When is the best time to visit Guilin and worse according to weather?

Generally speaking, March to April and August to September is two best periods to visit this scenic area. The climate is cool and comfortable during March and April. In addition, tourists can smell the fragance of sweet-scented osmanthus.

It's not suggested to visit there in winter. Tourists cannot see the abundant river water because winter belongs to rainless period.

Is the skies not clear in December/January i.e foggy and no sight?

Yes, at that time, there will be a lot of fog in the morning and at dusk, but it will be clear at the noon. Well, in winter, you can also go to visit the karst lansforms, such as silver cave, reed flute cave. Wear warm though!