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Long-range forecaster offers sneak peek into upcoming snow season

Ben Deacon and Kate Doyle, Saturday May 12, 2018 - 15:51 EST
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Ella Hocking made the most of the season's first snow. Now it looks like there's more on the way. - ABC

There is something miraculous about the sight of snow falling in one the hottest, flattest and driest continents on Earth.

Heavy blizzards like the one that has just hit the Australian Alps are rare, and despite huge advances in forecasting, making long-term predictions about Australia's ski season is notoriously difficult.

"The bureau doesn't issue an official snow season outlook," said Andrew Watkins, the Bureau of Meteorology's head of long range forecasts and an avid skier.

"The problem with snow is a big dump at the right time may make it a fantastic season. It might be a completely random weather event, rather than driven by climate."

Dr Watkins cautioned against reading too much into this week's snowfalls.

"We've had early snowfalls in some great years and we've had some early snowfalls in some stinker years," he said.

Big dumps of snow in May can be the start of huge ski seasons, as was the case in 1960 and 2000, or they can be the early start of a poor season, as happened in 2006 and 1965.

On the other hand, two of the biggest years on record — 1956 and 1981 — had almost no snow in early June.

"That said, we're not in a bad space for the ski season coming up," Dr Watkins said.

The El Nino Southern Oscillation, or ENSO, is in a neutral phase this year.

That means it is neither El Nino nor La Nina, which is good news for skiers. Historically, years that are neither El Nino nor La Nina have more consistent snow.

El Nino years are drier and hotter, and El Nino seasons have 30cm less snow on average, and close two weeks earlier.

"Interestingly, La Nina years tend not to be the best either," Dr Watkins said.

"If you have a strong La Nina year, you might have plenty of precipitation, but sometimes it comes down as warm rain during the season rather than necessarily snow.

"It can have more clouds that can act like a blanket at times, trapping in more heat. So the risk of warm rain is a bit higher in La Nina events."

There is another lesser-known climate driver called SAM, or the Southern Annular Mode, which has a big influence on winter rain and snow.

"If you have a positive Southern Annular Mode or positive SAM event, our westerly winds can be too far south and tend to reduce the snowfall," Dr Watkins said.

"But if you have a negative SAM, things are a little further north and that brings up a bit more of that moisture from the southern ocean and that tends towards better snow periods."

Snow depths in negative SAM years average nearly two and a half metres at Spencers Creek in the Snowy Mountains, almost 80cm more than positive years.

SAM has been positive for much of the year, influencing the dry weather the south has experienced.

Right now, SAM is not locked into a positive or negative pattern.

The problem with SAM is that it can only be predicted a few weeks ahead, limiting its value for long-term forecasts.

The other big factor influencing snow seasons is of course climate change. Average snow depths have declined over the past 25 years, although there have been numerous above-average seasons in that time.

Each season, Australian ski fields hope for the best but they are also planning for the worst by investing heavily in snowmaking.

"Since mid-April, we've been using SnowFactory's refrigeration technology to make a stockpile of snow," said Buller Ski Lifts general manager Laurie Blampied.

"We've now got nearly two full Olympic swimming pools' worth."

Snow that makes it to mid-June will generally stick around into August. But after then, Dr Watkins said, climate change was causing seasons to finish earlier.

"We're tending to see those warmer conditions in September now. And again, if they match up with rainfall events, it tends to give these warm rain events that kill off the season."

As for reports that Australia is in for its coldest winter on record, the Bureau of Meteorology does not predict this happening.

"We're coming off the back of Australia's warmest January to April on record," Dr Watkins said.

"We also haven't had a coldest month on record or a coldest season on record for Australia as a whole since October 1975. So the chance of having a coldest winter on record is pretty low."


© ABC 2018

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