The weather of Northern Thailand, including Chiang Mai, differs from the traditional divisions of spring, summer, autumn and winter. Instead, the region has three distinct seasons: the cool season, hot season and rainy season. Chiang Mai is known as the ‘cool capital’, and in comparison to the sweaty heat of Bangkok, the climate is far more agreeable.
Cool season in Chiang Mai
The most popular time for visiting Chiang Mai (weather wise) is the cool season, which runs from December to the end of February. It is in fact pleasantly chilly in the evenings, and if you are planning on visiting Chiang Mai at this time of year, it would be wise to bring all-weather gear along; particularly if you intend hiring a motorcycle to get around, or going on a mountain trek. However, don’t leave out your summer clothes, as midday temperatures can climb well into the 30s (Celsius).
Try to avoid a holiday to Thailand during this time (April-June) as unless you are completely accustomed to tropical heat, you will find the humidity utterly draining. Despite all the moisture in the air, however, there is virtually no rain during this period. The lack of water with blazing heat and slash-and-burn agricultural practices causes the usually lush green jungle that covers the surrounding hills to turn a charred brown from fires that burn almost constantly from January until the rains arrive. Not only does this affect the vegetation, but a trademark ‘hot season haze’ hangs over the entire city, obscuring the beautiful vistas.
The weather starts heating up in Chiang Mai around early February, and by mid-March, the nippy nights of December are nothing but a pleasant memory, with daytime maximums regularly reaching 40°C.
Rainy season in Chiang Mai
The southwest monsoon usually arrives from India at the end of May, and from then until November the weather in Chiang Mai and northern Thailand is very wet. The rainy season is characterized by torrential downpours, but they tend to be sudden bursts that only last for an hour or so rather than a steady stream of water.
Although mosquitoes are rife during this time, the rainy season is otherwise a pleasant time to visit the north. The rains bring respite from the heat, and the landscape returns to its strikingly-gorgeous shade of green. Rainfall is usually heaviest in September, with an average precipitation of 250mm.
Murky March health hazards
Chiang Mai has a particularly chronic problem with burning (and resulting haze) in March. The mountain views disappear as the Ping River valley chokes under a dusty haze that can often be a health hazard. This is the result of indiscriminate burning by ill-educated peasant farmers, couple with stagnant breeze-less weather. Authorities have failed in recent years to tackle the issue, as tourists are advised to stay away and locals remain indoors on days when the dust particle levels far exceed accepted international health thresholds.
Generally speaking, the weather of northern Thailand is far more temperate than central or southern Thailand. The area is more than 2,000kms from the equator and much closer to the Tropic of Cancer. This, coupled with its mountainous terrain and location in the Asian interior, brings cooler temperatures and less humidity. However, there is still quite a bit of precipitation during the rainy season and the weather gets very chilly once you leave Chiang Mai and head up into the mountains.
Chiang Mai weather by month
January is a very popular month to visit the North as it experiences Thailand’s coolest weather, making Chiang Mai and the mountains a novelty with Thai tourists. Expect temperatures similar to a sunny European summer day, somewhat hazy, and chilly at night.
The weather and temperatures are still very agreeable in Chiang Mai in February, though it still gets quite hot around midday in the valleys. It never rains, but by now the landscape is quite dry and the vistas hazy. Tourist services remain busy.
March is one of the worst times to visit Chiang Mai (weather wise), since the air is thick with dust and micro-particles from widespread rural burning. The haze removes any view of the mountains, there’s no breeze, and the results can be a health hazard on certain days.
The weather in Chiang Mai gets very hot in April as temperatures peak in the mid 30s (Celsius); the rain has yet to cool the region down and the landscape remains dry. A popular reason to visit is the annual Songkran water splash festival, which is best enjoyed in Chiang Mai – hotels fill up by mid-month.
From May onwards the tourist season in Chiang Mai and Northern Thailand is in decline, but the weather improves as the rains arrive. This means sunny skies and afternoon storms to cool things off.
It’s still hot in June in Chiang Mai as the weather moves into the full rainy season, bringing with it 90 per cent humidity, adding to the immense feeling of warmth. It’s still cooler than Bangkok and the South.
July is low season in northern Thailand; cloud cover in the rainy season cools the weather in Chiang Mai but you also get plenty of sunshine in between the showers. It remains hot, though could be cloudy and warm for days. Room rates are cheaper, tourist numbers far less, but the experience is just as pleasant.
Mainly backpackers come to Chiang Mai in August, while most other tourists prefer more northern summer destinations around the globe. This means the budget travellers get out-of-season deals, see the province when it’s at its lushest and still get plenty of sunshine… even if it’s humid and sometimes cloudy!
September is one of the quietest months for tourism in Chiang Mai and usually the wettest weather. Expect showers almost every day, along with cloud cover (but warm temperatures), a good chance of sunshine, and high humidity. Best bargains on prices this month.
October is one of the prettiest times to visit Chiang Mai and Northern Thailand, at the tail end of the wet weather when the rice fields create a patchwork of green across the landscape. It might still rain regularly but remains mostly sunny and begins to cool and become less humid. However, there are few tourists to enjoy this.
Prices jump up from early November as the tourist season gets going and the weather dries up, with sunny skies, cooler days and the lush remains of six months of rain. It’s one of the best times to visit, not quite busy yet but some of the best weather, with clear views of the mountains.
December is probably the busiest month for tourism in Chiang Mai and northern Thailand in general as local Thai tourists make the most of the cool weather. Expect full hotels and busy roads during long weekends – especially in Pai – but nice clear mountain views, chilly evenings, and sunny skies.