Some questions about Kam Muang Thai?

Can someone please explain this to me? It's a dialect of standard Thai, correct? Wikipedia almost made it sound like a whole different language, so I'm not really sure. How widely spoken is it in northern Thailand? What are the differences between it and standard Thai? I'm moving to northern Thai in August, so should I continue to study standard Thai, or would that not be a good idea? Are there any other dialects in northern Thailand that I should be aware of? Any help is greatly appreciated :)