The year in Salta, month by month
The month-by-month figures come from Salta airport, 1991–2020 series, at 1,187 metres: 738.3 millimetres a year over 88.6 days. They are contrasted with San Antonio de los Cobres, at 3,775 metres and 103.9 millimetres a year, which marks what happens on the puna.
Anyone travelling from the northern hemisphere arrives with a learned reflex: summer is the good season and winter the bad one. In Salta that reflex leads to booking precisely the worst month of the year.
And not because it is cold, but because here summer is when it rains.
01 The calendar is upside down
The province runs on a summer rainfall regime, which is the normal pattern at this latitude and in this position relative to the mountains. Damp air arrives from the east in the warm months and unloads; in the cold months, it simply does not arrive.
The result is a calendar split into two very unequal halves. There is no long transition: there is one month of descent, April, and one of ascent, November, and between them two blocks that behave completely differently.
It is worth being clear about it because it affects more than umbrellas: in the wet half, the gravel roads of the valleys and the puna stop being reliable, and some stretches close because of floods.
Twenty-two point nine millimetres in five months: three per cent of the year's rain falls across the whole cold half.
02 Twenty-three millimetres in five months
The figures from Salta airport, 1991–2020 series, leave no room for interpretation. May: 9.7 millimetres over 3.8 days. June: 2.5 over 1.7. July: 2.7 over 1.7. August: 2.3 over 1.5. September: 5.7 over 2.1.
The five-month total is 22.9 millimetres over 10.8 rainy days. Against an annual total of 738.3 millimetres over 88.6 days, that is 3.1 per cent of the water and 12.2 per cent of the days.
And the temperature of those months is not hostile. Average highs run from 19.8 to 24.7 degrees, that is, short-sleeve days in the sun. August, the driest month, has an average high of 22.7.
03 And eighty per cent of the water in four
At the other end, December gives 138.4 millimetres over 13.0 days, January 197.1 over 15.4, February 147.3 over 14.4 and March 107.3 over 13.7. The four add up to 590.1 millimetres, 79.9 per cent of the annual total.
In January it rains one day in two. And it is not drizzle: it is 197 millimetres, more than Madrid collects in an entire year, concentrated in afternoon storms.
Humidity follows suit. In March it reaches 82.9 per cent, its annual maximum, against August's 60.4. With highs of 25 degrees, that twenty-two-point difference is more noticeable than the degrees.
04 Winter's price: the nights
The dry season has a cost and it is at dawn. In July, the average minimum in the city of Salta is 2.9 degrees, and the station's absolute record is −8.7, recorded in August.
The difference between day and night is what surprises: in July, an average maximum of 19.9 degrees and a minimum of 2.9. Seventeen degrees of range within the same day, a direct consequence of dry air and clear skies.
In summer the opposite happens. In January the maximum is 27.7 and the minimum 16.8: eleven degrees of range. Humidity and cloud hold the heat and the night does not cool.
05 And altitude, which multiplies everything
All of the above applies to the city of Salta, at 1,187 metres. If the trip climbs to the puna, you have to recalculate, because the same calendar becomes far harsher.
In San Antonio de los Cobres, at 3,775 metres, July's average maximum is 11.9 degrees and its minimum −7.7. In January, 20.4 and 4.2. That is, a winter night on the altiplano is eight degrees below zero while in the city it is three above.
The rainfall regime, by contrast, is the same and even more marked: 44.0 millimetres in January and 0.0 in July, out of an annual total of 103.9. On the puna, the dry season is literally dry.
06 How to choose the month
May to September, without hesitation, if the plan includes the valleys, the puna or any road that is not tarmac. Those are five months with 22.9 millimetres in total and highs of 19.8 to 24.7 degrees.
Within that window, September is the most comfortable month: still dry, with 5.7 millimetres, and lows have risen to 7.7 degrees. July and August are the driest but also the coldest at dawn.
And if you want to see the north green, April is the answer. Rain has dropped from 107.3 to 42.1 millimetres, the sky is already opening and the landscape still keeps its summer colour. It is the only month that combines both, and it does not last.
The year's four stretches
From 2.3 to 9.7 millimetres a month over 1.5 to 3.8 days, with highs of 19.8 to 24.7 degrees. Five straight months with no meaningful rain: the only window in which the whole province is workable at once.
From 23.9 to 59.3 millimetres over 5.3 to 9.0 days, with highs of 26.9 and 27.6 degrees and the absolute heat record in November, 39.9. It still works, but the afternoon is no longer reliable.
590.1 millimetres over 56.5 days: 80 per cent of the year's rain in four months. Humidity between 77 and 83 per cent and unreliable gravel roads in the valleys.
42.1 millimetres over 7.0 days, highs of 22.9 degrees and lows of 12.2. The rain has gone and the countryside keeps its summer green: the only month when both things coincide.
