# When Is Chiang Mai > When Chiang Mai URL: https://chiangmaibrief.com/guide/when-is-chiang-mai-burning-season/ Last-Modified: 2026-09-07 Author: The Chiang Mai Brief ## The short answer **February to April, peaking in March.** That’s the pattern, and it holds most years. If you want a single planning rule: assume March is bad, treat February and April as uncertain, and treat November to January as reliably clear. For the underlying causes and the protective measures, see our burning season hub [/air-quality-and-burning-season/ →](/air-quality-and-burning-season/) . This guide is about the calendar. ![A phone showing a red AQI reading against a smoky sky](/images/content/phone-held-up-showing-a-red-air-quality-index-read.webp) ## Month by month | Month | Typical air quality | What it feels like | | --- | --- | --- | | November | Excellent | Clear, cool, the best month of the year | | December | Excellent | Cool and clear, mountain views sharp | | January | Good | Still clear, occasional early haze late in the month | | February | Deteriorating | First smoke appears, some bad days by month end | | March | Poor to very poor | The peak. Extended runs of unhealthy readings | | April | Poor, improving | Hazy early, usually clearing after the first rains | | May | Good | Rains established, air washed clean | | June–October | Good | Green season. Rain keeps the air clear | The transition into the season is gradual and the exit is abrupt. Smoke builds over weeks; the first real storm clears it in a day. ## Why the dates move Three variables shift the timing year to year: **Rainfall timing.** The end of the season is essentially set by when substantial rain arrives. An early rain event in April ends it; a late one extends it into May. **Wind.** Still, cool mornings trap smoke in the valley. A windier year disperses more of it. **Regional burning intensity.** The smoke isn’t only local. Agricultural burning across northern Thailand, Myanmar and Laos varies with crop cycles, enforcement and economics. The reason all that smoke settles over the city rather than blowing through comes down to the valley’s shape, which we cover in why Chiang Mai’s air gets so bad [/guide/why-chiang-mai-air-gets-bad-basin-effect/ →](/guide/why-chiang-mai-air-gets-bad-basin-effect/) . That’s why you’ll find people who lived here for a year insisting March was fine and others describing the same month as unbearable. Both are telling the truth about different years. ![The same Chiang Mai viewpoint on a clear cool-season day](/images/content/same-chiang-mai-viewpoint-on-a-clear-cool-season-d.webp) ## The historical pattern In peak weeks, Chiang Mai regularly appears at or near the top of global air-quality rankings, with PM2.5 readings many multiples of World Health Organization guidance. Runs of consecutive days in the unhealthy range are normal in March. Outside that window the picture inverts completely. From May through January the city’s air is unremarkable and frequently good, which is the part that never makes the international news. Both facts are true simultaneously, and holding both is the key to planning sensibly around it. ## Planning implications **Visiting.** November to February is the window. If you can only come in March, come with realistic expectations and an indoor-heavy itinerary. **Living here.** Decide your March strategy in January, not in March. Whether that’s leaving, buying a purifier, or simply cancelling outdoor plans, deciding early is much cheaper than improvising. **Booking flights out.** If you plan to escape, book early. A lot of Chiang Mai residents leave in the same three weeks and prices reflect it. **Long leases.** Factor in that you’ll pay rent for a month you may not be here. Some people negotiate this; most absorb it. For the wider seasonal picture — including when the festivals fall and what green season is actually like — see our guide to Chiang Mai’s seasons and when to visit [/guide/chiang-mai-seasons-when-to-visit/ →](/guide/chiang-mai-seasons-when-to-visit/) . Got questions? ## Common questions Which month has the worst air in Chiang Mai? March, in most years. The February to April window covers the season, but March is consistently the month with the highest PM2.5 readings and the longest run of unhealthy days. Some years the worst weeks land in late February or early April instead. How long does burning season last? Roughly six to ten weeks of genuinely poor air, within a wider February to April window. The variation between years is substantial — a wet, windy year can be much shorter and milder than a dry, still one. Is April safe to visit? It depends on the year. The air usually improves once the first substantial rains arrive, typically mid-to-late April, and clears quickly after that. Early April is often still hazy, and it is also the hottest part of the year. Late April is a coin toss that has been going the right way more often than not. More in this area ## Related guides Comparison ### Best Air Purifiers for Chiang Mai (HEPA Buyer Guide) Choose an air purifier for Chiang Mai's smoke — HEPA H13/H14 and CADR explained, Xiaomi, Coway, Levoit and Blueair compared, and room sizing. 7 min read [Best Air Purifiers for Chiang Mai (HEPA Buyer Guide) →](/guide/best-air-purifiers-chiang-mai/) Step by step ### How to Check AQI & PM2.5 in Chiang Mai Monitor Chiang Mai air quality reliably — IQAir vs Air4Thai, reading PM2.5, what the numbers mean and setting alerts. 5 min read [How to Check AQI & PM2.5 in Chiang Mai →](/guide/how-to-check-aqi-pm25-chiang-mai/) Common concern ### Sealing Your Room & Staying Indoors Safely Practical steps to reduce indoor smoke exposure in Chiang Mai — sealing your room, positive-pressure setups, N95/KN95 masks and safe venues. 5 min read [Sealing Your Room & Staying Indoors Safely →](/guide/sealing-your-room-staying-indoors/) Decision guide ### Should You Leave Chiang Mai During Burning Season? An honest framing of the stay-or-go decision for Chiang Mai's burning season — health risk factors, the cost of leaving, and who should go. 5 min read [Should You Leave Chiang Mai During Burning Season? →](/guide/should-you-leave-during-burning-season/)