There is a way of knowing something important is happening in Mendoza without understanding a word of what is being said around you: in the afternoon, all of a sudden, everything starts closing. Street tables are taken in, people go inside, and the sky takes on an odd colour, somewhere between yellow and brown.
It is not a storm. It is the opposite of a storm: a wind that arrives without a drop of water and raises the temperature instead of lowering it. It is called the zonda, and in this part of Argentina it is not one more weather event: it is an occasion with a name of its own.
01 The day the air changes
The first thing to understand is that the zonda is not just any strong wind. Its defining feature is not speed but the combination of two things: extreme dryness and high temperature, in the same push of air.
During zonda warnings, winds of between 30 and 45 kilometres an hour are recorded, with gusts that can exceed 60, and to that is added reduced visibility from the dust it lifts. At altitude, speeds can exceed 240 kilometres an hour.
But the wind figures tell only part of it. What makes the zonda a different matter is that relative humidity collapses and temperature rises at the same time, so that in the space of an hour the air goes from normal to something that dries out anything exposed to it.
02 What the zonda actually is
Technically it is a foehn wind, the same mechanism that produces the foehn of the Alps or the chinook of the Rockies. It appears on the eastern side of the Andes and, to exist at all, it needs a very high mountain barrier. Here it has one.
The process has three steps. Moist air from the Pacific is forced to rise up the Chilean face of the Andes, to altitudes of the order of 6,000 metres. As it rises it cools, and as it cools it drops its humidity as precipitation on that side.
It then comes down the Argentine side, by now without water, and as it descends it compresses and warms. What reaches the Mendoza plain is, literally, the same air as before minus its humidity and plus its heat. Hence the very characteristic feel of it.
03 When it blows and how long it lasts
Here is the practical fact worth noting down: in 90% of cases, the phenomenon occurs between May and November. Which is to say, it is not a summer wind; it is a winter and spring one.
It also has a timetable. Most often it begins in the afternoon, between noon and six, and lasts between one and twelve hours. In long episodes it can come back intermittently for two or three days running.
That calendar has a direct consequence for travellers. The months when the plain is quietest for rain — July leaves 5 millimetres, June 5.7 — are exactly the heart of the zonda season. Clear skies do not mean a guaranteed day here.
04 Why the body notices
What sets the zonda apart from other strong winds is that local people do not talk about it the way you talk about the weather, but the way you talk about a physical complaint. And there is reason for that: the symptoms are documented and fairly consistent.
The commonest are headache, dry skin and mucous membranes, eye and throat irritation, difficulty breathing and fatigue. In sensitive people it can also set off respiratory allergies, asthma attacks and sleep disturbance.
And there is a measurement that goes beyond sensation. A multicentre study verified that days of strong zonda increase emergency visits and admissions for hypertension and cardiovascular complications, with average coronary unit admissions in Mendoza rising markedly compared with normal days.
05 The paradox: the same wind brings the water
Here is the part that changes how you look at it. The zonda is, down below, a dry wind that parches everything it touches. But up above, in the high mountains, the same weather situation goes with significant snowfall.
Contrary to what would seem logical, in this arid region that snow input turns out to be key for glacial accumulation, rather than a wind that strips snow away. The same episode that parches throats in the city is loading the mountain with solid water.
And that snow is, literally, the water the oasis is irrigated with. So the most uncomfortable wind in the Mendoza calendar is part of the same mechanism that allows the province's green 4% to exist. It is not an enemy of the system: it is one of its pieces.
06 What to do if it catches you
First, do not read it as bad luck with the weather and carry on with the plan. A zonda day is not a windy day: it is a day when it makes sense to reorganise and leave anything requiring hours outdoors for another time.
The usual recommendations are simple and they work: drink water steadily, avoid prolonged exposure, protect eyes and airways, and keep indoor spaces well ventilated. None of that is excessive in air that can be left with almost no humidity at all.
And second, something that helps you read the place. If on a zonda day you notice the conversation change, people being shorter with each other, or someone cancelling without much explanation, do not take it personally or as local strangeness. It is a wind with a name of its own and a clinical record, and the whole city treats it accordingly.
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