Chiang Mai Cool Season
(late October to end of February). average temperature 21C / 70F and much cooler at night. The coldest months are December and January.
Chiang Mai Hot Season
(early March to end of May) Average temperature 30C / 86F. The hottest month is April.
Chiang Mai Rainy Season
(early June to early October). Average temperature 26C / 78F. The wettest month is September.
The Rainy Season usually starts with intermittent late afternoon and evening thunderstorms. These typically last about an hour or so, however, some are longer. New weather patterns are forming with Global Warming and a significant increase of Rain is not surprising. Thunder, lightning, and tropical downpours may be a little intimidating and frightening but they can also be entertaining. There can be periods of a week or so without any rain. Late-August to mid-September is the peak Rainy Season.