Is there any month when the whole country has good weather?

No. January and February are the closest you get, with the Andaman coast dry and the Gulf coast turning dry by February. But Chiang Mai is in burning season by February, so the north is already compromised. You have to choose a region per month.

Can I visit Chiang Mai in March and just wear a mask?

You can, but the PM2.5 daily average runs 80 to 250 µg/m³, five to sixteen times the WHO safe limit of 15 µg/m³. A mask helps but does not eliminate the risk. A traveler we know stayed through March 2018 thinking warnings were exaggerated and left in 2023. It is not a vacation most people enjoy.

When is the cheapest time to visit Chiang Mai?

May through October. Accommodation is 30 to 50 percent cheaper than high season. Flights from Bangkok can drop to 800 to 1,500 THB one way. The trade off is humidity of 75 to 90 percent and daily rain.

Is Songkran in Chiang Mai worth the bad air?

Worth doing once. Skip a second time. The water throwing runs 13 to 15 April annually, often starting 12 April, and can stretch three to seven days. The air is hazardous that entire period. If you have not seen it, one trip is enough.

Which coast is better in November?

The Andaman coast. November is the start of its dry season. The Gulf coast is still under the northeast monsoon and getting heavy rain. If you want sun in November, go to Phuket or Krabi, not Koh Samui.

Best Time to Visit Thailand: Month-by-Month

Two Monsoons, One Burning Season and a Few Perfect Months

The biggest mistake travelers make about Thailand is thinking there is one good season for the whole country. There is not. The southwest monsoon drowns the Andaman coast from May to October while the Gulf of Thailand stays mostly dry. Then the northeast monsoon reverses it, soaking the Gulf from November to January while the Andaman side cleans up. Layer the Chiang Mai burning season on top of that, roughly February to April, and you get a country where every month is bad somewhere but a few months are excellent in specific places. The real insight is timing a region, not the whole country.

Here is how the two monsoons and the northern agricultural burning actually overlap. The southwest monsoon runs June through October. It slams into Phuket, Krabi, Khao Lak, and the rest of the Andaman coast with heavy daily rain and rough seas. During the same months, Koh Samui, Koh Phangan, Koh Tao, and the Gulf coast see only sporadic showers, with September being the wettest month on that side. The northeast monsoon flips the pattern from November through January, pushing rain onto the Gulf while the Andaman coast enters its dry season. That leaves January and February as the only two months when both coasts are reliably dry. If you want beach time and you want options, those two months are your window.

Thailand rainy season street — Takeaway , CC BY-SA 3.0 via Wikimedia Commons

The Burning Season Overlay: Chiang Mai from February to April

While the coasts are sorting out their monsoons, northern Thailand hits its burning season. The months are February to April, with March and April as the peak. Agricultural smoke from the Mae Hong Son loop and beyond turns the air hazardous. The PM2.5 daily average in peak months runs from 80 to 250 µg/m³. The World Health Organization 24 hour guideline is 15 µg/m³. You are breathing five to sixteen times the safe level on a typical March afternoon.

Here is the concrete failure case. A traveler we know stayed through March 2018 thinking air quality warnings were exaggerated. She left that year and again in 2023. That is the pattern: the burning season is not a theoretical risk. It is a reason to leave. If you are in Chiang Mai between February and April, the normal route is to get out. Book a flight to the Andaman coast or the Gulf. The 2025 low season one way Bangkok to Chiang Mai fare ran 800 to 1,500 THB on Nok Air and AirAsia, so the reverse trip is cheap.

Do not mistake the burning season for the hot season. The hot season runs February to May with daytime highs of 35 to 40°C. The wet season runs June to October with highs of 30 to 34°C and humidity from 75 to 90 percent. The cool season is November to January, with daytime highs of 28 to 32°C, nights dropping to 12 to 16°C, and humidity between 50 and 65 percent. That cool season is the only window in Chiang Mai where you get both comfortable temperatures and breathable air.

What This Means for Your Trip Plan

If you want the north and the beaches in one trip, you have two narrow windows. January to February works for both coasts and for Chiang Mai cool season. That is your best shot. November to December works for the Andaman and Chiang Mai but the Gulf coast is wet. March to April works for the Andaman and the Gulf but Chiang Mai is on fire. There is no month where the whole country is good. Pick a region per month or accept a compromise.

Chiang Mai in the Cool Season: November to January

This is the only period where Chiang Mai is comfortable and safe to breathe. Daytime temps run 28 to 32°C. Nights drop to 12 to 16°C, and you will want a jacket for evening markets. Humidity stays low at 50 to 65 percent. Doi Inthanon summit can hit 0 to 8°C overnight with frost possible. Doi Suthep temple costs 30 THB entry. Doi Inthanon National Park costs 300 THB for foreigners. Both are worth the trip in cool season. Skip them in hot season and burning season. The view is not worth the heat or the smoke.

Chiang Mai in the Burning Season: February to April

You should not be in Chiang Mai during these months unless you have an unbreakable commitment. The air is dangerous. PM2.5 hits 80 to 250 µg/m³ daily average. That is not a haze day. That is a health advisory day. If you are stuck here, limit outdoor activity, run an air purifier indoors, and wear an N95 mask outdoors. Plan your escape. The cheapest accommodation in Chiang Mai runs from May to October, with discounts of 30 to 50 percent versus high season. That tells you what the market thinks of burning season: it is not high season, it is the season to leave.

Songkran in Chiang Mai: 13 to 15 April

Songkran, the Thai New Year water festival, falls right in the burning season peak. In Chiang Mai the water throwing lasts three to seven days, often starting 12 April. It is worth doing once. Skip a second time. The combination of hazardous air and being soaked for days is not a vacation most people repeat. If you want the festival, book a room in the old city early and budget for an air purifier in your hotel. If you have done it once, consider celebrating Songkran on the Andaman coast instead, where the air is clean in April.

Monthly Climate and Air Quality by Region

Month	Andaman Coast	Gulf Coast (Samui, Phangan, Tao)	Chiang Mai
January	Dry	Wet (Northeast Monsoon)	Cool, clean air
February	Dry	Dry	Cool start, burning begins late
March	Dry	Dry	Burning season peak, hazardous air
April	Dry	Dry	Burning season peak, hazardous air
May	Rain begins	Dry	Hot, burning ends, rain starts late
June	Heavy rain	Dry	Wet, humid
July	Heavy rain	Dry	Wet, humid
August	Heavy rain	Dry	Wet, humid
September	Heavy rain	Wet peak	Wet, humid
October	Heavy rain	Wet	Wet, humid
November	Dry begins	Wet	Cool, clean air begins
December	Dry	Wet (Northeast Monsoon)	Cool, clean air

Thai beach dry season — Petty Officer 1st Class Melissa Russell , Public domain via Wikimedia Commons

What it Costs and How to Move

Domestic flights tell you the season as clearly as any weather chart. The 2025 low season one way Bangkok to Chiang Mai fare on Nok Air and AirAsia ran 800 to 1,500 THB. High season ran 1,500 to 3,500 THB. That gap is your signal: low season is May to October, when the rain and humidity keep tourists away. High season is November to January and parts of February, when the cool season draws everyone north.

Accommodation follows the same curve. Cheapest months in Chiang Mai are May to October, with discounts of 30 to 50 percent versus November to January. If you can tolerate humidity and afternoon rain, May and June are the bargain sweet spot. September is the wettest month across much of Thailand. That is when you get the deepest discounts but also the highest chance of travel disruption from flooding, especially in the north and on the Andaman coast.

Visa Rules and the Chiang Mai Immigration Office

Visa rules are simple for most Western passports. The tourist visa exemption gives you 30 days as of 2025, set by the Thai Immigration Bureau. If you need more, extend by 30 days at any immigration office for 1,900 THB. The Chiang Mai Immigration office is at 71 Moo 3, Sanambin Road, T. Nong Han, A. San Sai. Hours are 08:30 to 16:30, Monday to Friday. Arrive early. The queue fills fast.

Who This Suits and Who it Does Not

This page suits the traveler who wants to understand the trade offs: the beach person who can pick a coast by month, the northern trekker who knows to arrive in November and leave by February, the budget traveler who will tolerate rain for 50 percent off a room. It does not suit the traveler who wants one perfect month for the entire country. That does not exist. It does not suit the traveler who thinks a mask solves the burning season. It does not. And it does not suit the traveler who books a two week trip to Thailand in March without checking which region matches their plans. The single thing that most often goes wrong here is showing up in Chiang Mai in March expecting clear skies, because the weather websites do not show PM2.5 on the temperature chart.