurate weather forecasts. 2023 was a disastrous year for anyone in agriculture, particularly livestock. The BOM continually told farmers there would be a hot and dry year. Then its “dry summer” predictions turned into an absolute washout when it started raining in November and it hasn’t stopped since. And the BOM’s predictions about cyclone Jasper in December 2023 were just diabolical.

We have seen previously that cyclone Jasper showed that the atmosphere is more complicated than the mathematical models used to make weather predictions. These models failed to predict the torrential rainfall associated with the trajectory of Jasper across northern Queensland.

El Nino years generally bring above-average temperatures in Australia and a relatively dry weather. A study of spring rainfall concluded that “one should not expect dry conditions in La Niña or wet in El Niño for eastern Australia” (Tozer et al, 2023). So having so much rainfall in an El Nino phase was exceptional. The fact that eastern Australia experienced floods in the El Nino of summer of 2023-24, indicated that weather systems are more compacted that we think!

One of the likely reasons for this enhanced summer rainfall — particularly over the south-eastern states — has been a positive Southern Annular Mode (SAM). But a persistent positive SAM is usually associated with a La Nina, and not an El Nino. Also, the Madden-Julian Oscillation (MJO) is currently encouraging wet conditions across northern Australia. However, this explanation was given after the rains and floods occurred! That’s a hindcast, not a forecast! So they seem to pick the weather cycle that supports their narrative – the ENSO, the IOD, the SAM or the MJO! It was ENSO and IOD for the forecast and SAM and MJO for the hindcast!

The BOM provides daily weather forecasts up to seven days ahead, which are more unreliable with increased time. And Meteologix enables comparisons between different weather models (Appendix E). Accurate forecasts of indices like the SAM and the MJO are limited to a few weeks ahead. And due to the complex nature of the atmosphere, it is impossible to accurately predict specific weather events beyond the next week or so. So, weather forecasts more than a few weeks ahead have poor accuracy. This is consistent with the fact that seasonal forecasts (1-3 months ahead) can have very poor accuracy as we have seen this summer.

A news article blamed sensationalist news media and social media for driving fear and anxiety about the summer weather. But we have looked at the BOM forecasts in this post. The BOM has claimed that “By and large, for the past five months our long-term forecasts have about a 65% accuracy for rainfall and 98% accuracy for temperature. And that’s the best that you’ll find anywhere in the world.” But an atmospheric science researcher stated, “When they issue the one-month rainfall forecast, take it with a grain of salt (it is likely to be untrue or incorrect) and when there’s a three-month forecast, take it with a cup of salt (it has even lower accuracy)!”

Our atmosphere and oceans do not behave in simple, easily predictable ways. They are non-linear, chaotic systems. That’s why all forecasts are given as a probability, not a certainty.

Conclusion

So, the 3-month ahead rainfall forecast for this summer was totally wrong and the one month ahead forecast was wrong in eastern Australia, including the tropics. This illustrates that the complexity of weather systems makes it difficult to predict seasonal rainfall. Of course, it is impossible to forecast weather over a 30-year period.

As climate is weather over a 30-year period, it’s impossible to predict the future climate with the certainty that is often claimed today.

Appendix A: BOM Media release of 19 September 2023

The Bureau of Meteorology (BOM) has declared that El Niño and a positive Indian Ocean Dipole (IOD) are underway.

Warmer and drier conditions will be more likely over spring and summer for parts of Australia, under the influence of these two climate drivers.

BOM Climate Manager Dr Karl Braganza said both El Niño and a positive Indian Ocean Dipole (IOD) tend to draw rain away from Australia.

“Over spring, their combined impact can increase the chance of below average rainfall over much of the continent and higher temperatures across the southern two-thirds of the country,” Dr Braganza said.

“The Bureau’s three-month forecast for Australian rainfall and temperature have been indicating warm and dry conditions for some time.”

“An established El Niño and positive IOD reinforces our confidence in those predictions. Based on history, it is now also more likely that warm and dry conditions will persist over eastern Australia until autumn.”

El Niño events increase the risk of extreme temperature shifts, like heatwaves and hotter days.

Increased fire danger in south-eastern Australia is associated with El Niño conditions. A positive IOD contributes to greater fire risk over southeast Australia in spring, while El Niño contributes to elevated fire risk over both spring and summer.

The Bureau made the El Niño declaration after three of the four El Niño criteria were met, including a sustained response in the atmospheric circulation above the tropical Pacific.

The last time Australia encountered both El Niño and a positive IOD was in 2015.

“Around two-thirds of Australia’s driest years on record were during El Niño however, no two El Niño or IOD events or their impacts are the same,” Dr Braganza said.

“El Niño is part of a natural climate cycle that affects global weather and occurs on average every three to five years.”

Bureau Senior Climatologist Catherine Ganter said the Indian Ocean Dipole can have as large an influence on Australia’s rainfall and temperature as El Niño.

“A positive IOD often results in below average rainfall during spring for much of central and southern Australia and warmer than average maximum temperatures for the southern two-thirds of Australia,” Ms Ganter said.

“Similar to El Niño, the IOD describes a natural climate cycle brought about by sustained changes in the difference between sea surface temperatures in the tropical western and eastern Indian Ocean.”

Since 1960, when reliable records began for the IOD, there have been around 16 positive IOD and 15 El Niño years. Seven years have seen positive IOD and El Niño events happen at the same time.

Appendix B: BOM Media release of 30 November 2023

The Bureau’s summer long-range forecast shows a high chance of warmer than usual days and nights across Australia, below average rainfall likely for much of the tropics and Western Australia, and a more neutral rainfall signal for the rest of the continent.

After a drier than usual spring and winter for much of Australia, the more neutral summer rainfall forecast outside of the tropics may mean summer rainfall is closer to average for those areas.

Bureau of Meteorology National Manager Climate Services Dr Karl Braganza said our forecasts leading into summer started to suggest the chance of average rainfall for large areas of eastern Australia.

“The forecasts suggested the chance of average rainfall for parts of the east towards the end of spring and early summer, and we have seen some decent rainfall in November to finish off the spring season,” he said.

“Compared to outlooks issued mid-year, the dry signal has continued to ease across the eastern half of the continent outside of the tropics.”

But Dr Karl Braganza noted that summer is typically a drier time of year across the southern half of the continent and Western Australia has continued to see very dry conditions throughout spring, with no relieving rains.

This summer there’s an increased risk of:
– extreme heat
– heatwaves
– bushfire weather, and
– marine heatwaves

Most of the continent has an increased chance of unusually high temperatures possibly in the top 20% of records for this time of year.

El Niño is predicted to continue over summer when its influence varies across the continent.

“El Niño is typically associated with a drier than average wet season in parts of Australia’s tropical north while its influence on rainfall over southern parts of Australia wanes over summer,” Dr Braganza said.

Dr Braganza said the dry and warm conditions over much of spring along with the warm summer forecast were still contributing to an elevated fire risk this summer, and we have already seen significant fire activity across Australia, and more recently significant impacts in Western Australia.

“This summer all communities across Australia are urged to prepare for bushfire and monitor local conditions.”

Despite the widespread storms in the second half of November Australia’s overall spring rainfall is tracking to be around 23% below average.

Much of Australia has experienced a drier and warmer spring than usual, which is typical of El Niño and positive Indian Ocean Dipole events.

Appendix C: Ex-tropical cyclone Kirrily brings heavy rain to NSW (6 February 2024)

After spending 10 days flooding much of Queensland, Kirrily crossed the border into NSW on Monday triggering a warning for flash flooding for nearly half the state and a flood watch for 12 rivers. The near record high rain is due to Kirrily’s unusual southern track and strength — a rare weather pattern for NSW where the amount of moisture in the atmosphere is at levels normally confined to the Australian tropics.

100mm at Fort Grey near the border was nearly double its summer average and the locations heaviest rain in 40 years. Tibooburra recorded 79mm, the town’s heaviest rain in three years and heaviest February fall in 27 years. White Cliffs had seen in excess of 80mm — the town’s heaviest fall in 31 years. Condobolin received 79mm — heaviest February rain in 55 years.

And Warragamba Dam could reach capacity this week after a wet November to January – up to 200% of the long-term average across the catchment. The news of Sydney’s main water supply approaching capacity comes just months after Sydney Water advised residents to conserve water!

“Drought in Australia is cyclic and inevitable, and recent advice indicates we are moving into a phase where rain is expected to hit historic lows over the next 12 months,” Sydney Water managing director Roch Cheroux said in October 2023. What a poor forecast it turned out to be!

Appendix D: Summer rainfall 2023-24

The BOM reported that summer rainfall in 2023-24 was 18.9% above the 1961–1990 average for Australia as a whole. Summer rainfall was above average for large parts of the eastern two-thirds of the mainland – in some areas it was very much above average (in the highest 10% of all summers since 1900). But areas in western and central Western Australia, southern Northern Territory and Tasmania had a drier than average summer.

Significant flooding, associated with tropical systems, affected large areas of northern Australia during summer, while severe thunderstorm activity brought extensive flooding to parts of the eastern and south-eastern mainland.

Queensland’s summer’s rainfall average of 421.9mm was 30% above the 1961-1990 average for the state. Whyanbeel Valley in North Queensland recorded the most rain in nearly 50 years with 3,323mm. And a 54-year-old rainfall record was broken when 714mm fell in Mossman over 24 hours on 18 December.

Appendix E: Meteologix statement on weather forecasting

Meteologix is a Swiss weather forecasting service that allows users to compare different weather models for their location. You can see how various models align or differ in their predictions, which can be helpful for understanding weather patterns. They state:

“Some Weather Services pretend that you can know in the morning where exactly a storm will happen in the afternoon. Or if it will be 10 deg C or 21 deg C (50 deg F or 70 deg F) 20 days from now. The truth is: they can’t. Actually, nobody can. With all those Apps out there pretending a knowledge which doesn’t exist in meteorological science, people get frustrated about those weatherpersons. They give us a forecast for our place 2 weeks away, how can they be wrong for the next day?

With meteologix.com, you can check out what we know and what we don’t. You can compare the results of the different weather models for your place and see in the forecast XL if the different model outputs have the same idea for day 8 or it’s a mess between winter and summer for the same day. If so, you know, that you (and the meteorologists) know nothing.”

References

This post was inspired by:
Experts warned El Niño was likely to bring Australia a hot, dry summer. What happened?, 3 January 2024.

BOM defends El Nino forecast after widespread criticism, 15 January 2024
King, A and Dowdy A, We’re in an El Niño – so why has Australia been so wet?, 4 December 2023
Tozer CR et al, 2023, “Impacts of ENSO on Australian rainfall: what not to expect”, J. Southern Hemisphere Earth Systems Science, 73(1), 77-81.

Written, January 2024

Also see: Can we change the climate?