I'm visiting Thailand from mid-Feb to mid-March of 2014. Will probably spend at least 2 weeks north of Bangkok before heading south, and would like to devise a rough itinerary for that period. Initially I ruled out the north and northeast and decided to focus on the central regions, because I read that the smoky haze can start to get serious in the north around late Feb/early March.
In your experience, is this generally the case? Are some parts of the north/northeast less affected? Does the haze extend into central Thailand as well? For instance ... Sukhothai? Kanchanaburi/Sanklaburi? Khao Yai NP? Thanks!
Sukhothai should be ok as it's a good 4 hours from Chiang Mai . Kanchanaburi is west of Bangkok which is a long way from the north.
March is a very hot month. I've been to Chiang Mai in March and while it was hazy it wasn't that bad, it's the heat which is more of a concern but I found Koh Samui to be hotter.
I think you should plan your trip around your interests rather than worry about haze.
The Kanchanaburi-Sangkhlaburi area is nice. In between you have Sai Yok which is a good place to stay on the river.
Khao Yai NP is best done in Dec/Jan when the Elephants are more likely to be active in winter time. The waterfalls will be dry around March also.
Feb/March is a good time to do the Andaman coast because the tigerline ferries operate and you can island hop.
There's no way to predict the haze situation a year in advance and based on specific locations. Anywhere around and north of Bangkok can have air quality issues especially late Feb through March depending on how much / where agricultural burnoff is happening and if/when/where there has been any decent wind/rain to clear it out. Here in Chiang Mai, for example, we had a nice rain last night and today is pleasant. Meanwhile a couple days ago it was kinda hazy and quite hot. Tomorrow is another day. Check PM-10 levels on http://aqmthai.com a few days before you go.