Spring (March to May) and autumn (September to November) are the best seasons for the high trail. April and May bring wildflowers on the trail and good visibility; October has reliably clear skies and comfortable temperatures. The winter months (December to February) are cold at altitude but often clear, and some hardy trekkers prefer the solitude of off-season visits.
The summer monsoon (June to September) is the most problematic period. Rainfall loosens the steep slopes above the trail and landslides have buried sections of path. The worst months are July and August. If you must go in summer, get current local information about trail conditions before starting — this is not something to improvise. The guesthouses at Qiaotou will know which sections are open and which are not.