I have been a regular visitor to Chiang Mai, spending up to six months, the UK's winter months, here every year for 12 years. I love CM. But this year I am going home at the end of February instead of early April to avoid the seriously damaging aq in March and April. Even being here in February is looking unwise. No Travel Agent in the world is going to risk its reputation by sending customers to SE Asia during the smog season. If you take out the rainy season and the floods in October, that leaves November, December and January as the only sensible months to visit Thailand. And the way things are going with the smoke, you can soon take out January too. Leaving two months smog, flood and rain risk free.