Patagonian windsthe world’s wind, now, on the map

Look at the map above and find the south of the planet: there is a whole band around Antarctica where the particles run west to east without stopping. These are the Southern Hemisphere westerlies. Sailors named them by latitude: the roaring forties, the furious fifties, the screaming sixties. El Chaltén sits at 49 degrees south, right inside the band.

That wind exists because between the South Pacific high, near 30 degrees, and the low pressure ringing Antarctica, near 60, there is a huge pressure difference. Air runs from the high to the low, the Earth’s rotation bends it eastward, and along the whole way there is almost no land to slow it: it is the only place on Earth where the wind can circle the planet over open sea.

Patagonia is practically the only thing that gets in the way. And it does so with a mountain range and an ice field of some 12,000 km² right in the wind’s face. Pacific air arrives loaded with moisture, climbs the Andes, drops rain and snow on the Chilean side and over the Ice Field, and crosses to the Argentine side dry, warmer and sped up by the descent. It is the same effect as the Alpine foehn, every day.

In El Chaltén the relief adds its own part. The Río de las Vueltas valley runs north to south and the west wind comes in sideways through every side valley: the Fitz Roy, the Torre, the Eléctrico. Where a valley narrows, the air squeezes and speeds up. That is why town can be calm while on the Laguna de los Tres moraine, at 1,170 m and facing the ice, gusts pass 80 km/h.

The year has its rhythm. In spring and summer the Pacific high strengthens and shifts south: the pressure difference over Patagonia tightens and the wind grows, right in the months with most daylight and most visitors. In autumn it eases: March and April are the calmest months to walk, with the lenga forest turning red. Winter brings still, cold days and, suddenly, a southerly gale with snow.

And the day has its rhythm too. At night the air near the ground cools and sits still; by mid-morning the sun mixes the layers and the wind from above comes down into the valley. That is why we leave early, and why the last climb to the lake is best done before noon.

Where it hits hardest

The last kilometre and a half to Laguna de los Tres, the moraine facing the glacier: 350 metres of climb without a tree. The top of Pliegue Tumbado, at 1,500 m, open to everything. The Laguna Torre moraine, where the valley opens and the wind comes down off the Grande Glacier. And on the Huemul Circuit, the pass named for it: Paso del Viento, at 1,500 m, with the whole Ice Field in front.

Where you are sheltered: the lenga forest, the whole way to Laguna Capri and to Poincenot camp; the Río Eléctrico valley to Piedra del Fraile; Mirador de las Águilas, which looks the other way.

How to walk in the wind

Poles, always: two more points of contact. Body low and leaning a little into the wind. When a gust comes, stop, set your feet and wait; then go on. On the moraine, cross the exposed stretches one at a time and do not stop on the crest. Nothing loose on the pack. Glasses, because it lifts grit. And do not fight it: the guide picks the time and the place so the wind is one more fact and not the problem.

What we check every morning: the forecast gusts at the hike’s spot (not in town), the wind at summit height, and Fitz Roy’s cloud. If it wears a hat, it is windy up there.

Flag trees: lengas and ñires growing with every branch on the east side, as if the wind had combed them. You will see them on the climb to Laguna Capri and all along the edge of the steppe. Each one is a fifty-year anemometer.

Lenticular clouds over Fitz Roy and Cerro Torre: the “hat”. Strong wind at height flows over the massif and the air rises and falls in waves; at the crest of each wave a motionless, plate-shaped cloud condenses while the wind passes through it at 100 km/h. It is the valley’s oldest sign: wind up high, and often bad weather on the way.

Lago Viedma with sea-like waves and a band of dust blowing off its southern beaches; the Río de las Vueltas combed against its own current. And on the Ice Field, the katabatic wind: cold, heavy air sliding down the glaciers and pouring out through the valleys like an invisible river. You feel it on the Laguna Torre moraine, coming off the Grande Glacier.

The town itself is built for the wind: low, well-tied tin roofs, doors that open inward, log fences. And a habit: nobody asks whether it will be windy, only how much.

Each particle follows the real wind 10 metres above the ground. The faster it runs, the harder it blows. Tap “Speed” and the map takes the scale’s colours: blue up to 20 km/h, green up to 50, yellow up to 70, orange up to 100 and red beyond. “Temperature” paints the 2 m temperature from the same model, and “Ice and snow” shows the sea ice around Antarctica and the snow on the ground, also from the model, in today’s analysis. Next to each place is its real wind in km/h, and two marks tell you where it blows most and least in what you see. Drag to move, pinch or use the buttons to zoom (the “El Chaltén” button takes you to the massif and turns on NASA’s real relief: the range and the Ice Field; “Relief” toggles it in any view), tap any place on the planet to read its wind. The bar below plays the forecast hour by hour, up to two days ahead.

The data comes from the GFS model of the US weather service (NOAA), run four times a day on a one-degree grid. It is the same model most weather apps use. For the valley we also use forecasts at each point’s real height, the ones you see above and in the mountain forecast.

What to look for: the white band circling Antarctica (the westerlies); the eddies travelling inside it from west to east, which are the storms that reach us every few days; and how the flow squeezes crossing the Andes at El Chaltén’s latitude. Watch the map a couple of days in a row and you will understand the forecast before reading it.

It is for orientation: the model sees the planet in 100 km cells and does not see the valley. On the day, the guide decides, with the forecast for each point of the trail.