Kathmandu weather in September

Regulars are specific that the real discomfort this month comes indoors rather than out - hotel rooms often lack heating, so an extra blanket, hot water bottle or even a sleeping bag liner gets recommended almost as often as warm outdoor layers. Our row backs the cool, dry, sunny read, 19.6C over 5.7C nights feeling 5C, with rain minimal at 17.7mm across 3.5 days and snow in the valley itself called a genuine rarity, just a handful of recorded instances over the past century. Regulars are consistent the days themselves are pleasant and clear, valued as one of the least crowded times to visit, though winter haze and air pollution in the valley are a real and separate concern from the cold. The record: humidity 75 percent, 9.1 hours of sun, a 6.3 kph wind and AQI 123.

Regulars describe February here as three different temperatures depending on where you stand: warm enough for a t-shirt in direct sun, noticeably cool in shadow or indoors, and properly cold once night falls, though it seldom actually freezes. Our row backs the range, 21.6C reading as 20C over 7C nights feeling 6C, with 45.9mm of rain across 7.3 days and a trace of snow, 0.3cm. Mornings often start foggy and clear by mid-morning into a fine day. The pollution question comes up constantly on this board, and the pattern they describe is a daily one rather than seasonal: relatively clear until seven or eight, worsening once traffic builds through the day - our AQI of 109 is the average across that whole cycle. The record: humidity 71 percent, 9.8 hours of sun, a 7.7 kph wind.

Regulars choose March over April for one reason: the haze. Agricultural burn-off across northern India and the Terai begins around late February and worsens steadily towards April, and humidity rises through March as well, so the mountain views soften as the season goes on. One year March was the clearest in memory and April lost the mountains entirely. From the valley floor the views are already scarce; for sharp ones you climb to four or five thousand metres. March is colder than April and slightly drier, and mid-March is the trekking window. Our AQI of 96 is that burn-off measured. The record: 25.7C over 11.1C, 60.4mm across 11.7 days and 10.6 hours of sun.

November is the month Nepal regulars name first, and the reason is visibility: this is post-monsoon, the driest and least humid of the autumn months, with the least cloud, so the mountain views are clear and sharp and the leeches are gone. Kathmandu itself they describe as pleasant by day and genuinely cold morning and evening - their 12 to 18C days and 5 to 8C mornings sit below our row's 23.3C and 9.8C, so read theirs as the shaded valley in early winter. Thin gloves and a scarf for the ends of the day is their packing note. The cost is company, because this is the busiest trekking season of the year. Our row adds AQI 106, the valley's winter air. The record: 5.4 precipitation days carrying 18.5mm and 9.7 hours of sun.