Due to its high elevation in the mountainous north, the climate and weather in Chiang Mai differ considerably from southern regions in Thailand. It is cooler, less humid and at night temperatures during the cold season can make you reach for your jacket.
The south-west Monsoon arrives end May marking the start of the cool season lasting until November. The minimum temperature then is approximately 21 degrees Celsius with the maximum being approximately 32 degrees Celsius. The most rain is experienced during August and September with an average precipitation of 250 mm. Though not as tropical as other parts of Thailand, wet months does not mean endless rain. Mornings are generally clear, afternoons wet and and occasional evening showers.
Mid November until early May is the dry period due to the north-east Monsoon blowing in from Vietnam and China, providing six months of sunny skies and the best time in Chiang Mai to miss the rain. Temperatures during this time however can drop as low as 13 degrees Celsius in January rising steadily with a minimum temperature of 22 degrees Celsius in April. The Maximum temperature during this time reaches anything from 28 degrees Celsius in December to 35 degrees Celsius in April.
This is a good time to visit the region if you prefer moderate temperatures with less rain. March to late May is hot and sees temperatures from 30 to 40 degrees Celsius. Naturally, being a mountainous area, weather can at times be slightly unpredictable. Come prepared for any conditions when you visit, especially during the wet and cold season.