Chiang Mai, the largest city of northern Thailand, sits in a valley of the Ping River, ringed by the forested mountains of the Thai highlands at around 310 metres above sea level and approximately 18.79°N, 98.98°E. It has a tropical savanna climate (Köppen Aw) — warm year-round — with three seasons: hot, rainy, and cool.

The hot season, from March to May, is the most punishing, with April the hottest month — highs around 36–37°C — under hazy skies. The southwest monsoon then brings the rainy season from May to October, with heavy afternoon and evening downpours, thick cloud and high humidity, greening the surrounding mountains; September is typically the wettest.

The cool season, from November to February, brings warm, dry, sunny days around 29–30°C and pleasantly cool nights that can drop to 13–15°C — chilly by Thai standards, thanks to the valley and the northern latitude. Rain is scarce and skies are clear; this mild, dry stretch is comfortably the best time of year.

Chiang Mai receives on the order of 1,100–1,200 mm of rain a year, concentrated in the monsoon from May to October, with a September peak, while December to February is nearly rainless — markedly drier than Bangkok or the southern Thai coasts. Live rainfall, humidity, and pressure readings for the city are shown in the panels above.

Chiang Mai's mountain-ringed valley traps a serious seasonal problem: from February to April, smoke from agricultural burning across northern Thailand and neighbouring countries settles in the basin, giving the city some of the worst air quality in the world for weeks at a stretch, until the monsoon rains finally clear the air.

To follow any single measurement in Chiang Mai more closely, use our live instruments: the online barometer for atmospheric pressure, the thermometer for temperature, the hygrometer for humidity, the anemometer for wind speed, the wind vane for wind direction, and the rain gauge for rainfall.