Where the snow comes from, and the decade it didn't

The Pacific track

The westerlies drive everything. Between roughly 35° and 55° South, the Southern Hemisphere's prevailing winds carry moisture-laden air eastward off the Pacific, and when that air meets the Andes it rises, cools and releases precipitation on the Chilean slope. What crosses the range into Argentina arrives much drier — the mountains wring the system out — but in a good year the spillover is enough to build a deep, lasting snowpack on the eastern flanks from Mendoza south to Tierra del Fuego.

What distinguishes the Patagonian and Andean snowpack from, say, the Alps or the Rockies is the scarcity of events. The Atlantic delivers almost nothing this far inland. A typical season at a resort in the central Andes might receive its entire annual accumulation across eight to twelve significant storm cycles. That is not a slow month in Colorado; that is the whole season's ledger. When two or three of those systems weaken before they arrive, or track too far north or south, the resort does not have a rough patch — it has a lean year. When that pattern repeats for a decade, the deficit becomes a documented climatic signal.

The zonda — a warm, dry föhn wind that descends the eastern face of the Andes — makes the arithmetic crueler still. A single sustained zonda event can strip weeks of accumulated snow from an exposed slope in under forty-eight hours, returning moisture to the atmosphere rather than the snowpack. The Cuyo region around Mendoza is most exposed; Cerro Catedral and the wetter southern latitudes suffer less, but no resort is immune. A hard zonda following a mediocre storm cycle is a compounding loss.

What the 2010s actually recorded

The central and northern Andes entered a prolonged dry period around 2010, a drought — sometimes labelled the "Megadrought" in Chile — that ran, with interruptions, through the following decade and into the early 2020s. Its Chilean character was the more dramatic: river flows, reservoir levels and the Santiago water supply all felt it. On the Argentine eastern slope, the signal was present but different in texture. Research published by the Center for Climate and Resilience Research documented the drying trend using instrumental records and tree-ring proxies across the central Andes, confirming that the period from roughly 2010 to 2020 was anomalous within at least the last century.

For the resorts, the dry years were not uniformly snowless. Las Leñas, sitting above 2,200 metres in the Mendoza province mountains, still opened and still ran the Marte chair in some of those seasons. What changed was the base: shallower, arriving later, gone sooner, and vulnerable in ways that a strong accumulation season would not be. The intermediate terrain stayed skiable; the high faces above Marte, which in a fat year can hold a metre-deep slab of dense Andean névé through October, became lottery tickets.

Further south the signal was less acute. Cerro Castor near Ushuaia and other resorts of the far south operate at latitudes where the storm track is more reliable and the temperature margin more forgiving. Their snowpack thinned during the bad years but not in the same proportion. The geography of drought in the Andes is itself a function of latitude: the megadrought was primarily a central-Chile and central-Argentina event, broadly between 30° and 40° South, and it weakened northward and southward of that band.

At Chapelco above San Martín de los Andes and at Cerro Catedral outside Bariloche, the dry period was measurable and occasionally brutal in individual seasons — 2012 and 2016 are cited in operational memory as particularly thin — without reducing either resort to closure. The southern position of the Bariloche cluster, and the way Cerro Catedral's broad terrain can still produce skiable conditions on a compressed snowpack, gave them a buffer the northern resorts lacked.

How a shortfall is counted

Argentina's snowpack is measured by the Instituto Nacional del Agua, using a combination of manual snow courses — timed visits to fixed transects where an observer pushes a tube into the snowpack and weighs the extracted core — and electronic snow pillows, which report continuously via telemetry. The INA publishes annual water-equivalent data for major Andean basins, and it is this record, rather than any ski resort's opening-day announcement, that makes a dry decade legible as a hydrological fact. The INA's public basin hydrology data allows the decade's shortfall to be read directly, basin by basin, in millimetres of water equivalent rather than impressions of powder days.

The distinction matters. A snow course measures how much water is locked in the pack at a given moment; it says nothing about how the skiing felt. A resort might contrive a respectable ski season — grooming compressed snow, opening terrain selectively — while the basin-wide water-equivalent figure remains 30 percent below its long-run mean. The two numbers answer different questions, but the hydrological record is the one that persists after the lifts close. When agronomists in Mendoza's wine country and city engineers in Neuquén talk about the decade, they are reading the same INA columns as the glaciologist; the ski resort is only one downstream consequence of a diminished pack.

The snow pillow is a pressure transducer buried under a flexible metal plate; as snow accumulates, the weight registers as a continuous water-equivalent signal. The pillow's deployment and physics are described by the World Meteorological Organization in standard hydrological guidance. For a country whose Andean catchments supply drinking water, irrigation and hydropower across the eastern drylands, the pillow network is infrastructure, not a winter sport curiosity.

What the decade taught

The 2010s confirmed what the storm arithmetic already implied: the Andean snowpack has almost no redundancy. In a mountain range where eight or ten Pacific systems constitute a full season, a modest shift in storm track frequency compounds quickly into a hydrological event. The resorts that weathered it best were those farthest from the drought's centre of gravity — southerly, at latitudes where the westerlies track more reliably — or those sitting high enough that even a reduced snowfall arrived as snow rather than rain.

The decade also demonstrated that the snowpack's failure is not primarily a ski-resort story. The river that flows east from Las Leñas toward the Atuel irrigates farmland for hundreds of kilometres. The snowpack is a reservoir without walls, filled each June and drawn down each spring, and a decade of underfilling has consequences that outlast any single winter. The resorts are the most visible part of that system, but they are not the most consequential one.