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).

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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.

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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.

Based on the above tables, the temperature and rainfall graphs for Chiang Mai look like this:

Some average climate data for Chiang Mai

Let's summarize Chiang Mai's climate by looking at some averages and some extremes:

Temperature
Average temperature throughout the year	25.4 °C
High temperatures (daytime)
Average high temperature	31.8 °C
Highest monthly mean high temperature (April)	36.1 °C
Lowest monthly mean high temperature (January)	28.9 °C
Low temperatures (night)
Average low temperature	20.1 °C
Highest monthly mean low temperature (June)	23.7 °C
Lowest monthly mean low (January)	13.7 °C
Days with frost	0 days
Temperature range
Average temperature range (day-night)	11.5 °C
Highest temperature range (January)	15.2 °C
Lowest temperature range (August)	7.7 °C
Rainfall
Total yearly rainfall	1185 mm
Average monthly rainfall	99 mm
Days with more than 0.1 mm rain	109
Driest month (January)	7 mm
Rainy days in driest month	± 1 day
Wettest month (August)	236 mm
Rainy days in wettest month	± 18 days

Seasons in Chiang Mai

Chiang Mai has six wet months (May-October) which can be called the rainy season. During these wet months the weather is relatively warm and air humidity is high (30-65%). This wet weather is caused by the south-west monsoon, which usually arrives from India during the month of May. Most rain can be expected during August and September.

The other six months (the north-east monsoon) may be called the dry season, but within this dry season you can distinguish a cooler period (November-February) and a warmer period (March-May). Throughout the dry seasons the air humidity is relatively low (5-25%).

Compared to the central and southern parts of Thailand, Chiang Mai is slightly cooler and enjoys a lower relatively humidity. It is especially this lower humidity which contributes to the nice climate in Chiang Mai.

Note that especially during December and January, which you could call the Chiang Mai winter, the evenings are very cool and you will need some warm clothes during this period. A sweater or jacket will be needed after sunset, but during daytime you can walk around in shorts and t-shirts.

When to visit Chiang Mai

If you enjoy a rainy holiday, just come in August or September and you will get what you deserve. Most people however will opt for the Chiang Mai winter season and enjoy the dry and slightly cooler weather. The best months to visit are probably from October to January.

During October-November you still may get some rain, but the advantage is that so soon after the rainy season everything is still green and clean and the many waterfalls near Chiang Mai are still with a lot of water. December and January have excellent weather, warm during the day and cool during the evening and night. You will need a sweater or jacket after sunset. Towards the end of February and in March temperatures are going up, and as it has not rained for several months the environment gets rather dry and it can be quite dusty.

From January to April, Chiang Mai often suffers from air pollution caused by forest and bush fires, but also because farmers tend to burn their old rice fields in preparation for the new season. All these fires cause a lot of smoke and dust, which probably make March and April the worst months to visit Chiang Mai. Sometimes this smog starts already in February or even January and it can last longer if rains come late.

April dry and usually very hot, but a visit during the middle of April is still worthwhile as you can enjoy the yearly Songkran festival, which celebrates the Thai New Year. The monsoon rains usually start in May, reaching their peak during August and September. With the monsoon rains, the sky gets cleaner as all the smoke and dust is washed out or blown away.

Note: The above climate data for Chiang Mai were compiled from a number of sources. Each source gives slightly different figures. Differences depend on the exact location of where the data were collected, and also the period over which the average was calculated. Climate Change is of course another contributing factor. Don't quote the above data but just use them to get an idea of the climate in Chiang Mai. Weather will change from year to year anyway.