The weather you can expect when visiting Chiang Mai depends of course on the season. Chiang Mai’s climate can be roughly divided in three seasons, the rainy season, the dry and cool season, and the dry and warm season. Knowing these seasons will help you decide when are the best months to visit Chiang Mai.
First let's have a look at monthly temperature and rainfall. The following table shows high, mean, and low temperatures for each month in degrees Celcius (°C).
Over an entire year the average high temperature is 31.8 °C, the average mean temperature is 25.4 °C and the average low temperature is 20.1 °C
The next table shows the monthly precipitation, which generally means rain although an occasional hail storm may occur.
On average that is about 99 millimeter per month, but averages like this are not very useful. More important is to know that of the total 1185 mm of rain, about 87% falls between May and October.
Link : Beautiful Chiang Mai
4th AsiaEngage Regional Conference 2018, Chiang Mai University