This year’s Australian snow season could be influenced by a very strong El Niño, increasing the likelihood of below-average snow in the Australian Alps.

The Pacific Ocean is currently in a neutral phase, meaning neither El Niño nor La Niña are in place. However, an El Niño pattern is emerging, and forecast models predict that El Niño will become established this winter and may last through the second half of the year.

Some forecast models, including the Bureau of Meteorology’s ACCESS-S2 model, predict that the impending El Niño will become very strong, meaning sea surface temperature anomalies in the central tropical Pacific Ocean will reach more than 2°C above the long-term average. Some forecasters and researchers refer to a very strong El Niño as a ‘super’ El Niño, however this is not a term officially used by the Bureau of Meteorology.

While a stronger El Niño does not guarantee that it will have a strong influence on Australia’s weather, the most recent ‘super’ El Niño years have all had a similar effect on the Australian snow season – they usually cause less snow.

How does a very strong El Niño affect the Australian snow season?

The most recent very strong El Niño events occurred in 2015-16, 1997-98, 1982-83 and 1972-73. The three most recent of these events were associated with below-average snow in the Australian Alps during the year El Niño became established.

According to snow depth data from Spencers Creek in NSW, which sits at about 1830 metres above sea level, the long-term average season peak snow depth is around 196 cm. During the last three very strong El Niño formation years, the peak snow depth only reached 91 to 150 cm. In 1972, the snow depth was slightly above average.

Image: Season peak snow depths at Spencers Creek NSW, with very strong or ‘super’ El Niño years highlighted in red. Source: Weatherzone.

The graph above shows that most, but not all, very strong El Niño years since 1954 have been associated with below average snow at Spencers Creek in NSW. This shows that while very strong El Niño years make below average peak snow depths more likely, the Australian Alps can still see good snow due to natural variability.

El Niño makes snow less likely in Australia by reducing rainfall and cloud cover and increasing average maximum temperatures in the country's southeast, including the Alps. This influence is amplified when the El Niño coincides with a positive Indian Ocean Dipole (IOD). On average, the season peak snow depth at Spencers Creek is about 35 cm lower during El Niño years. The two lowest years on record were also El Niño years – in 1982 and 2006 – despite 2006 only being a weak El Niño year.

Climate change and Australian snow

In addition to climate drivers like El Niño and the IOD, the background influence of climate change is also impacting Australia’s snow season.

Since 1954, the peak snow depth at Spencers Creek has dropped by around 0.5 cm per year, or 5 cm per decade. However, there is a large amount of variability from year to year. The average dates of the season’s peak snow depth and last snowmelt have also moved slightly earlier in the season.

What can we expect this season?

This year’s Australian snow season is likely to be influenced by El Niño, possibly a very strong or ‘super’ El Niño. As of mid-May, this is currently unlikely to coincide with a positive IOD, although some forecast models do hint at the possibility of a positive IOD during winter or spring.

The presence of El Niño and the background influence of climate change increase the likelihood that the Australian Alps will see a below average peak snow depth this season. However, it will only take a few decent snowfalls to offset the influence of El Niño, so even with an elevated chance of below average snow this season, it’s not guaranteed.

In the near-term, weather models are not currently showing signs of any major snowfalls in the final two weeks of May. This means that winter, which begins on June 1, will most likely start without much natural snow on the ground in the Alps.