The year in the Mendoza oasis
The figures are for the city of Mendoza, at 746 metres and in the middle of the northern oasis. The annual total is 223.2 millimetres and 2,975.8 hours of sunshine: a very sunny cold desert where what changes from month to month is not how much rain falls but when.
Almost every famous wine region in the world shares one pattern: wet winters, dry summers. It is the Mediterranean scheme, and it is what lets the grapes ripen with no water on them just before picking.
Mendoza does exactly the opposite. Here winter is the dry season and summer the wet one, in a place that barely gets 223 millimetres a year. That detail changes the trip calendar, the harvest risk and even the look of the landscape.
01 A desert that rains the wrong way round
Lined up, the city's millimetres draw the curve without ambiguity: 47.2 in January, 40.8, 31.6, 18.5, 11, 5.7, 5, 7.9, 12.3, 11.2, 22.1 and 24.7 in December. The maximum is in high southern summer and the minimum in deep winter.
Between November and March, 166.4 millimetres of the annual 223.2 pile up: almost three quarters in five months. The four months from May to August add up to 29.6 millimetres between them, less than January alone.
And even so it is not a cloudy place. January records 316.2 hours of sunshine and December 328.6, the year's maximum. That a month can be the wettest and among the sunniest has only one explanation: the rain does not last, it arrives in short afternoon storms.
02 Where the water that gets used falls
Here it helps to separate two things that constantly get confused. One is the rain falling on the oasis, those 223 millimetres, which is nowhere near enough for anything. The other is the water used for irrigation, which does not come from the sky over the plain.
On the high Andean slopes annual precipitation passes 600 millimetres, and there it is almost exclusively winter precipitation and almost always snow. That snow melts in spring and summer and comes down the rivers to the oases.
So the water calendar has two storeys out of phase. Above, it snows in July; below, irrigation happens in January. A traveller looking only at the lowland table cannot see where the green comes from, and one looking only at the mountain cannot see why the plain is dry.
03 Why summer is the problem
That the year's little rain should fall in summer is not neutral for farming: it is the worst possible timing. November, December, January and February are the months when the grapes set, swell and ripen, and they are precisely the storm months.
The specific risk is not the water, it is hail. In this region's viticulture hail is a frequent and serious problem, and it is tied exactly to that kind of convective afternoon storm that arrives with the heat.
For a traveller this shows up in two visible ways. One, the nets covering many plots, which are not shade cloth but protection. The other, that January and February afternoons can turn in half an hour, even in a month with more than three hundred hours of sunshine.
04 March, the month the province works
If one month sums up Mendoza, it is March. Rain has come down to 31.6 millimetres over 4.8 days, highs to 28.1 degrees and lows sit at 15.7. It is the first month of the year when the heat eases before the cold has arrived.
And it is the central month of the harvest. That means the whole oasis is in motion: busy tracks, wineries working, plots picked and left bare within days. It is not a landscape at rest, it is a landscape in full work.
April continues it with less noise and better numbers: 18.5 millimetres over 3.6 days, highs of 23.3 degrees and the vine leaves turning colour. For anyone preferring the place quiet with the same weather, April is the answer.
05 The dry winter and the second country up above
The lowland winter is harsh in a way that surprises. July leaves 5 millimetres of rain, highs of 15.3 degrees and average lows of 2. June stops at 183 hours of sunshine, the year's minimum. It is a dry winter, cold at night and with nothing green.
Up above, though, it is high season for something else. The same months when the oasis is idle are the snow months in the cordillera, with the ski areas running and the high mountain closed to climbing but open to winter.
And there is a third element belonging to winter and spring: the zonda wind, which in 90% of cases blows between May and November. It is not a minor detail of the climate, it is a weather condition that changes the whole day when it turns up.
The year's four stretches
Rain falls from 31.6 to 18.5 millimetres and highs from 28.1 to 23.3 degrees. It is the central harvest month and the one after, with the oasis at work and the air already dry. The year's best combination of weather and activity.
11.2 and 22.1 millimetres of rain, with 275.9 and 309 hours of sunshine and highs of 25.7 and 29.2 degrees. The vines are budding and in November the Aconcagua park season opens. Dry, sunny and without January's heat.
The sunniest months of the year — 328.6 hours in December — and also the wettest: 24.7, 47.2 and 40.8 millimetres. Highs of 32.8 degrees in January and afternoon storms with hail risk. Very bright and fairly uncomfortable.
Between 5 and 12.3 millimetres a month and the year's sunshine minimum in June, 183 hours. Average lows drop to 2 degrees in July and the oasis landscape is bare. It is, on the other hand, snow season in the cordillera and zonda season on the plain.
06 How to choose the month
If the trip is about the oasis and what happens in it, the answer is March, with April as second choice. You see the harvest, rain has already come down to 31.6 millimetres and highs are 28.1 degrees instead of 32.8.
If the trip is about the mountains, the answer is November or December, when the Aconcagua provincial park season opens and the high passes are usable. November combines 309 hours of sunshine with only 22.1 millimetres of rain.
And if it has to come down to one month that works for almost everything, it is October: 11.2 millimetres over three wet days, 275.9 hours of sunshine and average highs of 25.7 degrees. There is no harvest and the high mountain has not opened yet, but it is the month with the fewest objections in the calendar.
