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One of the more interesting developments has been the atmosphere outperforming the guidance. Snow has developed earlier and at lower elevations than forecast, despite the leading models maintaining freezing levels well above the alpine peaks through Wednesday night. Observations instead showed temperatures and snow levels running considerably colder across the Australian Alps, highlighting just how difficult these transitional events can be to model. The broader forecast remains on track, with the cold front expected to deepen through today before the heaviest snowfall arrives from around midnight into Friday morning. Gusty west to northwesterly winds will accompany the system before easing on Friday, followed by a return to favourable snowmaking conditions during nighttime hours, into next week.

Make hay while the sun is shining as this is likely to be the strongest polar push until the next substantial fall circa 17/18th July with potentially a short sharp dusting or so around the 12/13th.

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TL;DR

• Strongest daily winter AAO/SAM signal since June 2016 (Strong El Nino)

• Walker-circulation and ENSO moblise the MJO

  • A long wave trough is expected through south-east Aus, July 2-6

    • Significant pre-frontal rain is expected in the Aus alpine, July 1-2

    • 10-15cm snow, expected across ski areas July 3-5

• NZ snow returns July 4-6

• South American Ski Areas low tide and in a holding pattern

• Polar vortex is in high variability

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Southeast Australia will benefit from the strong likelihood of light to moderate snowfall during the aforementioned July 2nd–6th window.

Thanks to the Madden-Julian Oscillation (MJO) and the Walker Circulation, the equatorial Western Pacific is forecast to enter a highly active convective phase over the next fortnight. For Australia, this setup strongly favours a longwave trough pattern that opens the door to—well—finally some snow. While early June's snowfalls across the southeast were also driven by the Madden-Julian Oscillation (MJO), this upcoming phase is shaping up to be a stronger, more sustained pulse. Crucially, however, a stronger pulse does not automatically translate to greater snow totals.

Sadly, a strong +SAM phase is keeping the polar air on tight leash, leaving high-pressure ridging firmly in control. On June 21st, the daily winter SAM peaked at +3.85—the highest winter reading in a decade, falling just shy of the +4.05 registered on June 14th, 2016.

NB. The highest recorded SAM value (of all seasons) was achieved the following Spring in Sep, 2016 where it registered +4.64.

As with the early June event, the Rossby wave is forecast to peak west of the Alps. This means the system is expected to sweep across southeast Australia on its downstroke, rather than delivering an immediate polar outbreak from the south.

Meteorologically, this configuration promotes anticyclonic wave breaking, establishing a warm conveyor belt that funnels a tongue of subtropical moisture into the Alps ahead of the front. Because the Australian Alps currently have only a negligible snowpack, the rainfall is less problematic than it would be later in the season. Even so, a prolonged period of heavy rainfall is likely on June 30 and July 1 before colder polar air arrives behind the main feature, allowing precipitation to transition to snow.

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60-80mm of rainfall is likely in this timeframe.

Model divergence increases markedly from Thursday onwards, which is entirely expected given the seven-day lead time. Encouragingly, however, the AI guidance remains in remarkably close agreement, consistently pointing towards 10–15 cm of snowfall across the ski areas between Thursday evening (2 July) and Sunday (5 July).

Snow is expected to reach lower-reaches of all major ski areas with snow falling as low as 1300m ASL, briefly on Friday (3rd).

While this forecast may evolve if the models are overestating the strength of the MJO, confidence remains relatively high. That confidence stems not only from the consensus among the AI guidance, but also from unanimous support for a strong high pressure system building in behind the trough (5th), reinforcing a warmer and more settled pattern into early July.

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Australia’s Loss Is NZ’s Gain

As confidence grows in a strengthening ridge building behind southeast Australia’s early July trough, attention shifts across the Tasman. Should this pattern evolve as currently forecast, it would establish a favourable south-westerly flow across New Zealand’s South Island between 4–6 July, potentially delivering the country’s first major snowfall event of the season. Current guidance supports widespread accumulations of 15-30cm across the major ski areas, although confidence remains reliant on the persistence of the current model agreement over the coming week.

While all South Island ski areas stand to benefit, the Canterbury fields may emerge as the biggest winners. Several model solutions introduce a south-easterly feed during 6th July, enhancing snowfall along the eastern side of the Main Divide and increasing the potential for locally higher snowfall totals across the region.

South American Dreaming

The outlook across the Chilean and Argentine Andes remains at odds with the widespread pre-season expectation that a strong El Niño would deliver an active start to winter. Instead, the pattern continues to favour extended periods of settled weather, with little indication of meaningful snowfall across the major ski regions in the immediate outlook.

For resorts such as Valle Nevado and Nevados de Chillán, current long-range guidance continues to favour predominantly clear conditions through the first week of July. There are, however, early signs that the pattern may become more favourable for snow around 8–10 July, with ultra-long range guidance tentatively signalling a return to snowfall. Given the lead time, confidence in this signal remains low, but it represents the first indication of a potential pattern change after an unexpectedly quiet start to the season.

The Wildcard: Southern Polar Vortex

The Southern Hemisphere polar vortex is currently showing an unusual vertical structure, with very strong winds in the lower stratosphere and more typical conditions higher up. This follows a volatile June, which included an early warming event and a rapid strengthening of the circulation later in the month.

What this leaves us with is not a simply strong or weak vortex, but a layered system where different parts are behaving differently. That matters because it can change how the vortex responds to incoming atmospheric disturbances.

The next key influence is the Madden–Julian Oscillation moving through the Western Pacific over the next couple of weeks. As it strengthens, it is likely to increase wave activity moving into higher latitudes. The question is how that energy interacts with an already tightly wound lower stratosphere.

A strong vortex like this is generally harder to shift. But when the structure is uneven like it is now, the response becomes less predictable. For now, the most likely outcome is not a sudden breakdown, but a period of increased variability in the second half of July, depending on how this wave activity plays out.

The polar stratosphere will be an important feature to monitor through the coming weeks, particularly as a potential indicator of any mid-season shift in Southern Hemisphere winter patterns should this evolving wave activity begin to take hold.

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TL;DR

• Light alpine snow for south-east Australia, this weekend.

• Long Range: +SAM continues to favour ridging over SE Australia.

• El Niño has officially been declared by the Bureau of Meteorology.

• MJO is likely to return to the western Pacific in late-June.

• Early July is emerging as the next window worth monitoring for renewed snow opportunities.

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If you’ve followed The Snowstack for any length of time, you’ve probably noticed a recurring theme whenever a new system appears on the horizon.

The conversation often centres on freezing levels, instability, dynamic cooling and whether the atmosphere can somehow squeeze out a little extra cold. Rather than discussing snowfall totals, we often find ourselves debating whether it will be snow, porridge or rain.

Next week’s system in south-east Australia is no exception.

At first glance, that may seem strange. After all, isn’t winter weather simply about whether cold air arrives with the storm?

Increasingly, the answer is no.

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Australia’s alpine climate has always danced with the devil close to the ‘wintry mix’ boundary. But as our climate trends warmer, more systems now thread the needle, edging closer to that threshold. As a result, the atmosphere often needs a helping hand to turn a marginal setup into a productive snow event.

This is where some of the terms you regularly see in forecast discussions become important.

The first is evaporative cooling.

In simple terms, rain or snow falling through dry air cools the atmosphere. Many air conditioning units work on a similar principle. As precipitation (snow) falls, it partially evaporates or melts, removing heat from the surrounding air and causing temperatures to drop. This process can significantly lower snow levels, which is why forecasters pay close attention to humidity as a storm arrives.

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We are seeing that play out aga…

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Model guidance has struggled in recent days, with competing weather models at times losing coherence on the event. However, recent runs have shown growing confidence in the well-timed system.

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The Australian and New Zealand (ANZ) snow season is a notoriously fickle beast, threading the needle between maritime moisture delivery and marginal alpine temperatures. While climate drivers such as El Niño and the Southern Annular Mode help shape the broader seasonal outlook, winters are often defined by just a handful of major snow events. It can take only one or two well-timed systems to completely transform the snowpack.

Climate drivers represent the broader background state of the atmosphere: the large-scale circulation patterns influencing our region, often driven by processes occurring far beyond Australia and New Zealand. Understanding this background state helps contextualise the likely behaviour of the season at longer timescales.

Located within the mid-latitudes, the ANZ region is influenced by both tropical and polar climate drivers. The primary tropical drivers include the El Niño–Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Madden–Julian Oscillation (MJO), while the polar influences include the stratospheric polar vortex (SPV) and the Southern Annular Mode (SAM/AAO).

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NB. The Southern Hemisphere seasonal outlook for the forthcoming winter will be released to paid subscribers on Monday, 11 May. Support this independant snow outlook resource by subbing today:

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There is an autumnal chill settling over Australian and New Zealand resorts, and early signs are materialising. A 20–30 cm snowfall in New Zealand was enough to see Hanmer Springs spin its surface lift late last week, marking the first operational movement of the season:

Focus now shifts to a potentially cold system for south-east Australia. Current guidance suggests a midweek arrival, accompanied by one of the coldest early-season air masses since May 2019, when parts of Victoria experienced snowfall down to 700 m.

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Since then, the outlook has progressed considerably. It’s a clean signal on paper, but not ideally placed for the Aussie Alps. As the system shifts east, the …

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While stratospheric sudden wa…

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Back in early February, we flagged that the stratosphere was undergoing a series of warming events. Those perturbations have continued through the month, weakening the stratospheric polar vortex and setting the stage for a more significant disruption.

The observational signal became clear by mid-February and is now propagating downward into the lower stratosphere. A major warming event is expected in early March, likely resulting in a wind reversal at the 5–10 mb level. In practical terms, this marks a substantial disruption to the high latitude circulation aloft.

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This is not an unusual event in a climatological sense, but it often reshapes the hemispheric pattern through March. In essence, this is gearing down of winter in the northern hemisphere and often results in warm/cold pool tussles.

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Stratospheric Polar Vortex Outlook Summary

The stratospheric polar vortex is a broad ring of strong westerly winds that encircles the Arctic high above the surface, strongest through winter as the pole cools and darkness sets in. When consolidated, it locks the coldest air into the high latitudes and supports a more zonal, progressive mid-latitude pattern. When disrupted by wave activity propagating upward from the troposphere, the vortex can weaken, become displaced or even reverse, allowing cold air to spill further south.

In this case, the initial trigger was an extreme warming event in the upper troposphere observed in late January. That tropospheric amplification has propagated upward, with the upper stratosphere responding over the past fortnight. We are now seeing a marked temperature rise through the 5 hPa layer and a reversal of zonal winds near 2 hPa (figure below), clear evidence that the vortex has been significantly weakened aloft. The disturbance is most pronounced in the upper levels for now, but the structure beneath is beginning to respond.

Way does this matter? We’re seeing a the start of the continued pertubations that will have lasting impacts on the worthern winter in around 2-3 weeks time.

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Inline with our last update, Niseko’s weekend system has delivered ~20cm since Thursday. A continuation of showers will persist through Monday where a ridge offers a clearing trend, ahead of some chiefly heavy snow showers on Wednesday morning.

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The stratospheric polar vortex has endured an unusually disruptive winter so far. An early-season warming in November was followed by repeated large-scale disturbances, preventing the vortex from re-establishing a stable, cold mid-winter state. The latest outlook suggests the most recent disruption is not resolving cleanly, with guidance increasingly aligned on a further significant stratospheric warming event over the coming fortnight.

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The polar vortex is often invoked as a shorthand explanation for winter volatility, but its role is more structural than sensational. At its core, it represents the organised circulation of cold air around the pole, acting as a stabilising influence on the hemispheric flow. When that circulation is weakened or displaced, the containment of polar air becomes less effective, increasing the likelihood of high latitude blocking and negative phases of the Arctic Oscillation.

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The one-two hit gets underway late Tuesday across southwestern BC. In contrast, it lacks a classic mid-winter cold signature; the moisture content more than compensat…

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The week ahead is defined less by any single storm and more by how the large-scale circulation is organising itself across the Northern Hemisphere. A persistently disrupted polar vortex continues to redistribute cold air, with the most coherent and impactful cold pool anchored across eastern North America 🇺🇸🇨🇦, where winter forcing remains strong and sustained. Elsewhere, the signal is more conditional. Japan 🇯🇵 remains well positioned to capitalise on periodic cold air advection for snowfall, while much of Europe 🇪🇺and western North America sit closer to the margin, where outcomes are dictated by timing, elevation and rain snow line sensitivity.

Although another stratospheric warming phase is developing, its effects have not yet filtered down, meaning near term winter outcomes depend more on day to day pattern placement than on the overall hemispheric state.

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A quick review of the Stratopsheric Polar Vortex

Typically in mid winter the stratospheric polar vortex is relatively circular and well organised. At present, that structure has become disrupted, with cold and warm air unevenly redistributed around the pole. This has contributed to another stratospheric warming event over the past week, further weakening the vortex and driving large deviations in upper level winds. While these disruptions take time to propagate downward into the troposphere, often on the order of two to three weeks, they are a reliable signal of increased late winter variability. The pronounced east west contrast across North America now reflects stratospheric disturbances that emerged in late December.

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Spenny’s (aka Gimbal God) video from Furano (Hokkaido) last week says it all really:

Japan

The good times roll on over the next fortnight, with a strong long-wave trough anchored over East Asia for at least the next 10 days. This setup sustains a north-westerly fetch, fuelling sea-effect snow aimed squarely at central and northern Honshu.

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This broadscale shift is unfolding in the wake of the November’s extraordinary SSW event, which dislodged the Polar Vortex from the Arctic pole and allowed cold air to downwell across North America and East Asia during December.

As the deeply negative AO and NAO begin to regress—patterns that have dominated and disrupted the hemispheric flow in recent weeks—the door is opening for a more amplified, cold-driven setup to emerge.

When it comes to snowfall in the Alps, the primary moisture source is the North Atlantic, while the cold air is most effectively delivered via significant northward deviations in the jet stream. In recent weeks, however, we’ve seen a seesaw of unfavourably deep negative AO/NAO phases, which has disrupted the alignment of Atlantic moisture with cold air intrusions from the north.

The Goldilocks Zone for European Alps snow systems is ideally when the NAO and AO phases are bouncing around the neutral to neutral negative phases, which is largely where it’s loosely expected to head toward over the coming week.

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