Almost nobody comes to Kathmandu for Kathmandu's weather. People come for what can be seen from Kathmandu, and for what can be done by leaving it. That is why the usual question — which month has the best weather? — does not work here. The mean daily maximum moves between 19.2 and 29.5 degrees across the whole year: ten degrees of range, none of them uncomfortable. What genuinely changes month to month is how many days the mountain range is visible.
01 The year moves ten degrees and fifteen hundred millimetres
The 1991–2020 normals measured at the airport give a mean daily maximum ranging from 19.2 °C in January to 29.5 °C in June. The mean minimum runs from 2.8 to 20.3 °C, so winter nights are genuinely cold but winter days are not. In temperature terms, Kathmandu is a comfortable destination all twelve months.
Rainfall is another story. The annual total is around 1,500 millimetres, but it is not spread out: it goes from 6.4 millimetres in November to 384.1 in July. Sixty times more. That is the axis the year turns on, and it is also what decides what you can see.
The four moments that define the year
6.4 mm over half a rainy day and a 23.6 °C high. Clean air, visible mountains and nights already cool.
43.3 mm over 3.8 days. The monsoon has just left and the air is washed; it is high season for a reason.
384.1 mm over 23.1 days. Constant low cloud: the range exists, but you cannot see it.
Barely any rain, but the air stagnates on the valley floor and the horizon dissolves into haze.
02 The monsoon takes almost eight of every ten litres
June, July, August and September add up to 1,176 millimetres, a little over 78% of the whole year. And it is not rain spread across isolated showers: in July and August it rains on 23 and 22.7 days respectively. The practical consequence is not getting wet, which a raincoat solves: it is that the sky is covered, and with a covered sky there is no mountain.
There is a second, less obvious and more annoying consequence: flights. A large share of the country's internal travel runs on small aircraft to mountain airstrips that operate on visibility alone. In monsoon season delays and cancellations stop being the exception and become the norm, and one day lost at the airport easily turns into three.
03 In November it rains half a day
November is, with the numbers in front of you, the roundest month of the year: 6.4 millimetres of rainfall spread over 0.5 rainy days, a mean maximum of 23.6 °C and a minimum of 8.4. That is, mild shirt-sleeve days, fleece nights and virtually no chance of rain changing your plans.
October comes right behind it and has an advantage of its own: it arrives immediately after the monsoon, with the atmosphere freshly washed and the valley still green. Its bill is 43.3 millimetres over 3.8 days and considerably more people, because it is the declared high season. If you can choose between the two, October gives better landscape and November better certainty.
Good weather here is not measured in degrees. It is measured in kilometres of horizon.
04 The other veil: winter in a closed valley
Here is the mistake people make reading only the rainfall column. January records barely 15.2 millimetres and December 7.8, so on paper winter looks as dry as November. And yet visibility gets worse, considerably so.
The reason is the shape of the place. Kathmandu sits on the floor of a valley closed by mountains at 1,400 metres, and in the cold months the air in the lower layers sits still instead of renewing itself. Everything emitted inside the valley stays inside the valley. The result is mornings of thick fog and days when the range, at exactly the same distance as always, simply does not appear.
05 What this means if you are going trekking
If Kathmandu is your starting point for walking in the mountains, the good window is the same: mid-October to late November, and secondly March to early May, when the air is worse but the cold at altitude is less harsh. The monsoon months are ruled out by mud, leeches and closed skies, and the deep winter ones by cold and snowed-in passes.
The year in one sentence: the temperature will never drive you away, but the sky can take from you exactly what you came to see. October and November are the answer, and November is the answer with half a day of rain in the whole month.
