Chiang Mai has three clear seasons: cool and dry from November to February, hot and hazy from March to April, and rainy from May to October, with the heaviest rain in August and September. January has the coolest nights, with an average low of 15.7 °C, and April the hottest days, with an average high of 36.7 °C.
Those figures are 30-year averages (1991–2020) published by Thailand's weather service, the Thai Meteorological Department or TMD, for its Chiang Mai station, index 48327, at 305 meters in the city near the airport. They show what a typical year looks like rather than a forecast, and they are for the valley floor: the mountains around the city are much colder. Check the TMD forecast before you travel.
For the country as a whole, region by region, see our page on Thailand's weather month by month. This page stays in Chiang Mai; our Chiang Mai city guide covers everything else.
Chiang Mai climate at a glance (TMD, 1991–2020)
- Rain in a year
- 1,139.2 mm on about 119 days
- Driest month
- February (9.6 mm on 0.9 days)
- Wettest month
- August (223.3 mm on 20.9 days), then September (207.2 mm)
- Hottest month
- April (average high 36.7 °C)
- Coldest nights
- January (average low 15.7 °C); December 16.9 °C
- Haze
- About 116 days a year, most from January to April; peak March
- Forecasts
- Thai Meteorological Department, hotline 1182
Chiang Mai's twelve months in numbers
Below are the average daytime high and night-time low, monthly rainfall, how many days bring rain, how many days the station logged haze, and hours of sunshine. In TMD's count, 0.1 mm is enough to make a rainy day, so a brief shower at dusk weighs the same as a whole wet day.
| Month | Day / night °C | Rainfall (mm) | Days with rain | Haze days | Sunshine (hours) |
|---|---|---|---|---|---|
| Jan | 30.0 / 15.7 | 11.3 | 1.3 | 18.7 | 258 |
| Feb | 32.9 / 16.8 | 9.6 | 0.9 | 22.1 | 252 |
| Mar | 35.4 / 20.1 | 20.4 | 2.8 | 26.8 | 268 |
| Apr | 36.7 / 23.4 | 54.3 | 6.8 | 17.1 | 253 |
| May | 34.7 / 24.2 | 167.5 | 14.8 | 1.5 | 217 |
| Jun | 33.2 / 24.5 | 118.2 | 16.3 | 0.0 | 146 |
| Jul | 32.1 / 24.3 | 148.6 | 18.8 | 0.0 | 115 |
| Aug | 31.6 / 24.0 | 223.3 | 20.9 | 0.2 | 111 |
| Sep | 32.0 / 23.7 | 207.2 | 18.1 | 1.3 | 153 |
| Oct | 31.7 / 22.6 | 123.8 | 11.8 | 6.7 | 196 |
| Nov | 30.8 / 19.9 | 40.9 | 4.2 | 7.8 | 229 |
| Dec | 29.2 / 16.9 | 14.1 | 1.8 | 13.5 | 238 |
Three things stand out. Daytime highs stay around 29 to 37 °C all year, so even in the cool season the afternoons are warm; it is the nights that change. The dry months really are dry, with almost no rain from December to February. And the haze column is almost the mirror image of the rain column: as soon as the rains start in May, the haze disappears.
November to February: the cool season
Most visitors come in these months, and it is easy to see why. From December to February it hardly rains, the sun shines for more than 230 hours a month, and nights fall to around 16 to 17 °C in December and January. Daytime highs are still about 29 to 33 °C, so you will be in a T-shirt by lunchtime.
Cold nights are relative. A mean low of 15.7 °C in January is mild by European or North American standards, but it feels cold in an open-air restaurant or on a scooter at night. The lowest temperature at the station in those 30 years was 3.8 °C, in a December; claims that Chiang Mai "drops to 5 °C most winter nights" are not supported by the averages. Pack one warm layer, long trousers and closed shoes. TMD also logs a few foggy mornings a year, between November and January.
The mountains are another matter. On Doi Inthanon, Thailand's highest peak, ground frost can form near the summit on the coldest mornings. TMD has no station on the mountain, so we have no official averages for it. Frost is not snow, and there is no official record of snow in Thailand; our page on whether it ever snows in Thailand has the details.
March and April: heat and the smoke season
March gets more sunshine than any other month, about 268 hours, and April the hottest, with an average high of 36.7 °C. The highest temperature in the 30-year table was 42.5 °C, recorded in a May. Nights stay above 20 °C from March, so the cool season is clearly over.
These are also the haziest months. The station records haze on 26.8 of March's 31 days, and on most days from January to April. That haze is largely smoke from burning in the region, and its health effects are the subject of two other pages: our article on Chiang Mai's smoky season explains the causes, and our guide to PM2.5 air pollution in Thailand covers air-quality readings and how to protect yourself. If you have asthma or a heart or lung condition, read both before you book a trip for February to April.
The clearest skies and the haziest skies are only weeks apart. December and early January are usually bright and dry; by February and March the same view across the valley can disappear into a grey-brown haze. If clear air matters to you, aim for November to mid-January.
May: the rain comes earlier than people think
Many websites say Chiang Mai's rainy season runs from June and that May is still dry. The averages say otherwise. May brings 167.5 mm of rain on almost 15 days, more rain than June (118.2 mm), and it averages 6.5 days with thunder, the most of the year. The first storms clear the air quickly: haze days drop from 17 in April to under two in May.
May storms tend to be short, building up after a hot morning and breaking later in the day. Plan outdoor sights for the first half of the day.
June to October: the rainy season, peaking in August
The wettest month is August, with 223.3 mm on 20.9 days, followed by September with 207.2 mm. July, often called the wettest month, averages 148.6 mm. Sunshine falls to about 110 to 115 hours a month in July and August, under four hours a day. The station's wettest day in the 30-year table, 144.4 mm, was in a September.
The rainy season is not a write-off. Showers alternate with dry spells, the hills turn green and the waterfalls are at their fullest, but trails get muddy and some are closed: the Kew Mae Pan trail on Doi Inthanon shuts every year from 1 June to 31 October. October is a transition month, with less rain (123.8 mm) and nights starting to cool. What wet-season travel is really like, and how to plan around it, is covered in our guide to Thailand's rainy season.
For comparison, Chiang Rai is cooler and wetter than Chiang Mai: its TMD station averages 1,723.5 mm of rain a year, with 372.9 mm in August, and a January average low of 13.8 °C.
Festival weeks that fill the hotels
The weather is not the only thing that decides when rooms run out. Two events in the cool season bring very large crowds:
- Yi Peng, the northern lantern festival, falls in November with Loy Krathong. In 2026 the city's festival runs from Monday 23 to Wednesday 25 November. The rules on sky lanterns and where the ticketed events are held are explained in our Yi Peng festival guide.
- The Chiang Mai Flower Festival is held in early February, but not always on the first weekend: in 2026 it ran from 13 to 15 February. No date for 2027 had been announced as of 9 November 2026. Our page on the Chiang Mai Flower Festival has the background.
Both fall in the dry season, when Chiang Mai is already busy. Book early for those weeks, and for Christmas and New Year. The old city, Nimman and the riverside are compared in our Chiang Mai accommodation guide.
The best time to visit Chiang Mai
On the averages, November to mid-January is the strongest period: little rain, plenty of sun, cool nights and, usually, clean air. February is still dry but hazier. March and April are the months to avoid if you are sensitive to heat or smoke. From May to October you trade rain for green hills, fewer visitors and clear air. To compare Chiang Mai with other places for your own dates, try our best time to visit tool.
Frequently asked questions
What is the coldest month in Chiang Mai?
January. The Thai Meteorological Department's 1991–2020 average low for the Chiang Mai station is 15.7 °C in January and 16.9 °C in December. Daytime highs are still around 29 to 30 °C, so it is the nights and early mornings that feel cold.
Which month has the most rain in Chiang Mai?
August, with an average of 223.3 mm on 20.9 days, followed by September with 207.2 mm. July, which is often named as the wettest month, averages 148.6 mm. May is already wetter than June.
Is December a good time to visit Chiang Mai?
Yes, for most travelers. December averages only 14.1 mm of rain, on under two days, with about 238 hours of sunshine and nights around 17 °C. It is also one of the busiest months, so book rooms and tours early, especially around Christmas and New Year.
When is the smoke season in Chiang Mai?
Mainly January to April, with the worst haze in March, when the TMD station logs haze on almost 27 of 31 days. The rains in May usually clear the air. For health advice, see our pages on the smoky season and PM2.5.
Do I need a jacket in Chiang Mai?
From November to February, bring one warm layer for evenings, early mornings and scooter rides; nights can drop to 15–17 °C. For the mountains, such as Doi Inthanon, bring a proper warm jacket, as it is much colder at the top.
Sources
- Thai Meteorological Department – Climatological data for the period 1991–2020, Chiang Mai (48327) and Chiang Rai (48303) stations (checked November 2026)
- Thai Meteorological Department – Weather forecasts (checked November 2026)
- Chiang Mai News – Yi Peng 2026 planning meeting (23 September 2026; checked October 2026)
- Sor Wor Por FM91 (LINE Today) – Kew Mae Pan trail season (1 November 2025; checked November 2026)
- Tourism Authority of Thailand – A survivor's guide to winter in northern Thailand (6 January 2026; checked November 2026)