Bus transportation to Songpan at the beginning of February

I plan to go from Chengdu to Jiuzhaigou by bus at the beginning of February and make a stopover at SP to see Mounigou valley. After visiting Jiuzhaigou park I plan to take a flight back to Shanghai (via Chengdu). I now wonder, if I might get into troubles taking the bus from Chengdu to SP or from SP to Jiuzhaigou in February, because I read online that sometimes the busses don't run in winter due to weather issues. Is that likely to happen in February? I really dont want to book a flight from Jiuzhaigou, if theres the possibility that I wont even get there ...
thanks!