Xian to Jiuzhaigou by bus

Hi. I would to find out if there is any direct bus from Xian to JZG in late October. I am thinking of taking bus as a alternative to flying, cos I read that flight wil be cancel if there is snowing.
BTW, l can only find bus from Mianyang/Jiangyou. And I don't think I want go JZG via Chengdu. Thanks for any advice.