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The year at 3,399 metres
All the figures are the city's. Because average highs vary by less than two degrees all year, the scoring depends on rain, sunshine and what the thermometer says at night.
One fact about this city instantly disarms the usual question about the weather. The average high in January is 20.5 degrees; in July, 20.6. Between the theoretically warmest month and the theoretically coldest there is a tenth of a degree.
At 3,399 metres and thirteen degrees south, the sun beats down the same all year. So if you ask about the temperature in a given month, the right answer is another question: by day or by night?
01 The figure that does not move
The average high swings between 20.3 degrees in February and 22.3 in November. Two degrees of range across the whole year. Compared with any mid-latitude city, where the difference between summer and winter is twenty degrees, this is a flat line.
In practice that means daytime clothing is the same in January as in August: a T-shirt, something long-sleeved and serious sun protection, because at this altitude the radiation is intense even when you do not feel hot.
02 The one that does
The average low is another story. In January and February it sits at 8 degrees. In July it falls to 1.2. That is this city's real seasonality: almost seven degrees of difference, all of it in the small hours.
And averages hide the worst of it. The recorded cold records are seven degrees below zero in May and July, six below in August and September, and four and a half below in June. Even April has a record of two below zero.
The daily range in the dry months is enormous: from an average high of 20.6 to a low of 1.2 in July is almost twenty degrees within the same day. You will be too warm at midday and cold at six in the morning, out of the same suitcase.
03 Dry and cold are the same block
Here is the inversion that throws anyone arriving from Europe or North America. In most of the world the dry, sunny season is the warm one. In these Andes it is exactly the opposite: the cloudless months are the frost months.
The explanation is simple. The wet season's clouds act like a blanket: they hold the ground's heat through the night. When the sky clears, that heat escapes upwards with nothing to stop it, and the temperature collapses.
The year's four blocks
Rain falls from 105.9 to 38.4 and then 7.1 millimetres, sunshine climbs from 170 to 239 hours and nights are still at average lows of 6.2 and 3.6 degrees. It is the only stretch when the sky is already clear and the night cold has not yet properly bitten.
Between 3.3 and 6.6 millimetres of rain a month and up to 257 hours of sunshine in July: there are no better skies all year. The price is average lows of 1.9, 1.2 and 2.8 degrees, with records of seven below zero. It is the best season for walking and the worst for sleeping badly wrapped up.
18 and 54.5 millimetres, with 195 and 198 hours of sunshine, and nights recovering to average lows of 5 and 6.8 degrees. October's rain comes late in the day and concentrated, not as a whole day of water.
Water rises from 77.3 to 153.4 millimetres and days with rain reach 19.6 in January. February drops to 121 hours of sunshine, the year's minimum. In exchange, the nights are the mildest — 8 degrees — and the landscape turns from brown to green.
04 The problem is not the street, it is the room
And now the practical consequence almost no guide mentions. In a city where the average high is twenty degrees all year, buildings are not designed to hold heat: there is no insulation, and many places to stay have no heating of any kind.
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That means that in June or July the room wakes up at street temperature, or close to it. Before booking in those months, the useful question is not whether there is a good view: it is whether there is heating, and what kind.
05 What the wet season wins
There is an honest argument for the wet months, and it is not only price. January and February have the mildest nights of the year, with average lows of 8 degrees against 1.2 in July. If the night cold is your problem, the sum reverses.
And there is the colour. The annual total is 727.7 millimetres over 106.1 days, and almost all of it falls between November and March. That water is what turns green a landscape that in August is brown and yellow.
But the cost has to be said: 19.6 days with rain in January and 121 hours of sunshine in February, the calendar's minimum. That is not an afternoon shower: it is more than half the days of the month with water.
06 And if you go higher
All these figures are the city's, at 3,399 metres. As soon as you go up, the scale shifts downwards and does so fast: above 3,800 metres, June and July nights reach around five degrees below zero.
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And it works the other way too. The valley below the city, between 3,000 and 2,050 metres, is noticeably milder at night. When the city forecast looks alarming, it is worth remembering that half an hour's drive away there are several degrees of difference.
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Thomas Andy Branson