How to Know When it's Going to Snow

Snow forecasting for the Southern Alps is mixture of art and science, because there are so many variables at play. New Zealand sits smack dab in the middle of one of the most active weather zones on the planet. We're subject to influences from the tropical South Pacific, the mighty Southern Ocean, and Australia. El Nino and La Nina also play a significant part in snowfall throughout the season. All that means weather forecasting for New Zealand is extremely difficult and the forecast can change very rapidly.

So lets go through each of the weather patterns one by one and see what they contribute to our snowfall.

The Southern Ocean is an uninterrupted band of cold water that rings the globe in the latitudes between 60 degrees South of latitude and the coastline of Antartica. The water is always very cold and the wind blows hard from the west - it's not called the 'Screaming 60s' for nothing. 

Now a second factor comes into play - the Southern Annular Mode (SAM). This is a rollercoaster shaped pattern of air movement that has three different phases Positive, Negative, and Neutral. If you love snow like we do at Outside Sports then you're hoping for a Negative SAM, which is what we have in 2026. A Negative SAM brings its roller coaster waves up onto New Zealand from deep in the Southern Ocean bringing with it cold air and intermittent pulse of moisture laden air, which when they combine and bump into New Zealand falls as snow. The colder the air, the less moisture it can hold and hence the lighter and fluffier the snow that comes down. 

This year courtesy of the SAM we've been fortunate to have a snowy pulse of cold, moist air every week. This map shows the SAM roller coaster in action.

Sometimes when we've all done our snow dances, and the stars align we get a low pressure system off the South East Coast of the South Island. When this is fed by cold moist air from the SAM it literally fires snow at the South Island, and all our ski fields get the benefit. If we had a pick a direction for our snow, it would definitely be from the South East, because it's time to get out our powder skis!

The map above shows a Warm Advection event impacting the Southern Alps. The words warm and snow don't really seem to go together, but when it comes to snow for the Southern Lakes ski fields this odd combination seems to work magic - especially for Treble Cone which has a mainly northerly aspect. Warm Advection happens when a warm Northwesterly airstream rips down the Tasman sea from the tropical North Eastern tip of Australia. On the way it picks up a lot of moisture and is often termed 'an atmospheric river.' On its own this has system has the potential to wash a lot of snow away. And exactly that happens sometimes.

BUT! If the SAM is doing its thing properly, cold air is blasting up from the freezing cold Southern Ocean at the same time. Because cold air is more dense, when the two air masses meet the cold air drives in underneath and the moisture that the warm air drops gets chilled on the way down and falls as snow. Warm Advection events can differ in the quality of the snow they make. It can be wet 'hot pow' or if the cold air really gets in there, it can be light and dry. Often the quality of Warm Advection snow depends on where you are, and it's generally better the further South you go.

Warm Advection tends to dump a lot of snow very quickly. 6-8cm per hour, and up to 1 metre of snow during the course of the weather event is not out of the question especially for TC and Mt Hutt.

2026 is a strong El Nino year and that combined with the Negative Phase of the SAM means we're getting regular doses of snow. Even low elevation ski fields like Coronet Peak are enjoying excellent conditions, and the season will be a long one.

With El Nino comes a predominant South Westerly air flow for New Zealand, which means cold moist air and great snow conditions. On the other hand, La Nina works in the opposite direction. La Nina pushes down warm tropical air from the South Pacific, which is not what you want for snow. However in most La Nina years we still get a few solid snow bearing systems from the Southern Ocean, but they're less frequent and less snowy, especially at low elevation ski fields like the Canterbury clubbies.

Australian weather systems are heavily influenced by the Indian Ocean Dipole (IOD) which refers to see sawing temperature in the Indian Ocean. Currently the IOD is in a Positive Phase which tends to make Australia drier. When that's combined with a strong El Nino, as we have now, that also means that the snowy weather systems generated in the Southern Ocean tend to skip Australia and make landfall in New Zealand. This map shows the IOD doing it's thing in late August 2026.

If you're keen skier or snowboarder in New Zealand you are probably also an avid weather junky. While you can get reasonably accurate snow reports from sources like Snow Forecast, nothing beats being able to look at weather models and make your own predictions.

Predict Wind and Windy are the most popular weather sites for sports people whose sports are weather dependent. They have a choice of different weather models to choose from - and ECMWF seems to be the most consistently accurate for New Zealand - up to about seven days ahead of time. NZ Metservice is also good, but is best used for forecasts up to three days out. They also tend to be a bit hysterical with their wind, rain, and snow warnings, probably because it's a government department. Overall it's best to look at multiple different forecast models and then take an average.

So there you have it, a basic run down on snow producing weather systems and what to look for the next time you're in front of a weather map.