Chiang Rai — sää kuukausittain

Chiang Rai's own forum describes June as a month of two halves: the first couple of weeks tend to be pleasant with only occasional storms, then the rainy season properly sets in for the back half, bringing heavier downpours and the odd night where it rains straight through. Even so, one regular visitor noted that in a typical June trip only a handful of days actually forced a change of plans to something indoors - most days still get some sunshine between showers. Nights cool to the mid-20s C, which is a welcome break after a hot, humid afternoon.

December is northern Thailand's clean window, and that is the strongest argument for it. The record puts Chiang Rai's air at AQI 55 in December, against 106 in March and 113 in April, when agricultural burning peaks. The forum's timeline matches: some haze exists from December onwards, but the heavy stuff — whole hillsides alight, the region choked — runs from late February into late April. Weather-wise December is dry and bright, mid-to-upper 20s by day and 15–18 at night. One practical note regulars give: very few Thai hotels have heating, and December nights up here are cool enough to notice.